# Need help with exposure question



## PJM (Oct 26, 2018)

I was out playing with my camera today checking out the effects of aperture on depth of field.  I ended up with two photos with different exposures and I'm trying to understand why.

The camera is a Nikon D5600 with a 18-55 mm, f/3.5-5.6 lens.
Both photos were taken in auto exposure mode and metering mode = pattern.
Both were also taken in aperture priority mode.
For the first  picture I set ISO = 100, f/4.5.   The camera set the shutter speed to 1/640.

For the second picture I set ISO = 800, f/22.  The camera set the shutter speed to 1/200.

Since the camera was in auto exposure mode I would expect the exposures to be more similar and am trying to understand why the second came out lighter.


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## Derrel (Oct 26, 2018)

I would guess that slight variation is about 4/10 of an EV value different....might just have come down to the JPEG engine's processing of the overall capture. But definitely, the first shot looks a bit nicer to me. How close in time are the frames? A few seconds apart?


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## Ysarex (Oct 26, 2018)

Another possibility is the minor framing variation (lighter version you titled the camera down a bit compared with the darker version). That's enough for the pattern metering to re-calc a minor difference.

Joe


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## AlanKlein (Oct 26, 2018)

That's why I bracket exposures on my landscape shots many times and shoot with a tripod.


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## photo1x1.com (Oct 27, 2018)

Doing the maths, this is the absolute same exposure

From ISO100 to ISO 800:+ 3EVFrom f4.5 to f22:- 4.67EVFrom 1/640sec to 1/200sec:+ 1.67EV∑0
[TBODY]
[/TBODY]
So IMO there´s actually two things that could have happened: 

The light got brighter (sun cam out)
There is a difference between f-stop (the nominal specs given by the manufacturer of the lens), and the so called t-stop (the real light transmission through your lens).
These will explain the difference in brightness, but not why your camera didn´t compensate. However, that does happen. In my experience cameras are not that consistent in their metering. 
I didn´t use any automatic or semiautomatic exposure modes for years because I wasn´t happy with the results (I am/was a Canon shooter). That first changed when they introduced the 5D MkIII.
I think the difference in your case isn´t all that bad.


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## Ysarex (Oct 27, 2018)

photo1x1.com said:


> Doing the maths, this is the absolute same exposure
> 
> From ISO100 to ISO 800:+ 3EVFrom f4.5 to f22:- 4.67EVFrom 1/640sec to 1/200sec:+ 1.67EV∑0
> [TBODY]
> ...



Those are not the absolute same exposures. Doing the math there is a 3 stop difference between the two exposures. And so as Derrel suggested the variation could also be in the camera electronics as it compensated for the exposure difference.

Joe


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## PJM (Oct 27, 2018)

Thanks for all the replies.  While I understand the fundamentals of exposure there are lots of nuances that I still have to learn and this all helps.

To answer the first question, they were taken probably 15 seconds apart, enough time for me to change the settings.

So for next time, take more pictures (bracketing) and use a tripod.

Thanks again.
Pete


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## photo1x1.com (Oct 27, 2018)

Ysarex said:


> photo1x1.com said:
> 
> 
> > Doing the maths, this is the absolute same exposure
> ...


Joe, you know I value your knowledge, but I wonder why your maths are different. So I recalculated and even took my camera to be on the safe side:

Let´s start with ISO 
100 0.00 
125 0.33
160 0.67
200 1.00 
250 1.33
320  1.67
400 2.00
500 2.33
640 2.67
800 3.00 
Next Aperture : 
5 2.67
5,6 2.33 
6,3  2.00
7,1 1.67
8,0 1.33 
9 1.00 
10  0.67 
11 0.33
13 0.00
14 -0.33 
16 -0.67
18 -1.00 
20  -1.33
22 -1.67
and finally Shutter Speed 
1/500  -1.33
1/400 -1.00
1/320 -0.67 
1/250 -0.33
1/200 0.00


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## Ysarex (Oct 27, 2018)

photo1x1.com said:


> Ysarex said:
> 
> 
> > photo1x1.com said:
> ...



My maths aren't different. ISO is not a determinent of exposure. In the above examples exposure is a function of shutter speed and f/stop. Look at the standard definition of exposure: In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. It matters; and in this case it could matter because the electronic processing the camera does to apply ISO brightening *after the exposure* could be one of the suspects. Don't let the triangle heads cloud your thinking.

Joe


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## photo1x1.com (Oct 27, 2018)

Ysarex said:


> photo1x1.com said:
> 
> 
> > Ysarex said:
> ...


Thanks for the clarification, of course you are techically correct . I remember we had a similar discussion a while ago. I wonder what would be a better term. I tend to use the word brightness, but in this case it would definitely be wrong.


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## PJM (Oct 27, 2018)

Correct me if I'm thinking wrong....
So I need to think of ISO differently from film.  Changing ISO on the digital camera does not really change anything about the sensor.  Whereas different ISO or ASA films were physically different, changing ISO on the digital camera is about how the camera interprets or processes the light captured by the sensor.

Pete


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## john.margetts (Oct 27, 2018)

PJM said:


> Correct me if I'm thinking wrong....
> So I need to think of ISO differently from film.  Changing ISO on the digital camera does not really change anything about the sensor.  Whereas different ISO or ASA films were physically different, changing ISO on the digital camera is about how the camera interprets or processes the light captured by the sensor.
> 
> Pete


That is correct.


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## john.margetts (Oct 27, 2018)

Ysarex said:


> My maths aren't different. ISO is not a determinent of exposure. In the above examples exposure is a function of shutter speed and f/stop. Look at the standard definition of exposure: In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. It matters; and in this case it could matter because the electronic processing the camera does to apply ISO brightening *after the exposure* could be one of the suspects. Don't let the triangle heads cloud your thinking.
> 
> Joe


You are quite correct, Joe, but you are on a hiding to nothing trying to get that accepted now that "everyone" knows about the exposure triangle. The curse of Youtube allowing everyone and his dog to post 'educational' videos.


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## Derrel (Oct 27, 2018)

I looked at the EXIF information. In the 800 ISO shot, the Gain Control setting, it lists *Low Gain Up*. In the 100 ISO shot, we have Gain Control: None.

So...at 800 ISO, the JPEG processing was done with added Gain control added into the processing mixture.

Interestingly, additionally I see that in the ISO 100 shot, which was made at f/4.5, you have a slight bit of selective focus effect occurring: the foreground bush and its lovely red berries are rendered in crisp focus, but the background of the woods is clearly,and obviously, slightly de-focused. In the 800 ISO shot, made at f/22, the background is more subtly out of focus...it's not really blurry, but it's in-between sharp and de-focused.

Back in the 1980's, when Nikon _invented_ multi-segment light metering and scene analysis, the Nikon FA was fitted with an "8-bit microprocessor", as Nikon boasted, and the FA camera had a memory bank of over 100,000 actual scenes that had been photographed, measure,metered,and analyzed. Things like 3-D, color-aware light metering and dynamic range optimization have advanced markedly since those days if the FA and multi-segment light metering and exposure control. Today *the camera not only meters the scene, but processes the final out of camera JPEG image*!. One thing I notice is that, in the photo that has the greater depth of field, the f/22 shot done at ISO 800, there is more brightness in the slightly shadowed areas on the fir trees in the background. In other words, because the background is slightly more-recognizable, and more in-focus, I suspect that the JPEG processing has been biased to add a slight bit of brightness to the background due to 1) ISO 800 use and 2)slightly more in-focus, and thus deserving of being "seen". 3) Gain [ brightening-up] being added to the processing

In the f/4.5 shot, which is likely with the lens wide-open at the used 35mm focal length setting on the 18-55 lens, the camera's processing is favoring the foreground exposure, and the background brightness is what one gets with NO gain control added, a pretty straight-up scene analysis and image processing effort. The 100 ISO in use would likely be indicative of a well-lighted scene.

When one starts looking into how Nikon meters with new cameras, they have a color-aware, and distance-aware, "3-D RGB Color Matrix Metering" that uses at the low end cameras, 1,005 sensor measurements, up to many thousands of measurements on higher-priced camera models. The entire scene, the distances, the focused distance, the ISO,. the geographic location, and the time clock...all of those things play a part in the metering and scene analysis. The clock you say? Combined with the city/time zone location the user inputs, it tells the camera night from day; at 12 midnight in Seattle, a large, bright orb in a darker field is either the moon, or a street lamp; at 12 Noon in Seattle a large, bright orb seen against a darker field is...the Sun in the sky.

Reading the colors? White sand? Gray sand? Brown sand? The color-sensing ability of the metering can determine the colors of things AND determine their degree of reflectivity. The camera can then expose, and process, and thus determine how the scene might best be rendered as an out of camera JPEG.

Your shots are different in time by enough that some slight cloud cover over the sun _could_ possibly have altered actual scene brightness, but my experience with Nikon matrix metering is that is is quite affected by larger bright areas; center-weighted Nikon metering is less-affected by bright areas; this is where the slight framing variations Ysarex mentioned could come into play; still, we do not have enough information to really draw conclusive, valid conclusions about why the two shots are different, but my vote goes to ISO levels, 100 vs 800, and no gain versus Low gain Up on the 800 ISO shot, thus brightening it up.

Sorry for the long post on this, but hey...


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## AlanKlein (Oct 27, 2018)

Ysarex said:


> My maths aren't different. ISO is not a determinent of exposure. In the above examples exposure is a function of shutter speed and f/stop. Look at the standard definition of exposure: In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. It matters; and in this case it could matter because the electronic processing the camera does to apply ISO brightening *after the exposure* could be one of the suspects. Don't let the triangle heads cloud your thinking.
> 
> Joe


A distinction without a difference.  ISO is one of the three variables that have to be set to adjust for proper exposure on the final image.


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## john.margetts (Oct 27, 2018)

As I said above, Joe is on a hiding to nothing with his accuracy. The three variables for getting the exposure right are light, aperture and time - all three are under the photographer's control (or should be). 

There are occasions when wrongly thinking ISO is a part of exposure prevents a photographer from producing a good picture. There are no occasions when a full understanding gets in the way.

Sent from my 8070 using Tapatalk


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## AlanKlein (Oct 27, 2018)

john.margetts said:


> As I said above, Joe is on a hiding to nothing with his accuracy. The three variables for getting the exposure right are light, aperture and time - all three are under the photographer's control (or should be).
> 
> There are occasions when wrongly thinking ISO is a part of exposure prevents a photographer from producing a good picture. There are no occasions when a full understanding gets in the way.
> 
> Sent from my 8070 using Tapatalk



You have no control of the light (natural).  You do have control of the film emulsion speed (ASA or ISO) in a film camera or gain of the digital amplifiers (ISO) in a digital camera. The two other variables are aperture and shutter speed (time).   All three are part of getting the proper exposure on the final result.


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## 480sparky (Oct 27, 2018)

The difference may also be strictly mechanical.   Maybe the shutter runs a bit long at 1/200 and is actually 1/175.  Or f/22 is actually closer to f/20.


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## john.margetts (Oct 27, 2018)

AlanKlein said:


> You have no control of the light (natural).  You do have control of the film emulsion speed (ASA or ISO) in a film camera or gain of the digital amplifiers (ISO) in a digital camera. The two other variables are aperture and shutter speed (time).   All three are part of getting the proper exposure on the final result.


I have plenty of control over the light. If I am outdoors, I can choose the weather and the time of day. I have a flash gun. Indoors, I have even more control.

The incorrect idea of the 'exposure triangle' give a false idea that altering the three gives equivalent exposures and equivalent results. An example: set the camera at ISO 400 (could be any other ISO number). Determine that the optimum exposure is 1/100 at f/16. Leaving the ISO the same, you could change the exposure to 1/200 at f/11 or 1/400 at f/8. The results will be the same. Change the ISO to 25,000 and 1/100 at f/3.5 and the results will not be the same - the new exposure is not equivalent. With most sensors on the market, you are now in the realms of noise because you are significantly under-exposing and compensating with electronic gain.

Sent from my 8070 using Tapatalk


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## AlanKlein (Oct 27, 2018)

john.margetts said:


> AlanKlein said:
> 
> 
> > You have no control of the light (natural).  You do have control of the film emulsion speed (ASA or ISO) in a film camera or gain of the digital amplifiers (ISO) in a digital camera. The two other variables are aperture and shutter speed (time).   All three are part of getting the proper exposure on the final result.
> ...


I agree you have some control of the light, more so inside with artifical lights.  That's actualy a fourth variable not usually part of the setting especially when shooting outdoors and using ambient light.  But ISO or film speed is a legitimate setting that you can change to affect the final picture.  The point is if you leave the aperture or shutter the same, you have to adjust either the iso or shutter speed or both.  All three effect each other.  

Noise due to high ISO  is just a problem just like changing speed of the film effects grain, aperture effects depth of field, or shutter speed effects blurriness.  But these things are separate from getting the right exposure which require the three parts of shutter, aperture and ISO to interplay.  The "exposure triangle" is a clear way of understanding how to set your camera.  It's not a false idea.


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## WayneF (Oct 27, 2018)

john.margetts said:


> I have plenty of control over the light. If I am outdoors, I can choose the weather and the time of day. I have a flash gun. Indoors, I have even more control.



You two guys are funny (to be PC, I never said laughable    ). How would you suggest taking a satisfactorily exposed picture without addressing the proper ISO to do it?  (not speaking of relying on automation to do it for you).



> The incorrect idea of the 'exposure triangle' give a false idea that altering the three gives equivalent exposures and equivalent results. An example: set the camera at ISO 400 (could be any other ISO number). Determine that the optimum exposure is 1/100 at f/16. Leaving the ISO the same, you could change the exposure to 1/200 at f/11 or 1/400 at f/8. The results will be the same. Change the ISO to 25,000 and 1/100 at f/3.5 and the results will not be the same - the new exposure is not equivalent. With most sensors on the market, you are now in the realms of noise because you are significantly under-exposing and compensating with electronic gain.



