# The ISO argument



## PaulR70 (Apr 2, 2019)

I have followed this argument elsewhere so I decided to share my thoughts. One of the arguments is that ISO has nothing to do with exposure!  For the sake of the argument do this test, if you have camera like a DSLR or any digital camera that can be set manually do this. Set the camera up on a tripod, set camera for manual, set ISO to 200, then set the shutter and aperture to get a good exposure and take a shot. Set ISO to 100 do not adjust shutter or aperture take the shot. Set ISO to 400 again do not adjust shutter or aperture and take the shot. Then tell me if it does not effect exposure!
I have three shots out my front window and the only thing  I did in my software was to save them as JPEG's (I shot them in RAW format)


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## Ysarex (Apr 2, 2019)

PaulR70 said:


> I have followed this argument elsewhere so I decided to share my thoughts. One of the arguments is that ISO has nothing to do with exposure!  For the sake of the argument do this test, if you have camera like a DSLR or any digital camera that can be set manually do this. Set the camera up on a tripod, set camera for manual, set ISO to 200, then set the shutter and aperture to get a good exposure and take a shot. Set ISO to 100 do not adjust shutter or aperture take the shot. Set ISO to 400 again do not adjust shutter or aperture and take the shot. Then tell me if it does not effect exposure!
> I have three shots out my front window and the only thing  I did in my software was to save them as JPEG's (I shot them in RAW format)View attachment 171039View attachment 171040 View attachment 171041



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.

That's the standard definition of "exposure" set and finalized in our industry long before you were born. It has not changed in nearly 200 years. In the clause that begins with "as determined by..." please underline ISO for us.

It does matter and for good reason -- I have to go out right now but I'll be happy to explain it to you later. In the meantime you can look at these two photos; both the same exposure 1/6 sec. f/4 but one at ISO 1000 and the other at ISO 125. See the difference?

  

Joe


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## Derrel (Apr 2, 2019)

Ysarex said:


> [>>SNIP>>>look at these two photos; both the same exposure 1/6 sec. f/4 but one at ISO 1000 and the other at ISO 125. See the difference?
> 
> View attachment 171044 View attachment 171045
> 
> Joe



The two photos look quite similar to me.

Could you elucidate on the importance of using ISO 125 as opposed to ISO 1,000?


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## Richard Hutchings (Apr 2, 2019)

I don't see _any_ difference?


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## Soocom1 (Apr 2, 2019)

OK so were doing this again. 

First some parameters: 

ISO is an acronym for International Organization of Standards.   
ISO - International Organization for Standardization

ISO being standards found in every industry including photography, medicine, government, etc. 
ISO9000 is specific to manufacturing. 
ISO for photography is a MEASUREMENT for light values. Ergo: STANDARDS. 


ISO in film is wholly different for ISO in digital. 
They represent the same thing... MEASUREMENT OF LIGHT. 

The arguments recently made on ISO (in regards to photography) is mostly based on the arguments made by individuals who want to talk. 

The arguments are akin to red cars are faster.  

Its nonsensical. 

But for the sake of argument, the argument of itself is based no the ability to modify the exposure based on modifying aspects of a program to achieve the same results. 
ironically, the actions taken though digital and electronic in nature is the same as taken when one over or under exposes silver paper under an enlarger. Achieving the same results. 

Its all a matter of understanding what exposure, light intensity and value are.


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## Derrel (Apr 2, 2019)

Richard Hutchings said:


> I don't see _any_ difference?



MOST viewers would, I wager, tend to agree with that...


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## Soocom1 (Apr 2, 2019)

Oh I can see it, but you have to have a trained eye for it.


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## Richard Hutchings (Apr 2, 2019)

Please train me I did notice a highlight on the jars in one of them.


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## Soocom1 (Apr 2, 2019)

There is an extremely tiny variation in contrast, saturation and grain/pixilisation. 

But you wont see it unless you focus away from the images and switch back and forth between them.


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## vintagesnaps (Apr 2, 2019)

Now I see it, I had to click on each to enlarge and take my glasses off to see them closer. 

So, there's a difference, are we done with this now?? lol


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## Soocom1 (Apr 2, 2019)

lets go back to the core of this whole ISO argument: 
The SENSITIVITY of the capture medium (film or digital) to the light. 

The original DIN numbers and then ASA were based on and intended to make a STANDARD for the sensitivity of film. 

That sensitivity is based wholly on the size of the silver halide crystals. The larger the crystals, the faster the film. 
But it also meant grainier film. 