The actual "triangle" concept makes no real sense to me, but it is established in literature, and does no harm, might even help beginners.  The Three factors are very important though, and of course exposure is obviously the result of the three factors of aperture, shutter speed, and ISO.  There is the implied concept of the ISO being chosen correctly to match the exposure of the light (the result of aperture and shutter speed) to the sensor sensitivity.

Yes, of course, a higher ISO can affect the picture, but not the matched exposure.

And of course the exact same is also true of aperture and shutter speed, affecting depth of field and motion blur (yes, can ALSO be very different pictures, but can still be a matched proper exposure). The trick is to select those of the three that are important for satisfactory result, and of course the proper match of the three for exposure.

From time immemorial (or at least the 150+ years since, say Matthew Brady), exposure has been about aperture, exposure duration, and sensor sensitivity to light.  Digital may use a different technique (like we always wished boosting film speed did), but ISO still affects the histogram exposure in the same way it always did.


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## 480sparky (Oct 27, 2018)

Just to show the difference between the two 'equal' exposures:
A histogram of the 1/640  f/4.5  ISO 100 image:








And a histo of the 1/200 f/22 ISO 800 image:








The blue channel of the ISO 100 image has a lot of unexposed pixels and _some_ blown-out red pixels, while the lighter ISO 800 image has fewer unexposed blue pixels and lots of blown-out red pixels.

While very similar in shape, you can see that although the ISO 100 has a median pixel brightness of 85 (compared to the 'lighter' f/22 image of 108).  This explains why the ISO 800 images looks lighter. 

But what's even more interesting is the ISO 800 image histrogram is noticably flat compared to the 100 image.  Especially in the pixel counts in the 35-150 brightness range.  This means the ISO 100 image contains _more data_. And more data may well affect how the demosaicing algorithm renders the final JPEG.


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## john.margetts (Oct 27, 2018)

WayneF said:


> You two guys are funny (to be PC, I never said laughable    ). How would you suggest taking a satisfactorily exposed picture without addressing the proper ISO to do it?  (not speaking of relying on automation to do it for you).


Because I am not confusing exposure with brightness of final image. Your ISO setting affects the brightness of the final image, not the exposure. You can achieve the same thing after the shot is taken and the image file is downloaded to your computer. Lightroom has an "exposure" slider which will brighten or darken the image but clearly has no effect on what the camera has already done and so has nothing to do with the exposure.


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## john.margetts (Oct 27, 2018)

john.margetts said:


> Ysarex said:
> 
> 
> > My maths aren't different. ISO is not a determinent of exposure. In the above examples exposure is a function of shutter speed and f/stop. Look at the standard definition of exposure: In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. It matters; and in this case it could matter because the electronic processing the camera does to apply ISO brightening *after the exposure* could be one of the suspects. Don't let the triangle heads cloud your thinking.
> ...


I should have listened to myself!


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## Derrel (Oct 27, 2018)

480sparky said:


> The difference may also be strictly mechanical.   Maybe the shutter runs a bit long at 1/200 and is actually 1/175.  Or f/22 is actually closer to f/20.



I doubt that the shutter timing is off, since that's electronically timed, but the lens aperture not being quite right--that's a resounding *YES, perhaps*. At small apertures, like f/13 to f/45 let's say, even a very tiny amount of incorrect diameter can be a very large percentage of error. At times, some diaphragms do not stop down to a regular,exactly-uniform shape, with one or two of the blades not quite forming the correct shape...it is possible that the slight over-exposure could be attributed to the diaphragm not stopping down to f/22, but to a slightly larger sized hole. On most Nikkor lenses, except for the new E-diaphragm models, the diaphragm actuation is all-mechanical. And as we know, mechanical systems are prone to slight inconsistencies.


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## WayneF (Oct 27, 2018)

john.margetts said:


> WayneF said:
> 
> 
> > You two guys are funny (to be PC, I never said laughable    ). How would you suggest taking a satisfactorily exposed picture without addressing the proper ISO to do it?  (not speaking of relying on automation to do it for you).
> ...



So I guess  you are saying you imagine your notion is  somehow correct for digital, but that you are obviously wrong for film? 

My own notion is about the histogram that I can see, and the usability of that image that I can see and access.  Both film and digital satisfy the normal and accepted concept of exposure...  for both, we just balance the three factors to produce the usable image.

But you failed to answer my question that you quoted. How do you take a properly exposed picture (the usable picture) without consideration of proper ISO? That must be very tedious, and interesting to watch..


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## WayneF (Oct 27, 2018)

PJM said:


> Correct me if I'm thinking wrong....
> So I need to think of ISO differently from film.  Changing ISO on the digital camera does not really change anything about the sensor.  Whereas different ISO or ASA films were physically different, changing ISO on the digital camera is about how the camera interprets or processes the light captured by the sensor.
> 
> Pete




Digital ISO is an amplification, but it changes anything that we can get out of the sensor or the raw file or the JPG file.
The only way to access the non-amplified data is to set ISO low to native value.  I suppose that could be a misguided goal, but you still have to set ISO to achieve it.
That might be a technical issue, but to US users, it is just semantics.
I don't see any reason to confuse the newbies with it. They have a lot more to deal with early on. Like learning to get aperture, shutter speed and ISO matched right.


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## Ysarex (Oct 27, 2018)

john.margetts said:


> Ysarex said:
> 
> 
> > My maths aren't different. ISO is not a determinent of exposure. In the above examples exposure is a function of shutter speed and f/stop. Look at the standard definition of exposure: In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. It matters; and in this case it could matter because the electronic processing the camera does to apply ISO brightening *after the exposure* could be one of the suspects. Don't let the triangle heads cloud your thinking.
> ...



I've been at work all day teaching a proper understanding of exposure to my students -- seems I missed all the fun.

Yes I know, ignorance abounds and Youtube is it's name. I describe Youtube to my students as a sewer. You're in the sewer on your hands and knees up to your elbows and of course can't see through the crap. In the next hundred yards the bottom of the sewer is covered with millions of pebbles. Strewn amongst those pebbles are a handful of priceless precious stones. Oh please don't tell me you watched that exposure triangle crap! It's going to be a long 100 yards! 

Joe


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## Ysarex (Oct 27, 2018)

WayneF said:


> john.margetts said:
> 
> 
> > I have plenty of control over the light. If I am outdoors, I can choose the weather and the time of day. I have a flash gun. Indoors, I have even more control.
> ...



It confuses beginners by confusing cause and effect. That's never a good idea.



WayneF said:


> The Three factors are very important though, and of course exposure is obviously the result of the three factors of aperture, shutter speed, and ISO.  There is the implied concept of the ISO being chosen correctly to match the exposure of the light (the result of aperture and shutter speed) to the sensor sensitivity.
> 
> Yes, of course, a higher ISO can affect the picture, but not the matched exposure.
> 
> ...



No. During that past period of time -- since long before you came along -- exposure was well understood and clearly defined. From Ilfords The Manual of Photography first published in *1890*: "_When a photograph is taken, light from the various areas of the subject falls on corresponding areas of the film for a set time. The effect produced on the emulsion is, within limits, proportional to the product of the illuminance E and the exposure time t. We express this by the equation
H = Et
Before international standardization of symbols, the equation was E = It (E was exposure, I was illuminance) and this usage is sometimes still found. The SI unit for illuminance is the lux (lx). Hence the exposure is measured in lux seconds (lx s)._"

Here's the definition from Wikipedia that I posted earlier that agrees with the definition above and that is correct: "_In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance._"

Underline ISO in that definition and repost it.

Joe



WayneF said:


> Digital may use a different technique (like we always wished boosting film speed did), but ISO still affects the histogram exposure in the same way it always did.


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## AlanKlein (Oct 27, 2018)

Joe,  We understand that exposure is how many photons falls on the film or digital sensor.  The the aperture and shutter speed control the photon quantity.  But that's only of interest to engineers and camera designers.  For average photographers, who are learning how to set proper exposure on their cameras, they have to input ISO as one of the variables to get the final picture to look exposed correctly.  If ISO (ASA) wasn;t important, then you would (not) have that control on a light meter.  IF you set ISO wrong, you'll get an over or under exposed picture.

Beyond that we've entered the world of word games.  So I'm out of here.


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## Ysarex (Oct 27, 2018)

WayneF said:


> john.margetts said:
> 
> 
> > WayneF said:
> ...



Proper ISO? Anyway, you don't. ISO is an important consideration when making an exposure. That does not however make ISO an exposure determinant. "Exposure" has a definition that makes cause and effect clear. This old analogy is useful.

You're going to turn on the water and fill a beaker (ISO). You have constant water pressure at the time (scene luminance). The faucet handle is a little special and is equipped with click stops so that you can open it one, two, three, four, etc. clicks and each click opens the value more (aperture). You take an 8 ounce beaker and hold it under the faucet and open it two clicks for 5 seconds (time - shutter speed). The beaker nearly fills. Congratulations! Set that aside. Now reach up on the shelf and grab a 16 ounce beaker. Hold the 16 ounce beaker under the faucet and open it two clicks for 5 seconds. Which beaker has more water in it? The size of the beaker doesn't determine the volume of water.

Joe



WayneF said:


> That must be very tedious, and interesting to watch..


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## Ysarex (Oct 27, 2018)

AlanKlein said:


> Joe,  We understand that exposure is how many photons falls on the film or digital sensor.  The the aperture and shutter speed control the photo quantity.  But that's only of interest to engineers and camera designers.  For average photographers, who are learning how to set proper exposure on their cameras, they have to input ISO as one of the variables to get the final picture to look exposed correctly.  If ISO (ASA) wasn;t important, then you would have that control on a light meter.  IF you set ISO wrong, you'll get an over or under exposed picture.
> 
> Beyond that we've entered the world of word games.  So I'm out of here.



ISO is important -- never said it wasn't. Above I just confirmed it's needed to get a proper exposure. The problem shows up when you change ISO's roll and try to turn it into an exposure determinant. Read the water faucet analogy in my last post.

The exposure triangle is presented with three variables and they are all presented as determinants of exposure. They are then further presented as each controlling independent additional variables. Aperture = DOF, Shutter speed = motion/blur, and ISO = noise. Beginners read that and believe it. That's wrong and the beginners at that point become confused about cause and effect. ISO does not cause noise. If anything what ISO does suppresses noise. Ultimately their confusion leads them to making mistakes and taking worse photos than they otherwise could. Today with the arrival of ISO-invariant sensor a new twist gets added in and the triangle becomes more confusing.

Joe


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## AlanKlein (Oct 27, 2018)

Ysarex said:


> AlanKlein said:
> 
> 
> > Joe,  We understand that exposure is how many photons falls on the film or digital sensor.  The the aperture and shutter speed control the photo quantity.  But that's only of interest to engineers and camera designers.  For average photographers, who are learning how to set proper exposure on their cameras, they have to input ISO as one of the variables to get the final picture to look exposed correctly.  If ISO (ASA) wasn;t important, then you would have that control on a light meter.  IF you set ISO wrong, you'll get an over or under exposed picture.
> ...



What confusion and how does it lead to mistakes?


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## Ysarex (Oct 27, 2018)

WayneF said:


> PJM said:
> 
> 
> > Correct me if I'm thinking wrong....
> ...



Wince! "amplification" and or "gain" have been used a lot especially in the past to describe what's going on. Those terms carry connotations with them from the audio industry that aren't quite right for digital photo. Problem is multiple methods are employed to "brighten" the image. The signal from the sensor is analog and in some cameras absolutely that signal is passed through amplification. However in more and more cameras now the signal goes straight to the ADC and the brightening of the image is done by digitally scaling the data. In more and more cameras now a hybrid combination of those methods are used.



WayneF said:


> but it changes anything that we can get out of the sensor or the raw file or the JPG file.
> The only way to access the non-amplified data is to set ISO low to native value.  I suppose that could be a misguided goal, but you still have to set ISO to achieve it.
> That might be a technical issue, but to US users, it is just semantics.



Unless it's not a misguided goal but an appropriate way to get the desired image. In which case it can really help to understand what exposure is and what ISO is.



WayneF said:


> I don't see any reason to confuse the newbies with it. They have a lot more to deal with early on. Like learning to get aperture, shutter speed and ISO matched right.



No argument early on, but if you start them off confused and all twisted in a knot then later on it can be much harder to straighten them out when it might matter.

Joe


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## Ysarex (Oct 27, 2018)

AlanKlein said:


> Ysarex said:
> 
> 
> > AlanKlein said:
> ...



I get it all the time from my students who have been "traingled." *Confusion:* ISO causes noise. Therefore if I raise the ISO that will make my photo noisier. *Mistake:* Stuck in a low light situation and need to take a hand-held photo. To get the shutter speed I'd like I'll have to raise the ISO to 6400. Yikes! I can't do that, that's too much noise! Ok, ok, I'll just set the ISO to 3200 and get within 2/3 to 1/2 a stop of a zeroed meter. I can probably get away with 1/60 sec. instead of 1/100. Click. They get a blurry noisier photo.

I waste a lot of time repairing that damage. ISO does not cause noise. If anything in many cameras it helps suppress noise. The triangle confuses cause and effect.

We're experiencing a slow but sure hardware change these past few years and certainly in the years to come. Many of us now are shooting ISO invariant sensors in our cameras and many more of us will be. To take maximum advantage of that it's going to help to have a good understanding of what's going on. The first fix to the exposure triangle if you're not going to dump it as a bad idea is to at least replace the ISO = noise side of the triangle with ISO = DR -- that could be useful.

Joe


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## WayneF (Oct 27, 2018)

Ysarex said:


> ISO does not cause noise. If anything in many cameras it helps suppress noise.



That is truly laughable.  The gain required by digital ISO of course necessarily amplifies the noise as much as the signal.  Visibility soon becomes an issue.
The camera amplification does have better ways to do it than in Lightroom (and Lightroom range is limited to only about 5 EV).  
But the only way ISO lowers noise is an ISO lower than native, like ISO 50, which reduction does decrease  both noise and signal (and dynamic range).

No one has answered my question about how you achieve proper exposure without considering ISO to do it.    