In digital its not size as it is the ability to record the light intensity striking the pixels as based on a mathematical computation. 

The who intent of the ASA/DIN/ISO number was to make UNIFORM the ability to know what the sensitivity was of the film and the appropriate scale to set one's aperture and shutter speed to.

In digital the faster the ISO (ergo 125 v 1000) typically means more "noise" or pixles that infer the light intensity differently from one setting to another. 
This can all be changed later in post processing, but it has essentially the same effect and "grainy" film.  

The ISO number for film was standardized for good reason. Because those rules DO NOT apply to digital, the numbers become arbitrary and defined by the manufacturer. But typically is in close proximity to film so that photographers have a basis to work from.


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## PaulR70 (Apr 2, 2019)

I started this thread but I did not intend for it to become some long drama! I have been doing photography as a hobby off and on since 1968 and I understand some of differences between film and digital. I just understand that ISO can effect exposure in the digital camera period. Yes I am done with it!


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## JonFZ300 (Apr 2, 2019)




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## The_Traveler (Apr 2, 2019)

I put one over the other in PS and set the layer properties as 'difference'
the difference is more visible on screen (obviously)


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## Ysarex (Apr 2, 2019)

PaulR70 said:


> I started this thread but I did not intend for it to become some long drama! I have been doing photography as a hobby off and on since 1968 and I understand some of differences between film and digital. I just understand that ISO can effect exposure in the digital camera period. Yes I am done with it!



You're operating with a colloquial definition of exposure in which you mean how light/dark is the final image. That's not our industry's standard definition of exposure but it is arguably a popular common usage definition. The two definitions conflict. It matters because what data you record in your photo and the characteristics of that data are a function of exposure as I defined it. If you mix ISO in there you can start getting confused like folks for example equating higher ISO with more noise and claiming ISO is the cause. That relationship is spurious and not causal. I'm going to guess that you likewise believe then that raising the ISO on your camera makes the image noisier. So then how do you explain this photo shot at ISO 12800 on an APS sensor camera: socks?

You're right that ISO is closely related to exposure so it's a subtle distinction. When we change ISO on our cameras the camera's meter system is effected and calculates a new exposure. If we allow the meter to determine exposure then ISO is certainly playing a critical role. But it remains exposure that determines what we're going to capture or not. ISO's functions post exposure in the camera's electronics and software can only cause a loss of information if we allow it.

There's little harm in continuing with your definition of exposure -- the Exposure Triangle model is used by lots of people taking successful photos. It works but it will fray at the edges and if you push your camera toward it's edges the misunderstanding can bite you, or rather an insufficient understanding will leave you with a missed opportunity.

Joe


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## Fujidave (Apr 2, 2019)

This will be the last I post in this thread, for me and me only I don`t actually give a damn about iso as if my images are clean and sharp then I`m well happy.


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## Ysarex (Apr 2, 2019)

Soocom1 said:


> OK so were doing this again.
> 
> First some parameters:
> 
> ...



There are in fact close similarities, but an understanding of how they are different can be helpful.



Soocom1 said:


> They represent the same thing... MEASUREMENT OF LIGHT.
> 
> The arguments recently made on ISO (in regards to photography) is mostly based on the arguments made by individuals who want to talk.
> 
> ...



Well the OP in the previous thread was nonsensical -- it's not nonsensical to understand ISO.



Soocom1 said:


> But for the sake of argument, the argument of itself is based no the ability to modify the exposure based on modifying aspects of a program to achieve the same results.



Now that's nonsensical. For starters you can't modify exposure after the fact. That's one of the reasons why it's important to understand what exposure is.



Soocom1 said:


> ironically, the actions taken though digital and electronic in nature is the same as taken when one over or under exposes silver paper under an enlarger. Achieving the same results.



Speechless.

Joe



Soocom1 said:


> Its all a matter of understanding what exposure, light intensity and value are.


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## Ysarex (Apr 2, 2019)

Soocom1 said:


> lets go back to the core of this whole ISO argument:
> The SENSITIVITY of the capture medium (film or digital) to the light.
> 
> The original DIN numbers and then ASA were based on and intended to make a STANDARD for the sensitivity of film.
> ...



 In digital the sensor responds to the light striking it (photons) by generating a scaled response (electrons) which is then read as an analog voltage signal from the sensor. In most cameras when the sensor must be exposed to less than optimum light intensity ISO engages an amplifier that boosts the analog voltage. That is not a mathematical computation.