If you do of course use ISO (as I strongly suspect), then this is just unnecessary semantics at any entry level suitable for the triangle.  Trying to show off that you know something to beginners is in poor taste.
If you don't use ISO (and depend on Lightroom?), then that's just dumb, and you certainly did NOT achieve any proper exposure.
Either way, there is no point or any desire to continue this dumb stuff with you.   Have fun.

I also wanted to tell someone else here today in another thread the classic "When all around you are wrong, maybe you should reconsider your own opinion".  But I find no private messaging here, and I respect him too much to call attention to it online.  And I do that sometimes too.


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## Ysarex (Oct 27, 2018)

WayneF said:


> Ysarex said:
> 
> 
> > ISO does not cause noise. If anything in many cameras it helps suppress noise.
> ...



So you agree then that ISO doesn't cause the noise -- amplifying the noise is not the same as causing it. Cause and effect is important. You seem very confused.



WayneF said:


> Visibility soon becomes an issue.
> The camera amplification does have better ways to do it than in Lightroom (and Lightroom range is limited to only about 5 EV).
> But the only way ISO lowers noise is an ISO lower than native, like ISO 50, which reduction does decrease  both noise and signal (and dynamic range).



There are different sources of noise. Most of the noise that average photographers see in their photos is shot noise (not caused by ISO). ISO brightening makes that noise visible but does not cause it. Read noise comes from the camera electronics as the signal is processed and ISO analog amplification definitely suppresses read noise.



WayneF said:


> No one has answered my question about how you achieve proper exposure without considering ISO to do it.



I did.

And I see that you have failed to repost that definition of exposure with ISO underlined.

Joe



WayneF said:


> If you do of course use ISO (as I strongly suspect), then this is just unnecessary semantics at any entry level suitable for the triangle.  Trying to show off that you know something to beginners is in poor taste.
> If you don't use ISO (and depend on Lightroom?), then that's just dumb, and you certainly did NOT achieve any proper exposure.
> Either way, there is no point or any desire to continue this dumb stuff with you.   Have fun.
> 
> I also wanted to tell someone else here today in another thread the classic "When all around you are wrong, maybe you should reconsider your own opinion".  But I find no private messaging here, and I respect him too much to call attention to it online.  And I do that sometimes too.


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## photo1x1.com (Oct 28, 2018)

I do have to defend Joes position. For us nerds who are able to take part in this advanced discussion, many things are somewhat logical. Of course, if the sun goes down it gets dark, and we have to compensate for that.
But *some* beginners don´t get that. From reading many facebook groups, here in the forum and also from people asking me when I´m out and about shooting, I know that *some* beginners usually don´t take the light situation into the equation. They only think in their exposure triangle, and that gets them confused. I for one have never used the phrase exposure triangle at all - having a triangle doesn´t really make it easier to understand, so it doesn´t add anything.

I for one will try to change my language from now on.
One thing that hasn´t been answered yet though is:
How would you call that brightness of the image, made up of "incomming" light,  aperture diameter, shutter speed and ISO, that is commonly referred to as exposure?


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## john.margetts (Oct 28, 2018)

photo1x1.com said:


> I for one will try to change my language from now on.
> One thing that hasn´t been answered yet though is:
> How would you call that brightness of the image, made up of "incomming" light,  aperture diameter, shutter speed and ISO, that is commonly referred to as exposure?


I call it brightness.



Sent from my 8070 using Tapatalk


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## john.margetts (Oct 28, 2018)

AlanKlein said:


> What confusion and how does it lead to mistakes?


The confusion in the opening post where the poster could not understand why two photos with the 'same' exposure looked different. A later poster posted the histograms of the two photos concerned. The difference between the two exposures are clear. The larger exposure (taken at a lower ISO) has a different shape histogram to the smaller exposure taken at a higher ISO. The larger exposure contains more information which is more than just academic.


Sent from my 8070 using Tapatalk


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## Ysarex (Oct 28, 2018)

photo1x1.com said:


> I do have to defend Joes position. For us nerds who are able to take part in this advanced discussion, many things are somewhat logical. Of course, if the sun goes down it gets dark, and we have to compensate for that.
> But *some* beginners don´t get that. From reading many facebook groups, here in the forum and also from people asking me when I´m out and about shooting, I know that *some* beginners usually don´t take the light situation into the equation. They only think in their exposure triangle, and that gets them confused. I for one have never used the phrase exposure triangle at all - having a triangle doesn´t really make it easier to understand, so it doesn´t add anything.
> 
> I for one will try to change my language from now on.
> ...



Yep, you've zeroed in on the source of the problem here. When Alan first posted he used the term "proper exposure." He was never thinking of "exposure." In Wayne's first post (2nd sentence after throwing an insult) he uses the term "satisfactorily exposed." I quoted a definition earlier from Ilford's The Manual of Photography which is one of the most respected references in our discipline. They address this issue in the text and they solve it by carefully using two different terms. They explain why. "Exposure" they insist has a clear meaning and it's critical that it's definition not be confused with what they decide to call "camera exposure." "Camera exposure" includes ISO. They settle on "camera exposure" because the other options are too loaded with subjective land mines. Defining "exposure" is simple and it's settled. We settled it a long time ago. "Correct exposure" or "proper exposure" or "satisfactory exposure" is something else and if we set about trying to define that in this venue we're in for a much bumpier ride than we've gotten so far.

There are good reasons to keep these two concepts separate; Ilford found it necessary. But they both have the word "exposure" in them and it's really hard to get folks to understand the distinction and the need for it. When you tell everyone that ISO is not an "exposure" determinant they hear you saying ISO is not a "correct exposure" determinant and that they think is just crazy.

Unfortunately we're stuck here. "Proper exposure" was used by both Alan and Wayne. That's what most photographers mean when they say "exposure." It's a colloquial usage. What exactly is "proper exposure"? The next step sends you straight down the rabbit hole. Is it the translation of a specific gray value in the scene to a specific gray value in an RGB image? How is a light meter adjusted? In any attempt to try and define "proper exposure" it won't be long before someone comes along with, "it's whatever you want it to be, it's completely subjective!"

Ilford's solution feels unsatisfactory. By using "camera exposure" they decided to just go around the mine field -- not goin' there, ha! When it comes time to understand how our cameras actually work (throughout this thread I kept repeating "cause and effect") we need the established meaning of the term "exposure." We can't let that term and it's definition be changed. So we still have your question what term do we use when we mean; "that brightness of the image, made up of "incomming" light,  aperture diameter, shutter speed and ISO, that is commonly referred to as exposure?" I think it's too established colloquially and we're stuck with it and we're stuck with the conflicting meanings. Just always use the adjective of your choice (correct, proper, satisfactory, etc.) in front of exposure when you don't mean exposure.

As for the definition of "correct exposure" -- I'm not goin' there, ha!

Joe

EDIT: The exposure triangle mess is unfortunate. Beginners need to learn to use and adjust their cameras. The ET as a model can be helpful at first. Many enthusiast photographers will never need to move beyond that and enough said.

The folks who spread the ET model around found it satisfying to create this balanced structure so that each side/vertice of the triangle has equal weight to the other sides. Each side adjusts exposure, oops "correct exposure" while at the same time also adjusting an independent variable. The independent variable they chose for ISO is noise.

For most of us the noise we see in our photos is shot noise. Shot noise is a function of exposure. The less you expose a digital sensor the more shot noise you're going to see. ISO correlates with this in that if we use the camera meter and raise the ISO then the meter recalculates a reduced exposure which gives us more shot noise. Correlation and cause are two very different things.

There is however a factor that ISO is causally responsible for. Increasing ISO reduces DR. Here's a graph of DR over ISO for a Nikon D7200: Photographic Dynamic Range versus ISO Setting. When ISO brightens the sensor output before or during ADC it's shaving DR straight off the top. Clipped highlights in a high ISO value image get clipped by the ISO brightening and may not be clipped in the exposure. The ET would make more sense if the independent variable associated with ISO were DR. At least in that case a causal relationship would exist. Then if they could just stop calling it the exposure triangle.....


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## Designer (Oct 28, 2018)

WayneF said:


> No one has answered my question about how you achieve proper exposure without considering ISO to do it.


See post #29, above.


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## Designer (Oct 28, 2018)

photo1x1.com said:


> - having a triangle doesn´t really make it easier to understand, so it doesn´t add anything.


Unfortunately, we do seem to be stuck with the "triangle" idea, at least for now, but even when in use by well-meaning individuals such a concept actually makes a "good/proper/correct" exposure MORE difficult, not easier.  Why wouldn't having only TWO variables (given the same existing light is the same) instead of three make anything easier?  When one wishes to increase the light, he can use flash or wait for a sunny day, which of course introduces the third variable (if one needs three variables).

So where does the "confusion" come from?  It comes from a fundamental misunderstanding of digital photography, and as long as beginners continue to rely on a "triangle" idea, they will continue to make mistakes.  Just as the OP has illustrated; by plugging in known variables but getting different results yields confusion.  

Now to the question of "what makes a "proper" exposure?  In digital, I would say that getting the most information you can get without overloading your sensor would be the correct answer.  Overloading an electronic sensor yields what we call "blown out", and is caused by such an overexposure that your camera's firmware cannot process the data to produce a viewable image.  Considering the complete concept, this is how the socks photograph was made: Capture as much information as you can (in the low light condition), and boost the gain AFTER the data has been captured.  Whether one has set the camera's ISO setting to a high value, or he does that on the computer later is irrelevant, the end result is the same.  

One more thing: since there is no such thing as "photons", @alan Kline, the concept of the filling of a container with "light particles" is a bad analogy, and leads to more confusion, therefore should not be used.  Inform the beginners how this stuff really works and you get less confusion, not more.


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## WayneF (Oct 28, 2018)

Designer said:


> WayneF said:
> 
> 
> > No one has answered my question about how you achieve proper exposure without considering ISO to do it.
> ...



No, in no way. That just keeps on talking around it, intently trying to evade the specific question. He should be a politician  (meaning, a politician of the worst kind).     Along with his adding some really stupid stuff like:  "ISO does not cause noise. If anything what ISO does suppresses noise. "  Really laughable.

The question meaning was this:  Suppose you want to take a picture of the crowd on Main Street, and you raise your camera to adjust for proper settings and do it. The Suns illumination does affect the brightness of the image you will see (as certainly also does the aperture, shutter speed and ISO selected), so there are the three settings necessary in an appropriate matched group for this proper exposure: aperture, shutter speed, and ISO.  First Basics of photography.  Each of the three requires selecting suitable choices for the situation (due to depth of field, motion blur, and sensor noise), or we could allow automation to chose something to do it (but other than exposure, it has no knowledge of the scenes actual requirements), but all three settings must absolutely be addressed.  ISO is one of the settings we are required to make for a proper exposure (proper meaning so that we do get a usable image file with an acceptable histogram... there is no other way to get a proper image file out of the camera other than to select the three suitable settings).  ISO is one of those extremely necessary settings to deal with, arguably one of the most important.

It is argued that digital ISO is just a gain amplification factor after actual instant of "exposure", which is just show-off clever in this context, but it is not useful in practice, or to newbies, since there is no other way to get the proper image file out of the camera without setting a suitable ISO too.  Any image file and any histogram WILL have this ISO result in it. It is what the camera does. It is what ISO does.  Setting ISO is one of the required ways we deal with situations, in order to get a proper and usable file out of the camera.  The three basic essentials required for newbies (or automation) to get a proper image is aperture, shutter  speed, and ISO. This was  of course true of film too.

My question, still totally ignored,  is: When standing on Main Street, how does one take any proper and usable image without concern for setting a usable ISO?  It is not a question about semantics of terms, it is about when standing on Main Street, what does one do without setting ISO?  Agreed, it is a stupid question (we all know the answer, we set ISO), but this has become a stupid thread.


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## Designer (Oct 28, 2018)

WayneF said:


> ..the image you will see ..


What you are looking at is the JPEG image that your camera's firmware has generated so you can view the data as a viewable image.  

This is not like the analog process of emulsion-based film photography.


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## john.margetts (Oct 28, 2018)

To get a 'proper and usable image' we set many things including ISO, focus mode, meter mode, actual focus but these are not a part of the exposure apart from the fact that you cannot get an image without setting them.

It is the 'exposure triangle' that caused the op's original concerns.


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## Ysarex (Oct 28, 2018)

WayneF said:


> Designer said:
> 
> 
> > WayneF said:
> ...



I answered your question directly. If you're not going to take the time to read through a thread you shouldn't keep returning to the thread and re-posting the same errors that have already been addressed. Such arrogance set in ignorance makes you look very much the fool. And I'm still waiting for you to repost that definition of exposure with ISO underlined.

Joe

Oh and, what happened to this: "Either way, there is no point or any desire to continue this dumb stuff with you. Have fun."


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## greybeard (Oct 28, 2018)

I think a lot of people think that by upping the ISO they are increasing the sensitivity of the sensor by juicing it up.  In fact, cranking up the ISO is more like turning up the output gain.  The weaker the signal, the noisier it becomes.  Image sensors are analog devices that have a noise floor.  The best way to avoid noise is proper exposure at the base ISO and, exposure is determined by lens aperture and shutter speed as determined by the camera's light metering system or a handheld meter.  Which means always shooting in good light, or shooting with a tripod, or shooting with flash or studio lights.  If you are shooting moving subjects or shooting with a tripod is impractical,  you will need to up the ISO to a point that will let you use the action stopping shutter speeds and smaller aperture for greater DoF.   I look at exposure vs ISO as a compromise to get the action stopping and DoF I need with an acceptable amount of noise that can be hidden in post processing.  dSLR's have gotten so good these days that I shoot in manual with auto ISO.


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## Tim Tucker 2 (Oct 29, 2018)

I think the main problem is the same as it always is, that too many use their knowledge of how a camera works to understand light rather than how light works to understand the camera. If you like, on the simplified diagram below, they read from the right rather than reading from the left:






With digital you can add that the less light you use, (the lower the exposure), to create an image with the desired brightness then the more noise you will see. The calibrated brightness levels programmed into your camera (ISO) take this into account and so are also programmed to remove a little of that noise. User defined brightness, deliberate underexposure in relation to the calibrated brightness levels programmed into your camera (ISO), does not and so no noise reduction takes place.

Simple...


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## n614cd (Oct 29, 2018)

Wow, such debate of terminology 
Just to clarify, I believe the following is correct:

Due to post processing or the exposure triangle; 99% of the photographers state exposure includes three aspects, shutter speed, aperture and ISO.

Technically, as a few have pointed out. Exposure is just a measure of the amount of photons which hit the sensor or film.
ISO settings in the age of film affected the sensitivity of the film to light. In digital, it affects how the raw sensor data is utilized. Note: How this is done is camera manufacturer specific, and often tied to the sensor itself.  

In digital, noise is defined as invalid or unwanted data. As you increase ISO, you are actually making the sensor more sensitive, however this comes at a cost. The cost is you actually increase noise, thereby reducing the signal to noise ratio.

For digital ISO, there are three general methods, a straight voltage gain applied to the sensor data before analog is converted to digital, or the gain is applied to the digital values after conversion, or a hybrid which combines the first two methods. Based on reading on the net, most newer cameras are hybrids, and involve anti-aliasing and other features after the digital conversion in an attempt to reduce noise.
When you shot in RAW, ISO is baked into the data. You cannot adjust it afterwards with darktable, Lightroom, Photoshop, GIMP... 

When you shot in JPEG, ISO is baked into the data. You cannot adjust it afterwards with darktable, Lightroom, Photoshop, GIMP...
darktable, Lightroom, and other products can adjust EV. EV is this concept is often a short hand for Exposure Value. This is done by formulas which amplify or decrease values in specific color channels across individual pixels. Each software has its own solution, and can often approximate each other; however they are not exact matches.
I have never seen the ability to take a picture with an ISO of 100, then keep the same shutter and aperture; and take a second shot with an ISO of 800, and be able to get them to match identically in view and histogram afterwards with post processing software.
The first point, and the last point is by far the most critical in terms of semantics. You can wail against the tide all you want, but at the end of the day, exposure outside of a technical discussion has come to mean the combination of ISO, Shutter Speed, and Aperture.  

The inability to effectively adjust the ISO afterwards with software in post processing, means that you must include ISO as you take the picture. A long time ago, people may have differentiated between "exposure" and "camera exposure"/"proper exposure"; however with almost no photographer using or needing to technically define "exposure" as just the light photons hitting the sensor, the first adjective (camera or proper) has been dropped from common usage. Leaving us where we are today, exposure means the triangle. 

Tim


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## Ysarex (Oct 29, 2018)

n614cd said:


> Wow, such debate of terminology
> Just to clarify, I believe the following is correct:
> 
> Due to post processing or the exposure triangle; 99% of the photographers state exposure includes three aspects, shutter speed, aperture and ISO.
> ...


No. You can't do anything to alter the sensitivity of the sensor. It is fixed in manufacture and ISO changes do not either raise or lower it. The noise most photographers see is not a function of anything ISO does to the sensor.




n614cd said:


> For digital ISO, there are three general methods, a straight voltage gain applied to the sensor data before analog is converted to digital, or the gain is applied to the digital values after conversion, or a hybrid which combines the first two methods. Based on reading on the net, most newer cameras are hybrids, and involve anti-aliasing and other features after the digital conversion in an attempt to reduce noise.
> [*]When you shot in RAW, ISO is baked into the data. You cannot adjust it afterwards with darktable, Lightroom, Photoshop, GIMP...
> 
> [*]When you shot in JPEG, ISO is baked into the data. You cannot adjust it afterwards with darktable, Lightroom, Photoshop, GIMP...
> ...



I have to run right now for a 1:00 pm appointment. That's trivially easy to do and I'll be happy to show you an example this afternoon when I return.



n614cd said:


> The first point, and the last point is by far the most critical in terms of semantics. You can wail against the tide all you want, but at the end of the day, exposure outside of a technical discussion has come to mean the combination of ISO, Shutter Speed, and Aperture.



 Given that I can thoroughly refute your last point (hang in there) you may want to reconsider this conclusion.

Joe



n614cd said:


> The inability to effectively adjust the ISO afterwards with software in post processing, means that you must include ISO as you take the picture. A long time ago, people may have differentiated between "exposure" and "camera exposure"/"proper exposure"; however with almost no photographer using or needing to technically define "exposure" as just the light photons hitting the sensor, the first adjective (camera or proper) has been dropped from common usage. Leaving us where we are today, exposure means the triangle.
> 
> Tim


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## Tim Tucker 2 (Oct 29, 2018)

n614cd said:


> ISO settings in the age of film affected the sensitivity of the film to light.



Camera settings don't affect the sensitivity of film one single jot... What the ASA/ISO setting did was adjust the exposure meter to a calibrated sensitivity (the sensitivity which is the ASA rating on the film) so it would indicate the *suggested* combination of aperture and shutter speed that would create the best exposure for film of that sensitivity.




n614cd said:


> The first point, and the last point is by far the most critical in terms of semantics. You can wail against the tide all you want, but at the end of the day, exposure outside of a technical discussion has come to mean the combination of ISO, Shutter Speed, and Aperture.



Exposure simply means the amount of light you allow to hit the sensor, or the range of point intensities recorded by the sensor.



n614cd said:


> In digital, noise is defined as invalid or unwanted data. As you increase ISO, you are actually making the sensor more sensitive, however this comes at a cost. The cost is you actually increase noise, thereby reducing the signal to noise ratio.



The sensitivity of the sensor remains unchanged, ISO only adjusts the output brightness and does a noise reduction. It is supposed to be transparent as in it does the calculation and post processing for you, but the downside to *decreased exposure* is a lower signal to noise. it's not a product of higher ISO, (higher ISO settings decrease noise because they are also programmed to remove some of it). All you do by setting a higher ISO is to recalibrate the meter so if reflects the *suggested* exposure for the brightness setting you've chosen to process the data at.


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## n614cd (Oct 29, 2018)

@Ysarex

Make sure to include the histogram for each before and after 

Sent from my SM-J737T using Tapatalk


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## Designer (Oct 29, 2018)

n614cd said:


> Wow, such debate of terminology
> Just to clarify, I believe the following is correct:
> 
> Due to post processing or the exposure triangle; 99% of the photographers state exposure includes three aspects, shutter speed, aperture and ISO.
> ...


1. Could we theorize that all of them are wrong?
2. There is no such thing as "photons" except in SciFi.
3. Film sensitivity is fixed by the manufacturer.
4. A digital sensor cannot be made more or less sensitive.  It is fixed at the time of manufacture.
5. Your statement has proved that ISO is not involved in exposure.
6.
7.
8.
9. What you are looking at is the JPEG that your camera's firmware has generated in order to display a viewable image.

Since you are locked into the "exposure triangle", let me add another variable; the light.  So now you have an "exposure square" to learn and pass on to the newbs.  Try not to confuse them.


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## AlanKlein (Oct 29, 2018)

After you explain that exposure is shutter and aperture, to beginners, it's time to let them move on to understand the the triangle since they have to deal with ISO a third element. Beyond this, it's just word games we're playing.


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## Tim Tucker 2 (Oct 29, 2018)

AlanKlein said:


> After you explain that exposure is shutter and aperture, to beginners, it's time to let them move on to understand the the triangle since they have to deal with ISO a third element. Beyond this, it's just word games we're playing.



Unfortunately on a forum we have to use words to create a picture of a concept. It is not a *word game* but us trying to find a different set of words that will trigger a different understanding. That some see this as a word game suggests that they automatically dismiss, or will not consider, thinking of the relationships in any other way.

The biggest problem with exposure is that we use a fixed setting of say 125sec at f5.6 to supply a *value* but exposure is in fact a range of brightnesses that we try to record on a media that has a fixed range that it can record well. In film it was easier to understand in that film had a fairly fixed sensitivity so we could use a calibrated *standard* to align our *average light reading* of the scene to align with the *optimum* range of densities we produced on that film to form an image. Our variations from that calibrated *norm* was where experience and understanding of both light and the media came into effect. This is ASA or ISO.

Again the image is a range of densities produced by the different reactions of the film to different intensities of light, and again 125sec at f5.6 are only the settings we use to ensure that we capture the important parts of the scene well within the range that is optimum for the film to record. The *exposure* of 125sec at f5.6 does not equate to any quantity of light but is simply a measurement of the length of time we expose against the diameter of the hole in which we allow light to pass. It may produce either high or low key, it may produce and image with blocked shadows or blown highlights, the snow may be grey along with the cat... The way we align this reading with the sensitivity of our media is through ISO.

With digital we do not have that *floor* or the minimum amount of light we need to produce a reaction the way we did in film and therefore record a density that becomes the image. So with digital we use ISO as a calibration of *brightness* and is linked to a more complex and predictive version of the *average light reading*, but these are still pre-programmed settings on the camera. But it is important to understand that sensors have a fixed sensitivity and that because there is no minimum *floor* that we can *under-expose* and still record an image. ISO then is just a way of adjusting the brightness of the exposure that you made to produce the same range of brightnesses that you would see if you used the *standard* exposure for the base sensitivity of the sensor (which never changed). You do not adjust the sensitivity of the sensor but simply under-expose it and adjust the brightness of the output (post-process) and add a little noise reduction.

As in my original diagram, photography is based on an understanding that a camera collects and focuses light reflected from a scene on light sensitive media. A good understanding of both the light reflected and the way the media reacts to light is essential in understanding how to manipulate this process. All the exposure triangle does is to echo the way the camera is programmed to make this understanding transparent, that you don't need to understand it but merely *point and shoot an let the automation take care of it*. It explains nothing or gives you any real clue, it merely says *accept that the way we've programmed your camera is correct*.


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## greybeard (Oct 29, 2018)

n614cd said:


> Wow, such debate of terminology
> Just to clarify, I believe the following is correct:
> 
> In digital, noise is defined as invalid or unwanted data. As you increase ISO, you are actually making the sensor more sensitive, however this comes at a cost. The cost is you actually increase noise, thereby reducing the signal to noise ratio.
> ...


No,  as you increase ISO you are either boosting the analog signal from the sensor pre A/D or digitally adding brightness gain post A/D.  Sensors have a noise floor that gets boosted as you increase brightness pre or post A/D.


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## Ysarex (Oct 29, 2018)

n614cd said:


> @Ysarex
> 
> Make sure to include the histogram for each before and after
> 
> Sent from my SM-J737T using Tapatalk



Not sure what you mean or want in the way of a "before" histogram. I recorded 2 CR2 files with my Canon G7 -- camera on a tripod and the same exposure for both. One of those was taken with the camera ISO set to 1000 and the other with the ISO set to 125 (my G7 doesn't have a 100 ISO). Here are your two images with their histograms inset in the upper corner. Right now I'm going to leave it to you to pick out which is which as I have removed the EXIF data -- just for fun. I'll gladly post the photos with the EXIF data but first you sort them and explain what you see that makes it obvious which is which.

I did have to post process the files and some subtle differences remain but I believe these two photos do a good job of demonstrating that *there was no advantage of any value that I got from that ISO 1000 setting.* I can just as easily ignore it and get basically the same photo by leaving the ISO at 125.

I used to use a Fuji XE-2 which truly was ISO invariant and as such raising the ISO provided no value beyond allowing me to get an on the spot JPEG to look at. As far as processing the RAF files the only thing raising ISO did was harmful as it reduced DR. My G7 isn't quite as ISO invariant as the XE-2 but it's darn close and it represents the current trend. My new XT-2 is ISO invariant and most of the newest cameras from Nikon, Sony and Fuji are likewise. We're quickly moving to a point where the only point of raising the ISO is to get a JPEG you can chimp if that's what you need to do.

Sorry I didn't have more time earlier, here's the two photos:

Joe


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## Ysarex (Oct 29, 2018)

n614cd said:


> The inability to effectively adjust the ISO afterwards with software in post processing, means that you must include ISO as you take the picture.



See photos posted above. I'm calling that effective.



n614cd said:


> A long time ago, people may have differentiated between "exposure" and "camera exposure"/"proper exposure";



2011 may be a long time ago for you but I still remember a whole lot of what I did that year (big flood on the Mississippi!). 10th edition The manual of Photography Focal Press 2011:  https://www.amazon.com/Manual-Photography-Tenth-Elizabeth-Allen/dp/0240520378

And this is today: "_In photography, *exposure* is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance_." Underline ISO in that definition and repost it. 



n614cd said:


> however with almost no photographer using or needing to technically define "exposure" as just the light photons hitting the sensor,



Speak for yourself. It helps me to understand how things work and I do a better job when I understand how things work. It's important to my students too because they don't like seeing this:






n614cd said:


> the first adjective (camera or proper) has been dropped from common usage.



It was dropped from common usage long before I picked up a camera and many many many and many more decades before the ET raised it's stupid head. Ilford didn't just recently add "camera exposure" to The Manual of Photography. They did that before I was born as they were dealing with the same issue. And they made sure to add an accurate definition of exposure. Colloquial usage and industry jargon have been with us since the invention of language.



n614cd said:


> Leaving us where we are today, exposure means the triangle.



See industry standard definition above. Who are you that you think you get to change it?

Joe



n614cd said:


> Tim


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## Derrel (Oct 29, 2018)

I never even HEARD of the so-called exposure triangle until well after the year 2000. Seriously. I learned that exposure was Intensity x Duration, with Intensity including the lens f/stop and the brightness level of the light, and duration being shutter-open time. I. Never. Ever. Heard. Of. The. Exposure. Triangle. Until.The Web.Era.

I consider the so-called Exposure Triangle to be bull$h!+. The way it is commonly shown/illustrated is WRONG. Wrong,wrong,wrong,wrong! Why is it wrong,wrong,wrong? Because as shown so often, the so-called Exposure Triangle is illustrated so that ISO 100 gives a clean,crisp picture, with no visible noise, while ISO 1,600 and higher are illustrated as being "awful", and creating "noisy" images. That is WRONG. Wrong,wrong,wrong!!! Period. Wrong!

This thread is filled with half-truths, quarter-truths, outright misinformation, and outdated concepts. And some actual truths. We will have to leave it to every person to pick his or her "truth" from among the misinformation.