Soocom1 said:


> The who intent of the ASA/DIN/ISO number was to make UNIFORM the ability to know what the sensitivity was of the film and the appropriate scale to set one's aperture and shutter speed to.
> 
> In digital the faster the ISO (ergo 125 v 1000) typically means more "noise" or pixles that infer the light intensity differently from one setting to another.
> This can all be changed later in post processing, but it has essentially the same effect and "grainy" film.



It most certainly can *not* all be changed later in post processing. ISO makes hard and permanent changes to the data recorded by the sensor.



Soocom1 said:


> The ISO number for film was standardized for good reason. Because those rules DO NOT apply to digital, the numbers become arbitrary and defined by the manufacturer.



Nonsense. All the current manufacturers of digital cameras adhere to the current ISO standard and supply appropriate notice in the EXIF data with the image. No camera manufacturer is defining their own arbitrary ISO standard.

Joe



Soocom1 said:


> But typically is in close proximity to film so that photographers have a basis to work from.


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## Ysarex (Apr 2, 2019)

The_Traveler said:


> I put one over the other in PS and set the layer properties as 'difference'
> the difference is more visible on screen (obviously)
> 
> View attachment 171057



Two different photos taken in sequence and processed separately from two different raw files -- Damn! I did an amazing job of processing them to be alike.

Joe


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## Derrel (Apr 2, 2019)

I was unaware that "the other thread" had been locked at the 12-page stage.


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## Ysarex (Apr 2, 2019)

Derrel said:


> Ysarex said:
> 
> 
> > [>>SNIP>>>look at these two photos; both the same exposure 1/6 sec. f/4 but one at ISO 1000 and the other at ISO 125. See the difference?
> ...



Sorry, I had to go out earlier and didn't have time.

Both photos were taken with the same camera (Canon G7xmkii). The exposure was determined for the ISO 1000 shot and set manually. Then the ISO was dropped back to base (125) and the same manual exposure was taken -- that's important: same exposure. Both raw files were processed to produce the same brightness final image. The G7 has a new ISO invariant sensor with only a .3EV variance over the ISO scale: Shadow Improvement of Photographic Dynamic Range versus ISO Setting 
That means there should be no apparent advantage in read noise suppression from the ISO 1000 analog amplification as compared with digitally scaling the image. Exposure then is the only real determinant of IQ and since the exposure was the same for both I should be able to process them to look the same.

Joe


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## Ysarex (Apr 2, 2019)

Derrel said:


> I was unaware that "the other thread" had been locked at the 12-page stage.



Yep, let's not do that again.... 

Joe


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## vintagesnaps (Apr 2, 2019)

C'mon, keep up Derrel!! lol 

Let's see, 2 pages in 5 hours, that would put us at 12 pages by what time tomorrow...?? nm I'm giving myself a headache.


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## Derrel (Apr 2, 2019)

Ysarex said:


> Derrel said:
> 
> 
> > I was unaware that "the other thread" had been locked at the 12-page stage.
> ...



"The ISO *argument*."
I guess my brain made a subconscious connection.


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## Ysarex (Apr 2, 2019)

Derrel said:


> Ysarex said:
> 
> 
> > Derrel said:
> ...



I believe you made the intended connection -- OP said he'd been following it. It is unfortunately a Sisyphean endeavor.

Joe


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## vintagesnaps (Apr 2, 2019)

OK, 3 pages in five hours...


Edit - I confess, I had to look that one up, my LOL was added later...


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## Ysarex (Apr 2, 2019)

Richard Hutchings said:


> Please train me I did notice a highlight on the jars in one of them.



*Excellent!* You have the best trained eye then. The exposure that was set was determined to place diffuse highlights at ISO 1000. That means specular highlights would be ISO clipped in that raw file and indeed they are. But the ISO 125 shot did not ISO clip those specular highlights and so they retained tone/detail. I deliberately pushed the specular highlights toward clipping in the ISO 125 shot so as not to give it away but I held back enough to leave a clue. One of the real hard effects of raising ISO is an overall loss of DR due to ISO clipping. Avoiding that in certain circumstances is one of the reasons for taking advantage of an ISO invariant sensor.