If ISO is part of "exposure", what does one make of the new, ISO-invariant sensors? How does one explain the beautiful images made by shooting very "dark" images, and then brightening the images up, in post software, with an ISO-invariant sensor-equipped digital camera? How does one explain the nice images Ysarex shows above, made at ISO 125 and ISO 1,000, in Post #58 above? _Why does the ISO 1,000 image not look like crap--as the so-called exposure triangle would predict?_ If the "triangle" were valid, then the ISO 1,000 image would look like rubbish, and it would be VERY obviously different from the ISO 100 image--yet, the two images are visually, for all intents, identical. Now, to me, if a theoretical model does not produce the results predicted by the model, then that hteoretical model is bull$h!+.

I for one do NOT consider that "exposure" means any type of triangle....the definition of "exposure" is well over 100 years old. This triangle concept is internet-era nonsense.

*Equivalent camera exposure settings, *for either one ISO in use, or for different ISO values...now that concept, the concept of equivalent camera exposure settings, that has been around for a long,long time. How a basic, true, proven idea came to be bastardized into this so-called exposure triangle idea...well...that has happened during the Internet era.

Anyway, this thread has drifted very far from the OP's query about why two photos look different...


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## Ysarex (Oct 29, 2018)

n614cd said:


> @Ysarex
> 
> Make sure to include the histogram for each before and after
> 
> Sent from my SM-J737T using Tapatalk



I posted two photos for you earlier that met your criterion and used my Canon G7 which is surprisingly ISO invariant for a little compact. I think they're adequate and refute your assertion but just in case you want to get super fussy as there are some subtle differences I went ahead and hauled my XT-2 out of the closet. The XT-2 is considerably more ISO invariant than the G7 -- in fact for all practical purposes it is fully ISO invariant. Just so you have no wiggle room whatsoever, here's proof you were talkin' nonsense. EXIF data is in place so you can check them. I'm going to post them with links so you can have them at full res and can pixel peep your eyes out if you like. NOTE: I also went ahead and shot a very high contrast scene this time so it pushes limits.

The two histograms:






I don't believe there's any reason to note which one is which.

First photo ISO 100, exposure at f/10 1/2 sec.: ISO_100_xt2.jpg
Second photo ISO 800,  exposure at f/10 1/2 sec.: ISO_800_xt2.jpg

Joe


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## AlanKlein (Oct 29, 2018)

Derrel said:


> I never even HEARD of the so-called exposure triangle until well after the year 2000. Seriously. I learned that exposure was Intensity x Duration, with Intensity including the lens f/stop and the brightness level of the light, and duration being shutter-open time. I. Never. Ever. Heard. Of. The. Exposure. Triangle. Until.The Web.Era.
> 
> ...



The reason it seemed like you never dealt with triangles before 2000, is because you shot film.  With film, you were stuck with the ASA now called ISO of the film.  Once in the camera, there is no way to adjust the speed ISO of a specific film except for pushing and pulling.  If you always shot the same type if film, you never had to change the ASA selection in your might meter.  With digital, the camera has the ability to change the speed of the film now called the digital sensor.  That third selection created the triangle.    Being able to change the ASA of the camera so easily, made the third selection so omnipresent.  Of course, even with film, you had to enter the ASA/ISO of the film to determine the shutter speed and aperture.  If you change the film speed, then you had to adjust that variable in the light meter as well just as you do in a camera.  So even then you dealt with three variables.


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## Ysarex (Oct 30, 2018)

AlanKlein said:


> Derrel said:
> 
> 
> > I never even HEARD of the so-called exposure triangle until well after the year 2000. Seriously. I learned that exposure was Intensity x Duration, with Intensity including the lens f/stop and the brightness level of the light, and duration being shutter-open time. I. Never. Ever. Heard. Of. The. Exposure. Triangle. Until.The Web.Era.
> ...



Been here, done this. From post #32 in this thread in response to AlanKlein: "ISO is important -- never said it wasn't. Above I just confirmed it's needed to get a proper exposure. The problem shows up when you change ISO's roll and try to turn it into an exposure determinant. Read the water faucet analogy in my last post."

From post #31 in this thread in response to WayneF: "You're going to turn on the water and fill a beaker (ISO). You have constant water pressure at the time (scene luminance). The faucet handle is a little special and is equipped with click stops so that you can open it one, two, three, four, etc. clicks and each click opens the value more (aperture). You take an 8 ounce beaker and hold it under the faucet and open it two clicks for 5 seconds (time - shutter speed). The beaker nearly fills. Congratulations! Set that aside. Now reach up on the shelf and grab a 16 ounce beaker. Hold the 16 ounce beaker under the faucet and open it two clicks for 5 seconds. Which beaker has more water in it? The size of the beaker doesn't determine the volume of water."

You say just above: "With digital, the camera has the ability to change the speed of the film now called the digital sensor." *Well no it doesn't.* That's a slight of hand if you will. You're correct that with film we had to deal with the film's light sensitivity. See quote from post #32 just above. Then back to the quote from post #31. You're continuing to try and define "exposure" as "proper exposure." They are two different things and it matters that they be kept separate. A digital camera can't change the light sensitivity of the sensor. It's a fixed constant. With older cameras the analog ISO gain applied to the sensor signal helped to suppress read noise and that was very real. We got better results from an old Canon 5dmkii if we raised the ISO as indicated. We're rapidly moving past that with modern sensors. Look at the two photos in the post #61 just above yours. *ISO is meaningless in those two photos*. If the sensor were actually more light sensitive at ISO 800 it would record further into the shadows -- a higher ISO film would do that. If like film ISO 800 really made the sensor more light sensitive it would have more DR and record both extreme highlights and shadows better than ISO 100. That's not happening in those photos.

I determined the exposure necessary to place the highlight of the lamp at saturation after ISO 800 brightening was applied. I set that exposure and took the photo both with the ISO at 800 and again at ISO 100. Both photos were taken at the same exposure (*shutter speed + f/stop*) and the exposure and only the exposure was responsible for what the sensor recorded. PERIOD! In both images the sensor recorded the exact same data PERIOD because both exposures were the same. ISO was meaningless. ISO 800 did not make the sensor more light sensitive. With virtually no read noise because the sensor is ISO invariant I had the same data to process in both raw files. There is noise in the shadows because of the extreme DR of the photo. *The noise is 100% a function of exposure* -- ISO has nothing to do with it -- noise in both photos is the same because the exposure was the same. The only thing ISO could do for me in that situation is give me a JPEG to chimp from the LCD which I need like I need a hole in the head.

Joe


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## Designer (Oct 30, 2018)

I wonder if the OP is still reading this.


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## n614cd (Oct 30, 2018)

@Tim Tucker 2 

See what happens when I post quickly just before a meeting... 
Correct, changing ISO does not affect the sensor sensitivity. Depending on camera, it affects the gain applied to the analog signal coming off the sensor and/or the digital processor.
As for the rest of your post, umm I do not follow. 

Tim


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## AlanKlein (Oct 30, 2018)

Ysarex said:


> AlanKlein said:
> 
> 
> > Derrel said:
> ...



Legal and technical arguments that are meaningless in the real world.


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## n614cd (Oct 30, 2018)

Designer said:


> Since you are locked into the "exposure triangle", let me add another variable; the light.  So now you have an "exposure square" to learn and pass on to the newbs.  Try not to confuse them.



Nope. I actually never read about it until a couple of recent threads since I am recent member here. Back in roughly 2004, when I decided I to get into digital photography as a hobby I bought a couple book on how digital cameras work, and a second book on image composition. From these I created my own notes, then experimented to learn on my own. Thinking back, one of most hilarious lessons was I got aperture and DoF relationships backwards; so I happily went around taking pictures with my a new DSLR for a year and copied them onto a computer but never actually looked at them on anything larger then the LCD screen on the back of the camera. At the same time, my wife thankfully continued with the point/shoot for images. After about a year, I decided I better start learning about processing the images, and that was when I actually realized I had it completely backwards! I ended up deleting almost every image I took with the DSLR; almost everything was out of focus since I had shot almost everything wide open. I ended up only keeping the ones my wife did with the "cheap" point/shoot!.

Tim


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## Ysarex (Oct 30, 2018)

AlanKlein said:


> Ysarex said:
> 
> 
> > AlanKlein said:
> ...



Oh by all means lets visit the real world. I was asked (friends) to take some photos at an event (no flash please just blend in quietly). Here's one of those real world photos:





That's the JPEG my camera created. I left the ISO at base (200) and to get a fast enough shutter speed for hand-holding I used the EC adjustment on the camera (Fuji XE-2) and set it to -1.67 (EXIF data is in the photo if you want to check). Now be honest; would you have raised the ISO until you had a better "proper exposure" of the gentlemen at the table?

Joe


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## n614cd (Oct 30, 2018)

@Ysarex,

Photo A is the 125 ISO. 
Photo B is the 1000 ISO.

Two points, photo A is slightly larger. A lower ISO in most camera's generates more data, so even when reducing with a JPEG you likely end up with a larger file. 
Second, when you zoom into the glass jar and look at metal hinge, image A has a slightly more pixelated image.

As for the before after, my assumption was you would take two pictures with the same aperture and shutter speed just changing the ISO. Then "brighten" the lower ISO via post processing to be the same rendered level; and include the histograms.  I know with older cameras (such as I have with a Canon 6D), the ISO affects the raw data output. As you pointed out, more and more cameras seem to be headed in the direction of invariant ISO in terms of raw data.

Tim


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## Ysarex (Oct 30, 2018)

n614cd said:


> @Ysarex,
> 
> Photo A is the 125 ISO.
> Photo B is the 1000 ISO.
> ...



You got them reversed. Photo A is ISO 1000 and Photo B is ISO 125. And I'll take that as proof that your original assertion is incorrect. It may have been -- it isn't now. Make sure and have a look at the two photos I posted for you from my XT-2 which is more ISO invariant than the G7. They're a much closer match. In this set you can't argue that use of ISO 1000 was needed or that it provided any value. You can't tell them apart.

I would never try this with a Canon 6D,  I used to shoot 5Ds before I upgraded to Fuji. Those Canons were anything but ISO invariant. It remains true that ISO affects the raw data -- absolutely. Increasing ISO reduces DR and that can be very meaningful. Interestingly although it's usually not an issue, when it is, it's typically not desirable.

Joe

EXIF data intact:


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## n614cd (Oct 30, 2018)

Ysarex said:


> I posted two photos for you earlier that met your criterion and used my Canon G7 which is surprisingly ISO invariant for a little compact. I think they're adequate and refute your assertion but just in case you want to get super fussy as there are some subtle differences I went ahead and hauled my XT-2 out of the closet. The XT-2 is considerably more ISO invariant than the G7 -- in fact for all practical purposes it is fully ISO invariant. Just so you have no wiggle room whatsoever, here's proof you were talkin' nonsense. EXIF data is in place so you can check them. I'm going to post them with links so you can have them at full res and can pixel peep your eyes out if you like. NOTE: I also went ahead and shot a very high contrast scene this time so it pushes limits.
> 
> ....
> I don't believe there's any reason to note which one is which.
> ...



Sorry for the slow reply, after posting yesterday and going into a meeting I have been way to busy to respond. Did I get it right? 

That is really neat. A five minute look, I could not tell. Very cool! Nice to see what is going on with newer cameras.
I think the only point we disagree on, is I am not going to fight the tide about what most people call "exposure" 
I know what it is technically, and I know what a lot of photographers mean by it. 


Tim


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## n614cd (Oct 30, 2018)

@Ysarex 

ack,  I was looking at upgrading my gear the past few weeks (which is how I found this forum) and I decided against it for now. The reality, for the pictures I take now (landscape, vacations stuff, family, friends....) my Sigma lenses and Canon 6D are "good enough" (ok, my older kit lenses suck), and I was planning to wait till some point next year when the mirrorless market might start to shake out a bit.

Then I read about the invariant ISO sensors, and look at the image from the Fuji....


Tim


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## Ysarex (Oct 30, 2018)

n614cd said:


> Ysarex said:
> 
> 
> > I posted two photos for you earlier that met your criterion and used my Canon G7 which is surprisingly ISO invariant for a little compact. I think they're adequate and refute your assertion but just in case you want to get super fussy as there are some subtle differences I went ahead and hauled my XT-2 out of the closet. The XT-2 is considerably more ISO invariant than the G7 -- in fact for all practical purposes it is fully ISO invariant. Just so you have no wiggle room whatsoever, here's proof you were talkin' nonsense. EXIF data is in place so you can check them. I'm going to post them with links so you can have them at full res and can pixel peep your eyes out if you like. NOTE: I also went ahead and shot a very high contrast scene this time so it pushes limits.
> ...



I have no delusions that I'm going to banish stupid from Youtube or escort the ET out behind the barn from whence it will not return. I know what most photographers think they mean when they say "exposure." I however have the official responsibility to be guardian of the truth. I get a paycheck for it. And contrary to what Alan claims understanding the distinction here and knowing how these things actually work does translate into the real world of taking photos.

Joe


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## AlanKlein (Oct 30, 2018)

Ysarex said:


> Oh by all means lets visit the real world. I was asked (friends) to take some photos at an event (no flash please just blend in quietly). Here's one of those real world photos:
> 
> View attachment 165179
> 
> ...



Without knowing the aperture and shutter settings, I would have no way of answering your question intelligently.


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## n614cd (Oct 30, 2018)

Ysarex said:


> I have no delusions that I'm going to banish stupid from Youtube or escort the ET out behind the barn from whence it will not return. I know what most photographers think they mean when they say "exposure." I however have the official responsibility to be guardian of the truth. I get a paycheck for it. And contrary to what Alan claims understanding the distinction here and knowing how these things actually work does translate into the real world of taking photos.
> 
> Joe



Here you go: xkcd: Duty Calls
I also tilt at windmills occasionally. Not as often as when i was younger, I am getting even more cynical as I age (and most think I am cynical enough). 
Good luck, I have gone back and read Alan's post a few times and I still cannot follow what he is postulating. Or at least I cannot reconcile it with what I know.

Tim


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## AlanKlein (Oct 30, 2018)

Ysarex said:


> n614cd said:
> 
> 
> > I have no delusions that I'm going to banish stupid from Youtube or escort the ET out behind the barn from whence it will not return. I know what most photographers think they mean when they say "exposure." I however have the official responsibility to be guardian of the truth. I get a paycheck for it. *And contrary to what Alan claims understanding the distinction here and knowing how these things actually work does translate into the real world of taking photos.*
> ...



Joe, Below is the link for my photos.  Where is yours?


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## Ysarex (Oct 30, 2018)

n614cd said:


> @Ysarex
> 
> ack,  I was looking at upgrading my gear the past few weeks (which is how I found this forum) and I decided against it for now. The reality, for the pictures I take now (landscape, vacations stuff, family, friends....) my Sigma lenses and Canon 6D are "good enough" (ok, my older kit lenses suck), and I was planning to wait till some point next year when the mirrorless market might start to shake out a bit.
> 
> ...



There's a whole new crop of amazing sensors coming on line right now and primarily showing up in Nikon, Fuji and Sony gear. Watch Bill Claff's data. Look at this graph for the new Nikon D500:

Photographic Dynamic Range versus ISO Setting

See that break (dog leg) in the graph at ISO 400. You want to watch for that sensor. Here it is again in the graph that indicates ISO invariance:

Shadow Improvement of Photographic Dynamic Range versus ISO Setting

The straighter that line the more ISO invariant the sensor.

That dog leg is a new feature that Sony bought from Aptina. The sensor is dual impedance. The best way to think of it is it's two sensors in one. At base ISO up to the dog leg channel A is read then at all ISOs above the dog leg channel B is read. In my Fuji the dog leg is at ISO 800. Fuji sets the base ISO at 200 while Nikon sets it at 100.

So to use my Fuji I do have to switch between at least ISO 200 and 800. The second impedance channel is optimized for the higher ISOs and I'm going to tell you I can shoot this camera at ISO 12,800 and you'd be amazed what I can get from it (see below). Now just to make the point I can get the same result as long as I got the ISO above the dog leg.

Joe


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## n614cd (Oct 30, 2018)

AlanKlein said:


> Joe, Below is the link for my photos.  Where is yours?



Did you mess up the quotes? Are you talking to @Ysarex  or me?
I do not have a public page hosting my images anymore.

Tim


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## Ysarex (Oct 30, 2018)

AlanKlein said:


> Ysarex said:
> 
> 
> > Oh by all means lets visit the real world. I was asked (friends) to take some photos at an event (no flash please just blend in quietly). Here's one of those real world photos:
> ...



They're in the EXIF data that's why I mentioned it. 1/140 sec shutter speed f/5.6 using a zoom lens that would be wide open here at f/4 and not a good idea to use at f/4.

Joe


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## AlanKlein (Oct 30, 2018)

n614cd said:


> AlanKlein said:
> 
> 
> > Joe, Below is the link for my photos.  Where is yours?
> ...



How could I assess your knowledge if you don't show me what you got?  It's easy to talk a good game.  Where's the practical proof you know what you;re talking about?


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## AlanKlein (Oct 30, 2018)

Ysarex said:


> AlanKlein said:
> 
> 
> > Ysarex said:
> ...



You could lower the EC another stop or so.  Maybe it would be better to slow the shutter by one stop or raise the ISO one stop.  You could also use the RAW image that would give you more play with the shadow slider.  A lot depends on the capability of your camera's DR.


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## n614cd (Oct 30, 2018)

AlanKlein said:


> How could I assess your knowledge if you don't show me what you got?  It's easy to talk a good game.  Where's the practical proof you know what you;re talking about?



Alan,

Hmmm, how to put this since TPF seems like a family forum.... 
I give up, I do not have a polite way to say it....

I did follow your debate with Joe (@Ysarex ). I could not follow your point(s). As I told him... 
As for determining if I know what I am talking about by looking at my images? 
Nothing in this discussion deals with my artistic ability (and the definite lack there of) or my ability to apply the knowledge. 

Tim


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## AlanKlein (Oct 30, 2018)

If flash is not an option,  you could have added more ambient light, possibly the best solution.


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## n614cd (Oct 30, 2018)

Ysarex said:


> There's a whole new crop of amazing sensors coming on line right now and primarily showing up in Nikon, Fuji and Sony gear. Watch Bill Claff's data. Look at this graph for the new Nikon D500:
> 
> Photographic Dynamic Range versus ISO Setting
> 
> ...



Pages bookmarked, I have seen them referenced before but have not dug into them. I guess I have some reading to do....

Tim


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## AlanKlein (Oct 30, 2018)

> Alan,
> 
> Hmmm, how to put this since TPF seems like a family forum....
> I give up, I do not have a polite way to say it....
> ...


Thanks for your honesty.


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## Ysarex (Oct 30, 2018)

AlanKlein said:


> You could lower the EC another stop or so. Maybe it would be better to slow the shutter by one stop or raise the ISO one stop. You could also use the RAW image that would give you more play with the shadow slider. A lot depends on the capability of your camera's DR.





AlanKlein said:


> If flash is not an option,  you could have added more ambient light, possibly the best solution.



That wasn't possible -- all the interior lights were on. I wasn't comfortable with a slower shutter speed. And in that situation you would have raised the camera ISO. That's your exposure triangle methodology. And in the real world raising the ISO would have reduced DR -- that's what it does. You would have ISO clipped the information out the window with the DR reduction that came from raising the ISO. 

So here's a real world example of how applying an understanding of the way the camera works allowed me to take a photo that you would have failed to get if you raised the ISO.



 

Because I didn't raise the ISO I retained the full DR of the sensor and I was able to keep the real world data that you see out the window in my finished photo. And that's a real world example of how you can take a better photo when you understand how the hardware works and can think clearly about it. I got a real world better photo by ignoring the triangle.

Joe


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## n614cd (Oct 31, 2018)

Ysarex said:


> AlanKlein said:
> 
> 
> > You could lower the EC another stop or so. Maybe it would be better to slow the shutter by one stop or raise the ISO one stop. You could also use the RAW image that would give you more play with the shadow slider. A lot depends on the capability of your camera's DR.
> ...


Joe,

This now prompted a thought. I know there is the whole concept of expose to right. As in better to be overexposed by a stop than underexposed.
How does ISO come into play, or does it not?

Tim

Sent from my SM-J737T using Tapatalk


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## AlanKlein (Oct 31, 2018)

Good example Joe. But what do you do with a scene where you don't have the lighter background but just the same lighting throughout? Do you raise the iso? Or, do you keep the iso lower and then adjust the exposure higher in post processing? How do you know which is better, do these examples also depend upon the make of the camera? How do you explain to users of any piece of a camera which is the best way to go?


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## Ysarex (Oct 31, 2018)

AlanKlein said:


> Good example Joe. But what do you do with a scene where you don't have the lighter background but just the same lighting throughout? Do you raise the iso?



Normally yes, raise the ISO. It's good to raise the ISO if you need it, just don't clip diffuse highlights. When you raise the ISO you lose dynamic range. Look at this graph:

Photographic Dynamic Range versus ISO Setting

A Nikon D5600 delivers 10 and 1/2 stops of DR at ISO 100. At ISO 3200 half of that is gone. If you have a high DR scene, losing half the sensor's DR capacity can be a show stopper. With low DR scenes there is no penalty to raising the ISO. The Exposure Triangle doesn't talk about ISO and DR. It talks about ISO and noise and ISO doesn't cause noise, but it sure chops off your DR.

Here's another more extreme example that I set up. First look at this camera JPEG:





(For the sake of the illustration we can't fix the lighting and the subject of the photo is the ornamental chair you can't see right now next to the bookcase.) I have the raw file that created that camera JPEG and I set the exposure so that the highlights out the window would be at sensor saturation at base ISO on the camera (125). I took two photos:





I raised the ISO to an appropriate level to get a decent JPEG of the chair using the same exposure that I had calculated at ISO 125 -- photo on left. OK, so nearly 5 stops of ISO increase whacked off about 5 stops of my sensor DR (comes off the top) and even though I processed the raw file the highlights in the curtains and out the window are nuked to h*ll. That's ISO clipping and it clips DR from the top. On the right you see the result of processing the raw file that produced that camera JPEG above. Without ISO clipping I had all the data the sensor could record.

And here's the big critical bottom line: They're both the same exposure, 1/8 sec at f/6.3. The exposure and only the exposure determines the data the sensor records if *(BIG IF) the sensor is ISO invariant*. Coming in after the exposure, a raised ISO takes data off the top but if there's no penalty for leaving the ISO at base with an ISO invariant sensor I can have all the data.

Some of the advances we're seeing are in fact breathtaking. I think what we're looking at above is breathtaking. I could never have done that with Tim's Canon 6D or my old 5Dmkii and here I am pulling it off with a $500.00 pocket compact ten years later. The sensors in Canon's older DSLR were very much NOT ISO invariant. They relied on the analog gain to help retain image data on the low end that would otherwise swamp out in read noise.

That image above represents a new capability that our newer cameras are making available. We couldn't do that in the past. ISO invariance is becoming normal. When I bought the G7 used to take the photos above I didn't care that it was ISO invariant. I was surprised when I tested it to find out. I'm happy to use the ISO and typically I do, I raise it as needed. But I also know what the camera is capable of.

So real world: I'm out working in the garden with my wife. I always have the G7 with me. It's evening just as the sun is setting and she says, "hey I want to send a picture to my sister, can you take one from here that shows the yellow zinnias." The sun is setting in a hazy sky and the photo she wants has me looking right at that sunset. I was able to move to get it behind the tree but this is backlight. We all know what happens when we shoot a sunset; the foreground goes silhouette. If she had asked me for a close up of the zinnias I would have raised the ISO, but she wanted the whole garden. So I kept the ISO at base and calculated the exposure to put the sky at sensor saturation. Here's that photo with it's camera JPEG above it.





Very high DR, I can do it if I want.



AlanKlein said:


> Or, do you keep the iso lower and then adjust the exposure higher in post processing? How do you know which is better, do these examples also depend upon the make of the camera? How do you explain to users of any piece of a camera which is the best way to go?



It really does depend on the hardware -- ISO invariance is new for us and it's required to pull this off. It also depends on what you're willing to do in the way of post processing. I'm accustomed to only shooting raw and processing all my photos. Not everyone is and legitimately so. ISO makes camera JPEGs possible and for many people that's critical. If I went to chimp that garden shot above I'm going to look at that JPEG on the LCD and say, "looks good?" It looks horrible! It's all green and underexposed except for the sky which is overexposed. Most people expect to click the shutter and immediately see a decent looking photo. They have to use the ISO function in the camera to do that and they should. I do that too most of the time.

The point in all this that matters for me is that, because I have a proper understanding of how it all works, when my wife asks me to take an impossible photo to send to her sister I can change gears and say, sure -- no problem. Not realizing any other option existed, most people would have taken that garden shot and nuked the sky to h*ll.  I didn't have to.

Joe


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## zulu42 (Oct 31, 2018)

That is a great example Joe posted. These discussions have led me to investigate the ISO invariance of the sensor in my D800. Searches led me to this article:
ISO Invariance Explained - Photography Life
which linked me to this page:
Input-referred Read Noise versus ISO Setting

My own real-world example I'm working in my head is a starry sky shot. I like to open the lens all the way and take 30 second exposures - soaking the sensor with as much starlight as possible. So, looking at the chart for my D800, which I almost understand, I'm thinking I should use ISO 1600 which is the highest actual ISO value before "simulated" ISO value... or is it 6400? Or do I just use base ISO of 100?


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## Ysarex (Oct 31, 2018)

n614cd said:


> Ysarex said:
> 
> 
> > AlanKlein said:
> ...



Great question and another can of worms. The term ETTR is unfortunately troll chum so I'm not going to use it. The pertinent term here we want to use is SNR -- the ratio of signal to noise. With digital we get a straight linear response here: more exposure = better SNR. There's absolutely no downside to that except the pragmatic requirements of taking the photos. It's the age old compromise. We're indoors and the light is dim and we don't want to use flash or a tripod and as a result to hand-hold the camera we have to reduce signal. Our hardware is so bleep bleep good now that we can get excellent quality photos with only 1/10 of the signal our sensors are otherwise capable of. Go back and look at that ISO 12K image I posted from my XT-2. Pragmatically I will tell my students that if maintaining a specific shutter speed is the critical factor then set and lock that shutter speed and put the camera on auto ISO. They complain that they were taught to never use auto ISO. Always try to keep the ISO as low as possible is what they were taught. I cuss and tell them to get the bleep photo! Just wanted to say that to maintain perspective.

So SNR is exposure. And here it really matters to say SNR is exposure the way exposure is traditionally defined. SNR is not "proper exposure" the way the ET works. Maximize SNR to the capacity of the sensor and you capture the maximum amount of data and more data is always better than less data. This one is as simple as 2 + 2 = 4.

Some caveats: Digital sensors clip hard. It's a concrete wall and there's no give if you hit it. So if maximum SNR is good, clipping the sensor is bad. In this situation our camera engineers design a hedge into the camera's exposure system. Most people think base ISO refers to the light sensitivity of the sensor -- it doesn't. Base ISO refers to the standard output brightness of the camera JPEG. All of our cameras are to a greater lesser degree designed to deliberately underexpose the sensor. Generally between 1/3 to 1 full stop. If you try to assess that for your camera and work around it you're playing a dangerous game with a concrete wall.

ISO (here I go again) is not an exposure determinant but it certainly changes the data recorded in a raw file if you raise it. Raising ISO boosts, brightens, gains, amplifies, multiplies the data that is being recorded and stored. You read about cameras having a bit depth like 12 bits or 14 bits etc. Most of our cameras now are 14 bits. 2 ^ 14 = 16,384. All our data ends up as numbers. If you record a brightness value and the number the ADC would assign to that brightness value is 300 at base ISO then if you raise the ISO a stop that number is recalculated as 600 and stored. So you see this coming now right -- if you record a highlight value and the number the ADC would assign to that highlight value at base ISO is 6,000 then if you raise the ISO a stop that number becomes 12,000 and if you raise the ISO 2 stops your highlight is clipped because 16,384 is the biggest number you can store. Raising ISO reduces DR.