Joe


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## Derrel (Apr 2, 2019)

Ysarex said:


> *SNIP>* an ISO invariant sensor.
> 
> Joe



SEE: ISO Invariance: What it is, and which cameras are ISO-less


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## DigiFilm (Apr 3, 2019)

https://i.imgflip.com/vspvw.jpg


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## Ysarex (Apr 3, 2019)

DigiFilm said:


> https://i.imgflip.com/vspvw.jpg



Yep, walked along Berra Park this morning: Extra Tourists this week

Joe


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## Derrel (Apr 3, 2019)

"Exposure" vs. "camera exposure settings/parameters"... maybe we should take some time and define those terms more precisely?


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## dennyr (Apr 4, 2019)

Pardon my ignorance, i only know a little about film and basically nothing about "digital" photography....is the point of all this to say that ASA (numbers) in film mean something different than in digital.?
The size and shape of the grain, as it relates to light sensitivity, is a physical attribute.?
But a digital sensor  does not change its sensitivity...like film does. The ASA numbers in the digital world change due to Amplification/Gain of whatever the sensor sees.?


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## Ysarex (Apr 5, 2019)

dennyr said:


> Pardon my ignorance, i only know a little about film and basically nothing about "digital" photography....is the point of all this to say that ASA (numbers) in film mean something different than in digital.?



The OP in this thread was trying to make a point that ISO is a causal determinant of exposure. On top of that is a general misunderstanding of just what ISO is and does in a digital camera. There's a lot on misunderstanding about both and unfortunately even the camera manufacturers feed into it with some of the beginner-focused material they provide.

ISO in film and digital are different. The standards for both provided by ISO are different. However their use in taking photographs is very similar which of course bolsters the misunderstandings.



dennyr said:


> The size and shape of the grain, as it relates to light sensitivity, is a physical attribute.?



It is.



dennyr said:


> But a digital sensor  does not change its sensitivity...like film does. The ASA numbers in the digital world change due to Amplification/Gain of whatever the sensor sees.?



You're first sentence above is correct: a digital sensor does not/can not change its light sensitivity, and yes film really does. Your second sentence needs some work.

In digital ISO does not define the engineering methodology used and so we need to be careful with wording so as not to suggest as much. Amplification/gain is involved in some of the engineering options used but so is what you referred to as "whatever." The ISO standard for digital does not concern itself with the "whatever" of how but only with the end result. There was an older thread a week or so ago that likely started all this: ISO is not real In Digital Camra's and in that thread TimT provided an excellent definition of what ISO is in digital cameras. I'll not presume to do better and so to quote TimT: "ISO on a camera is simply a calibration of the middle grey tone to an RGB co-ordinate."

In digital cameras the ISO value specifies the brightness of the output target sRGB JPEG created by the camera processing software relative to the input.

Here's a short description of what ISO on a digital camera does:

1. It biases the camera metering system. When you change the ISO number on a digital camera the meter responds to that change and recalculates the exposure. If set at ISO 100 your camera meter calculated an exposure of 1/250 sec., f/8 then at ISO 400 it would recalculate an exposure two stops less: 1/250 sec., f/16 or 1/1000 sec., f/8 or 1/500 sec., f/11. Exactly like film.
2. Unlike film the digital sensor can't alter it's light sensitivity. Assume the exposure at ISO 100 of 1/250 sec., f/8 was ideal for the sensor. If you raise the ISO and the meter calculates a reduced exposure then you're reducing the exposure to the sensor. The sensor receives a less than ideal exposure --  it is under utilized. Regardless ISO specifies the required brightness level for the output JPEG created by the camera processing software and so the engineers who designed and built the camera have to deal with the reduced sensor exposure so as to render the required output brightness.
3. As noted implementation is not specified in the standard and the engineers have options. The sensor produces a scaled response to light by generating an electrical voltage. Photons in -> electrons out. More photons in -> more electrons out. That voltage signal from the sensor is analog not digital. One option used by many cameras is to amplify the sensor signal (gain) before it is converted to numbers. The sensor signal is on it's way to the camera's ADC (Analog to Digital Converter). Signal amplification works very well but does require hardware to implement. In recent years the sensor manufactures have gotten so good that some of the benefits of hardware amplification have been rendered moot. It's easier (no hardware) to just multiply the numbers in the ADC and now that's becoming a very common implementation method. Many cameras (both of mine) us a combination of methods. Another method is to just flag the EXIF data with a value for the raw file converter that says brighten image by X amount. All are valid and applied methods under the standard.
4. Consequences: It's always a compromise. Under utilizing the sensor means the SNR drops. That's Signal to Noise Ratio. Full use of the sensor produces the strongest signal and a strong signal gives us the best image IQ. As the SNR drops the image IQ suffers. The image becomes noisy because we're relying on the weaker part of the signal. Most ISO implementations that brighten the signal do so either before or during ADC which means they're hard baked into the raw file. Boosting the signal up then reduces overall dynamic range and so each ISO increase typically means DR decrease.