Go back to the first set of photos I took with the G7 of the fish and jars. My job was to take one photo at ISO 1000 and another at ISO 125 both at the same exposure. To do that I started by calculating the ISO 1000 exposure. Knowing the ISO would be set at 1000 my job was to avoid ISO clipping but get as close as I could to recording maximum data at ISO 1000. That photo had some specular highlights -- look at the front of the jar of dried mushrooms. I allowed those speculars to clip in the ISO 1000 photo. One of the problems I had in making the two photos visually match is that those specular highlights didn't clip in the ISO 125 exposure!

Joe


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## Derrel (Oct 31, 2018)

It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.


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## n614cd (Oct 31, 2018)

Derrel said:


> It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.



Umm.... Based on Joe's vehemence, I think he would state it was never valid. And he really does have a point, and I am glad he decided to tilt at this particular windmill.
Now the question is if my self control can keep my wallet in my pocket or if I am going to be ordering a new camera soon....

Tim


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## n614cd (Oct 31, 2018)

Joe (@Ysarex )

Technique questions. You talked about maximizing the DR range, by finding the clipping point with ISO set to 1000 with fish/jars image. Was the 1000 just a number you picked because of the original posts I made, or was there some other intrinsic value to it? For the garden shot, how did you determine how the settings to maximize the sky exposure looking to recover the garden post process without clipping the sky?

Assuming I follow your lesson accurately, it is nice to see my trial and error actually has some real science behind it. I have found that I get a better image by pushing the exposure to the point where the sky is almost blown, keeping the ISO at 100 and fixing it post process. If the light meter shows more than -2.5, I switch to bracketed shots. Most of the time in LightRoom, if I increase the exposure more than 0.5 I end up with a blown sky. So I am pretty close to the max exposure. So far, I do this all via "guesswork", but I am getting pretty descent at it! Now I wonder if there is repeatable technique I could apply and will serve me better when I switch cameras instead of depending on muscle memory.


Tim


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## Ysarex (Oct 31, 2018)

n614cd said:


> Joe (@Ysarex )
> 
> Technique questions. You talked about maximizing the DR range, by finding the clipping point with ISO set to 1000 with fish/jars image. Was the 1000 just a number you picked because of the original posts I made, or was there some other intrinsic value to it?



Simply your criteria. ISO 100 to 800, on my G7 that's 125 to 1000 -- three stops.



n614cd said:


> For the garden shot, how did you determine how the settings to maximize the sky exposure looking to recover the garden post process without clipping the sky?



One of the biggest benefits of mirrorless cameras as well as the little LCD compacts is live-view histograms and blinkies for exposure feedback. But before going any further there is no substitute for testing your hardware. So both the G7 and the XT-2 have both of those. If you look at the JPEG of the garden shot you'll see that's terribly green. I had the WB on the camera set to unity so that the live histogram would be an accurate read of the raw file exposure. Here's a link: What is UniWB? | byThom | Thom Hogan Since I don't use my camera JPEGs I'll often leave it set there and just ignore the green JPEGs. (Another example of my behaving far outside the mainstream.) I'm usually able to use those tools to pretty much nail the exposure. The other essential tool for post analysis: RawDigger: Raw Image Analyzer | RawDigger



n614cd said:


> Assuming I follow your lesson accurately, it is nice to see my trial and error actually has some real science behind it. I have found that I get a better image by pushing the exposure to the point where the sky is almost blown, keeping the ISO at 100 and fixing it post process.



As Yoda would say, "expose or expose not." SNR = exposure. Everything else drops away from that fact.

So back to perspective: Get the shutter speed you require and the f/stop you require and hope that produces maximum SNR for the sensor. If it doesn't do whatever you can to increase the SNR (ISO can't do that) like flash or tripod etc.. Once you've done that take the photo. Given the kind of awesome hardware we have today don't let an inability to reach maximum SNR stop you from taking the photo. I just walked back from the grocery store. I stopped on the way and took a photo and I had to raise the ISO to 400 because it's a gloomy rainy day.



n614cd said:


> If the light meter shows more than -2.5, I switch to bracketed shots. Most of the time in LightRoom, if I increase the exposure more than 0.5 I end up with a blown sky. So I am pretty close to the max exposure. So far, I do this all via "guesswork", but I am getting pretty descent at it! Now I wonder if there is repeatable technique I could apply and will serve me better when I switch cameras instead of depending on muscle memory.
> 
> 
> Tim



Test your hardware and get a copy of RawDigger

Joe


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## zulu42 (Oct 31, 2018)

This is all very beneficial information for me. I really appreciate the discussion.

What about folks who just work with jpegs?  Tria... nope. won't even say it.


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## zulu42 (Oct 31, 2018)

I took a photography class from a professional. He drew the triangle on his white board and I think he even wrote "noise" next to ISO. I legitimately deserve my money back.


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## Ysarex (Oct 31, 2018)

zulu42 said:


> This is all very beneficial information for me. I really appreciate the discussion.
> 
> What about folks who just work with jpegs?  Tria... nope. won't even say it.



Even for folks who only shoot JPEG the triangle remains confusing because it mixes up cause and effect. Consider:

1/250th sec at f/5.6 at ISO 200
1/125th sec at f/8 at ISO 200
1/250th sec at f/8 at ISO 400

Triangle heads are going to tell you that all three of those balance and in fact are equivalent exposures producing images that are subtly different in rendition of DOF, noise and motion stopping. But in fact one of those is exposing the sensor approx. 40% less than the other two and as such is also different in regards to the data captured by the sensor. They are not equivalent exposures. So it can also help JPEG shooters to understand the distinction between the exposure that's responsible for SNR as opposed to the "exposure" that produces normal brightness in their JPEG. The image receiving less exposure has a poorer SNR.

Joe

P.S. Glad you enjoyed the read.


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## photo1x1.com (Nov 1, 2018)

Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice  ), despite it seems "a little" off topic by now.

Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard? 
When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?

I have done some ISO tests a few months ago, that I repeated last week with a different background to better show the difference.



 

I also did an ISO invariance test with ISO400 on my Sony A7III. Reading the conversation, I should have done it at ISO100, or ISO 640 (according to this graph Photographic Dynamic Range versus ISO Setting), is that correct?

Oh yes, and one more question, if somebody would be willing to answer: why is the input-referred read noise in this graph: photonstophotos.net/Charts/RN_e.htm#Sony ILCE-7M3_14 higher for lower ISOs?

For those of you interested, I have uploaded the RAW files here: http://www.amriphoto.com/forum/ISOInvarianceTest.zip
In regard to noise, I feel the ISO400 files keep up pretty well up to pushing them +2EV in Lightroom and comparing them to ISO3200. But to be honest, I do see quite a difference starting at +3EV when pixel peeping. 
So my conclusion is no real surprise: you have to decide when shooting: is it more important for me to have a higher dynamic range or less noise. In the particular case of my orchid, I would have gone with less noise.

I know this is not a scientific test as it was done with (quality though) LED lights, but it should give a good impression. 
Here is a sample - which one do you think is ISO400 +3EV in Lightroom, and which is ISO3200?


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## n614cd (Nov 1, 2018)

photo1x1.com said:


> Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice  ), despite it seems "a little" off topic by now.
> 
> Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?
> When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?



I not native English either. I speak American, just ask my French wife  (I could not resist)
I have only read the sensor primer a couple of times on the referenced site, so let's see if I get this correct. 

ISO Invariant sensor only deals with the raw data. When you look at the raw data, you will see no changes in the dynamic range when you change ISO. It also shows up in a bunch of other graphs that I do not understand yet; except one that I do not recall the name. This second graph is of the expected gain and shows a flat line where the camera switches from analog gain a hybrid involving digital. For an ISO invariant sensor, that graph would be flat as all gain is accomplished via the digital processing afterwards. ISO in this case is only used in the image processing engine to generate the camera JPEG. 

EV in Lightroom is a digital formula to artificially increase the values of the color channels. Similar in concept to the ISO gain you get on a jpeg in an ISO invariant sensor. Since we do not know the formula Adobe has selected, there is no way for us to determine with certainty that a +1 and +3 EV have identical effects on the color channels. Based on my playing around with it previously, I doubt it. As the channel gets brighter, Adobe seems to lose details, soften the image, and which suggests some type of "intelligence" in teh formula that as you push it higher there are differing effects.

The advantage of an ISO Invariant sensor when dealing with raw data, is you keep the maximum dynamic range and data. This has two effects; one it "requires" some form post processing the raw data, two if gives the post processing the maximum data to deal with. Note: the post processing can be in Lightroom or other software, or just the jpeg engine in the camera.

Tim


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## photo1x1.com (Nov 1, 2018)

n614cd said:


> photo1x1.com said:
> 
> 
> > Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice  ), despite it seems "a little" off topic by now.
> ...


@american 
Thanks, Tim! I do understand ISO invariance (well, at least I think so ). But ISO invariance would mean, that there is absolutely no noise produced in camera after the analog amplification process. So it wouldn´t matter whether you let the camera do the digital amplification, or the software. But that´s the ideal case which is not the reality in current cameras it seems. Still people talk about ISO invariance. I´d call it relatively invariant, or you´d have to find some kind of index, like LEDs have cri (Color Rendering Index). Because if you call the current sensors ISO invariant, how would you call the ones in 10-20 years "proper invariant" ? So that´s probably the next chance to create misunderstandings. Just like "exposure", "camera exposure", "proper exposure",...


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## n614cd (Nov 1, 2018)

photo1x1.com said:


> @american
> Thanks, Tim! I do understand ISO invariance (well, at least I think so ). But ISO invariance would mean, that there is absolutely no noise produced in camera after the analog amplification process. So it wouldn´t matter whether you let the camera do the digital amplification, or the software. But that´s the ideal case which is not the reality in current cameras it seems. Still people talk about ISO invariance. I´d call it relatively invariant, or you´d have to find some kind of index, like LEDs have cri (Color Rendering Index). Because if you call the current sensors ISO invariant, how would you call the ones in 10-20 years "proper invariant" ? So that´s probably the next chance to create misunderstandings. Just like "exposure", "camera exposure", "proper exposure",...



An ISO Invariant sensor has no analog gain. It does not mean no noise. 
And yes, we are currently in a transition. Some companies have switched to hybrid ISO with some analog and some digital. Such as when you read the sensor primer, the specific Nixon is a hybrid. I know my Canon 6D is also.
Per @Ysarex there are a few camera's which are sensor invariant, and others which are relatively close. He named a couple of them, but I need to run into a meeting so I cannot go back and dig them out of the thread. 

This transition period is actually the "saving" grace for my wallet right now, and what stopped me from ordering the Canon EOS R so I can keep my same high quality native lenses. Since it looks like I am going to switch systems, I may as well wait....

Tim


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## Ysarex (Nov 1, 2018)

photo1x1.com said:


> Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice  ), despite it seems "a little" off topic by now.
> 
> Not being native English, I again feel the wording could be better. ISO invariance implies to me, that it would make no difference whether I push an image 1EV in Lightroom, or 5EV, which would be "100% ISO invariance". Am I wrong in this regard?



Right. ISO invariance basically means the read noise in the system no longer matters. You get the same result from digitally scaling the data in post as you would get from applying analog gain to the sensor signal prior to ADC.



photo1x1.com said:


> When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?



That's why I like Bill Claff's website and test data as opposed to other sites like DXO. Do we set that standard based on what a machine can measure or on what we can practically see? Bill for example rates your camera's DR capacity at 11.6 stops. DXO rates it at 14.7 -- I believe Bill. In referring earlier to my XT-2 I said it was for all practical purposes ISO invariant. I'm sure there's a machine out there that says it's not ISO invariant. In the end all that matters to me is can I take the photo.



photo1x1.com said:


> I have done some ISO tests a few months ago, that I repeated last week with a different background to better show the difference.
> View attachment 165219
> 
> I also did an ISO invariance test with ISO400 on my Sony A7III. Reading the conversation, I should have done it at ISO100, or ISO 640 (according to this graph Photographic Dynamic Range versus ISO Setting), is that correct?



Correct. Your camera is most certainly not ISO invariant and very ISO invariant both at the same time -- just like my Fuji. Your Sony is fitted with a dual impedance sensor. The sensor has two read channels. You've got ISO invariance in each read channel separately but not across them. Your test here compares the two channels one to the other -- NOT ISO invariant.



photo1x1.com said:


> Oh yes, and one more question, if somebody would be willing to answer: why is the input-referred read noise in this graph: photonstophotos.net/Charts/RN_e.htm#Sony ILCE-7M3_14 higher for lower ISOs?



Dual impedance sensor -- it's really like having two sensors in the camera, one for low ISOs and another one for high ISOs.



photo1x1.com said:


> For those of you interested, I have uploaded the RAW files here: http://www.amriphoto.com/forum/ISOInvarianceTest.zip
> In regard to noise, I feel the ISO400 files keep up pretty well up to pushing them +2EV in Lightroom and comparing them to ISO3200. But to be honest, I do see quite a difference starting at +3EV when pixel peeping.
> So my conclusion is no real surprise: you have to decide when shooting: is it more important for me to have a higher dynamic range or less noise. In the particular case of my orchid, I would have gone with less noise.
> 
> ...



Sorry to do this to you but you need to re-do the test and stay in one or the other of the two impedance channels on the sensor.

Two more concerns with your test data: 1. If you look at all the EV 0 exposures in RawDigger you're nearly a full stop underexposed (defined in this case as reaching sensor saturation). 2. Sony is notorious for cooking their raw files and slipping in some lossy compression. I don't know specifically about your camera but that may be a factor.

There's another complication to this topic that needs to be considered and that's the external processing software. All raw converters don't take the same approach to what they're doing and it can matter a lot in this regard. How to assign value to this difference is personal so I think both choices are entirely valid. If you've ever spent time programming a computer you know that there can be a huge difference in performance based on math precision. If you really want to keep computer software moving fast make sure all the math stays integer based. Nothing slows down a computer processor like math with floating point numbers.

The above said processing speed is a critical issue for raw conversion software and I believe LR has its thumb on the scale tipping toward speed over precision. You may be quite surprised to compare the same test processed in LR and then again in say C1 or SilkyPix.

Joe


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## AlanKlein (Nov 1, 2018)

Derrel said:


> It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.



Isn't this expose for the highlights just like in chrome films?   YOu then adjust the sahdow using the shadow slider just as before.  The only difference is the better sensors today allow better results.   If you expose for the shadows, the highlights clip.  Same with digital same with chromes.   Raising or lowering the ISO has no effect on the large difference in stops between shadows and highlights.  That's why we use graduated ND filters or DHR.  If the sensor allows a greater range because of it's DR, that's just another advantage of a better sensor.  But settings still have to be adjusted based on a triangle of settings.  I don't see what's changed.  Maybe I'm missing something.


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## AlanKlein (Nov 1, 2018)

If an a variance sensor allows you to keep the iso at 100, let's say, you still work with triangle.  It's like always using 100 ASA (ISO) film.  You still have to set the light meter's ASA(ISO) to 100 to get the other two settings of speed and aperture.


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## photo1x1.com (Nov 1, 2018)

Ysarex said:


> photo1x1.com said:
> 
> 
> > Wow, I thought this thread was dead. Love the conversation (believe it or not, I read it twice  ), despite it seems "a little" off topic by now.
> ...


Thanks, Joe - much appreciated! I redid the test right away. Luckily my orchid wasn´t dead yet.
I exposed it one stop brighter, and used ISO100 and ISO640 for the test. I also checked the images in capture one. Still, starting at +3EV noise starts being pretty visible compared to the higher ISO shot. I didn´t use capture one in a while and was impressed by their noise removal algorithm.
For those interested, here are the RAW-files: www.amriphoto.com/forum/ISOInvarianceTest2.zip

May I refine my question:


Ysarex said:


> photo1x1.com said:
> 
> 
> > Oh yes, and one more question, if somebody would be willing to answer: why is the input-referred read noise in this graph: photonstophotos.net/Charts/RN_e.htm#Sony ILCE-7M3_14 higher for lower ISOs?
> ...


I did know about the dual impendance, having read quite a bit about ISO invariance recently. However, I wonder why the input-referred read noise is higher in lower ISO-regions, I would have expected it the other way around. That confuses me. What exactly is that input-referred read noise?


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## Ysarex (Nov 1, 2018)

AlanKlein said:


> Derrel said:
> 
> 
> > It's a shame that the truth sometimes takes so many words to explain. Joe's two excellent posts above show why the so-called exposure triangle is no longer applicable, now that ISO invariance completely invalidates one of the critical parameters of the so-called exposure triangle.
> ...



Yes.



AlanKlein said:


> YOu then adjust the sahdow using the shadow slider just as before.  The only difference is the better sensors today allow better results.   If you expose for the shadows, the highlights clip.  Same with digital same with chromes.   Raising or lowering the ISO has no effect on the large difference in stops between shadows and highlights.



Raising or lowering the ISO has no effect on the difference in stops in the scene being photographed. It does have an effect on the range of stops that film or a digital sensor can record. With film moving to a higher ISO film *INCREASES* the range of stops you can record. With digital raising the ISO *DECREASES* the range of stops you can record.



AlanKlein said:


> That's why we use graduated ND filters or DHR.  If the sensor allows a greater range because of it's DR, that's just another advantage of a better sensor.  But settings still have to be adjusted based on a triangle of settings.  I don't see what's changed.  Maybe I'm missing something.



The film/sensor difference relative to ISO involves light sensitivity. Different films with different ISO values really are more or less light sensitive. Using film, especially chrome, it's critical to not over or under expose it. Changing ISO with a digital sensor does not alter the light sensitivity of the sensor and *if the sensor is ISO invariant* then it doesn't matter at all if you do this:

1/100 sec f/8 ISO 1600

or this:

1/100 sec f/8 ISO 100

as long as the ISO 1600 shot doesn't clip the diffuse highlights.

If on the other hand you do have a high contrast scene with a range of let's say 9 stops and you're using Wolfgang's Sony camera from a couple posts up you can record all 9 stops of that scene with the camera set to ISO 100 but you can't record those nine stops if you raise the ISO to 1600.

Joe


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## photo1x1.com (Nov 1, 2018)

Ysarex said:


> photo1x1.com said:
> 
> 
> > When would you consider a sensor being ISO invariant? How much would you have to be able to drag the exposure slider without adding anything unwanted (noise - or what you would call it, color shift,...) to call a sensor ISO invariant?
> ...


BTW: these words surprise me quite a bit


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## photo1x1.com (Nov 1, 2018)

n614cd said:


> photo1x1.com said:
> 
> 
> > @american
> ...


Tim, the analog gain remains no matter if a sensor is ISO invariant or not (if I´m not totally wrong), because it is done before analog is converted to digital (which is essential in digital photography).


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## Ysarex (Nov 1, 2018)

photo1x1.com said:


> Ysarex said:
> 
> 
> > photo1x1.com said:
> ...



Could be a difference in Sony's cooked raw files?



photo1x1.com said:


> I didn´t use capture one in a while and was impressed by their noise removal algorithm.
> For those interested, here are the RAW-files: www.amriphoto.com/forum/ISOInvarianceTest2.zip
> 
> May I refine my question:
> ...



Time to ask Bill -- I know why the difference is there but I'm not able to explain further.

Joe


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## photo1x1.com (Nov 1, 2018)

Thanks, Joe - I appreciate the time you have put into this matter!


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## Ysarex (Nov 1, 2018)

photo1x1.com said:


> Ysarex said:
> 
> 
> > photo1x1.com said:
> ...



A couple times in this thread I stuck in a paragraph and used the word perspective. This makes me think of Derrel who posted a couple times in this thread. He does a good job of keeping perspective. It's too easy to nerd out on this stuff to the detriment of getting the photo. Always place getting the photo as the highest priority.

Joe


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## Ysarex (Nov 1, 2018)

AlanKlein said:


> If an a variance sensor allows you to keep the iso at 100, let's say, you still work with triangle.  It's like always using 100 ASA (ISO) film.



It's like always using ISO 100, 200, 400, 800, 1600, 3200 film all at once in every photo. The point of ISO invariance is you can ignore ISO entirely and that means you can ignore the light meter settings as long as you're within the rough range of those 5 stops between 100 and 3200.

You raise ISO on a digital camera when you can't get the other two settings you want -- typically a fast enough shutter speed. If you raise the shutter speed you're going to expose less. ISO invariance means you can go ahead and do that, raise the shutter speed to where you need it and ignore changing the ISO because it doesn't matter. Just change the shutter speed and keep shooting. You'll expose less but there's no need to bother with the ISO because you're going to get the same photo if you leave it at 100 or raise it to 800. Just take the photo since the ISO doesn't matter.

Joe



AlanKlein said:


> You still have to set the light meter's ASA(ISO) to 100 to get the other two settings of speed and aperture.


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## photo1x1.com (Nov 1, 2018)

Ysarex said:


> Time to ask Bill -- I know why the difference is there but I'm not able to explain further.
> 
> Joe


Wow, Bill replied really quick - here is his answer:

_Input-referred Read Noise always drops as you increase amplification.
This is true of all cameras.



The big drop at ISO 640 is where High Conversion Gain (HCG) on this dual conversion gain sensor begins.
The drop above ISO 51200 is due to Noise Reduction (NR)._


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## Ysarex (Nov 1, 2018)

photo1x1.com said:


> Ysarex said:
> 
> 
> > Time to ask Bill -- I know why the difference is there but I'm not able to explain further.
> ...



Bill is awesome! We should all stop by periodically and leave a thank you note.

Joe


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## n614cd (Nov 1, 2018)

photo1x1.com said:


> Tim, the analog gain remains no matter if a sensor is ISO invariant or not (if I´m not totally wrong), because it is done before analog is converted to digital (which is essential in digital photography).



A truly ISO invariant sensor would have no variable analog gain. Based on what I have seen, such a sensor does not yet exist.
However, there are more sensors which are getting closer and only have limited number of steps.

Reminder, I am new to this level of detail so I am doing discovery! So do not take what I state as gospel!

Tim


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## AlanKlein (Nov 1, 2018)

The issue about using the triangle to determine exposure came up before invariant sensors.  Since 99.9% if cameras are not invariant, then you still need to enter the appropriate ISO.  If not, what am I missing?


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## Overread (Nov 1, 2018)

Even with an ISO Invariant sensor most photographers will still err toward proper exposure in camera. It provides the best way to review the shot on the back and honestly its FAR more pleasing to sit down and tweak an already good shot than it is to have to adjust everything on a black disaster. Sure the invariance gives you FAR more leeway, esp in difficult or very shifting lighting conditions; but I'd wager even with magical sensors we'd still mostly aim for correct in camera exposure.


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## Ysarex (Nov 1, 2018)

Overread said:


> Even with an ISO Invariant sensor most photographers will still err toward proper exposure in camera. It provides the best way to review the shot on the back and honestly its FAR more pleasing to sit down and tweak an already good shot than it is to have to adjust everything on a black disaster. Sure the invariance gives you FAR more leeway, esp in difficult or very shifting lighting conditions; but I'd wager even with magical sensors we'd still mostly aim for correct in camera exposure.



Of course. Nowhere in this thread has anyone made a suggestion otherwise. I took a photo yesterday and posted it here earlier this afternoon. :White on Red I set the ISO before I took the photo for the very reasons you note.

Joe


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## Ysarex (Nov 1, 2018)

AlanKlein said:


> The issue about using the triangle to determine exposure came up before invariant sensors.  Since 99.9% if cameras are not invariant,



That depends on how you're going to define ISO invariance. You can have a machine measure it and get your figure above or you can measure it visually like this guy did and get a pretty good list of cameras: ISO Invariance: What it is, and which cameras are ISO-less

Fortunately you have an opportunity in this thread to back up your 99.9% figure by going to post #61 in this thread: Need help with exposure question and explaining what to look at in those two photos that makes it obvious why the ISO 100 photo (underexposed 3 stops) is worse than the ISO 800 photo that was "properly exposed." If you can't do that then your 99.9% figure is bogus as far as real world usage is concerned.



AlanKlein said:


> then you still need to enter the appropriate ISO.  If not, what am I missing?



Can't imagine. Something about still not understanding why the Exposure Triangle is wrong and confuses people?

Joe


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## AlanKlein (Nov 1, 2018)

Ysarex said:


> AlanKlein said:
> 
> 
> > The issue about using the triangle to determine exposure came up before invariant sensors.  Since 99.9% if cameras are not invariant,
> ...



Then set your ISO at 100 for all shots and let it rip.


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## n614cd (Nov 1, 2018)

AlanKlein said:


> Ysarex said:
> 
> 
> > AlanKlein said:
> ...


Actually for years with Canon 6D, I have found ISO 100 with the image under exposed according to the JPEG to be the best when post processing. I only raise the ISO when the combination of shutter and aperature cannot get within 2 EV of optimal.

I just never understood why until now...

Tim

Sent from my SM-J737T using Tapatalk


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## n614cd (Nov 1, 2018)

Anyone have any idea how the Sigma Foveon Sensor handles ISO? I like the concept of the technology,  but since it is from a small company not sure it can really compete....

Tim

Sent from my SM-J737T using Tapatalk


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## AlanKlein (Nov 2, 2018)

How do you know when to raise the iso because you need it verses when you can allow the exposure to be darker and not raise the ISO? When do you ignore when the light meter is telling you?


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## Ysarex (Nov 2, 2018)

AlanKlein said:


> Ysarex said:
> 
> 
> > AlanKlein said:
> ...



I did. I bought a Fuji XE-2 in November of 2013. It took me 7 months to figure it out, do the testing and to actually develop enough confidence in the camera being functionally ISO invariant, but in July 2014 I made the switch. I remember the photos. here they are:




 

For the first couple months I used the camera adjusting ISO as needed. But I knew I had purchased a camera that was supposed to be ISO invariant so I started testing it. I had just finished a series of tests when I took this photo. After taking the photo on the left I decided I wanted to take it again at a smaller f/stop. Given the shutter speed that meant raising the ISO but I had just run tests to convince myself that ISO on this camera didn't do anything of real value and instead of raising the ISO I turned the EC dial instead. On the XE-2 it was faster and more direct to turn the EC dial to change the exposure. That was it. I kept the camera until May of 2016 and never changed the ISO again. Anytime I needed a different EV for a photo I just turned the EC dial.

Now here's two questions for you: Are you ever going to come up with an answer about the two photos noted above in post #61? What can you see that's different in the ISO 100 photo that separates it from the ISO 800 photo?

And a related question: Here's a 100% enlargement of a section of both photos above in this post.



 

The one taken with the EC set to -2 (EV 13) has noticeably more noise than the one taken at EC +.3. Isn't the noise supposed to be the same since they were both shot at ISO 200?

Joe


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## Ysarex (Nov 2, 2018)

AlanKlein said:


> How do you know when to raise the iso because you need it verses when you can allow the exposure to be darker and not raise the ISO? When do you ignore when the light meter is telling you?



Most people decide to raise ISO when they can't get a fast enough shutter speed to either take a hand-held photo or stop action in the subject. A faster shutter speed reduces exposure. If you can't compensate for the reduced exposure from the shutter speed by changing the f/stop then you have to settle for the reduced exposure.

If your camera is not ISO invariant and/or
If you want a well-exposed JPEG to view and use:
You have to raise the ISO to brighten the reduced exposure.

If your camera is ISO invariant and
You couldn't care less about the JPEGs created by the camera:
You can just reduce the exposure and ignore the ISO setting.

Reducing exposure reduces SNR. Raising ISO does not compensate for the SNR loss. In a non-ISO invariant camera raising ISO can prevent shadow data loss from swamping in read noise.

As for ignoring the light meter, I use the light meter in my cameras but I almost never take a photo with the EC on my camera set to 0. 

Joe


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