Take aways: Compared with film digital is awesome. The newest crop of sensors are flat out jaw dropping in what they can produce. I can have either 10 usable stops of good clean data at low ISO or amazingly reasonable barely noisy photos at ISO values of 12800 -- that's six full stops of reduced exposure above base ISO for my camera and I can still get an excellent photo!! Damn awesome!

Joe


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## MTHall720 (Apr 5, 2019)

There is a lot more to this than I had any idea.  As an old film person I had thought getting started in digital that ISO was kind of like ASA.


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## dennyr (Apr 5, 2019)

I get the gist.....  Thank You


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## Ysarex (Apr 5, 2019)

MTHall720 said:


> There is a lot more to this than I had any idea.  As an old film person I had thought getting started in digital that ISO was kind of like ASA.



In practice it can seem very much like film ISO/ASA but under the hood there are some substantial differences. Most notably that you can change ISO on a digital camera with the twist of a dial on a per shot basis.

This thread was started because the OP wanted to provide obvious evidence that ISO in part determines exposure -- a point of common confusion. We live with a "social phenomenon" (not sure what else to call it) in photography that can be a source of confusion. It's a really good thing that photography is practiced by so many people and it is likewise a good and welcome thing that many enthusiasts/amateurs get involved in photo. This large amount of non-professional participation however bolstered by the rapid communication options of the Internet can spread misinformation at an alarming rate (politics?). A term with a specific meaning or a process or phenomenon can become colloquially misunderstood and that misunderstanding can spread so that effectively the term-meaning or phenomenon gets changed. You'll run into the term bokeh at some point if you keep up your interest. What should we do now with bokeh? Should it mean what it originally meant or should we accept what it means now in the minds of the Youtube misinformation hordes?

So "exposure" likewise has a colloquial meaning that deviates from it's formal meaning in our discipline. Colloquially "exposure" means how light or dark your photo appears and when taking a photo with a camera you can alter that light/dark appearance by changing shutter speed, f/stop, or ISO. Therefore the factors effecting exposure must be shutter speed, f/stop and ISO. And then you get this:






(Notice the misuse of the word bokeh in that diagram --  it's a twofer!) The problem with that is ISO doesn't really causally effect exposure. It wouldn't be a big deal if it didn't matter but it does. And it's because it matters that our industry long ago defined exposure differently than the colloquial understanding. Exposure is the amount of light per unit area that strikes the film/sensor. There are three causal factors: the intensity of illumination in the scene, the time of the exposure (shutter speed) and attenuation of the light through the lens (f/stop).

So how does ISO fit in? It's obviously involved. You have to consider it when you make an exposure. Why isn't it a factor then? I explain it in class like this: We're in the lab and I can literally walk over to the sink and do this and I do. Turn on the water and let's call that light coming through the camera. I pick up an 500ml beaker and hold it under the faucet -- that's ISO. Turning the faucet on/off is the shutter speed and how much I turn the faucet is f/stop. Let's assume I can do this with precision. I turn the faucet on for two seconds with a 1/8 turn of the handle. I successfully fill the beaker. How much water do I have? That's the exposure and it's 500ml. Now I switch to a 1 liter beaker and make another exposure. I turn the faucet on for two seconds with a 1/8 turn of the handle. How much water do I have? 500ml just like the last exposure I used the same shutter speed and f/stop. Did changing the volume of the beaker change the exposure? No.

In practice however because ISO does in fact change the light/dark appearance of our final photo and because if we use the camera meter (nearly all of us do) then changing ISO causes the meter to recalculate exposure it certainly seems like ISO is an exposure factor. The triangle diagram above is commonly used and no question it helps beginners get a handle on using the camera. But it muddies the cause and effect of what's going on and that can be bad. Pretty soon you encounter beginners who believe that ISO is the cause of noise in a photo (it's not) and that misconception causes them to alter their behavior using the camera. The primary cause of noise in our photos is reduced exposure. What ISO does in fact tends to suppress noise. So caught up in a misunderstanding (and I see this in class all the time) a beginner resists raising ISO for fear of noise when the ISO function would have in fact made their photo less noisy. Understanding the cause of the noise is the first step in being able to control it.

Joe


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## dennyr (Apr 5, 2019)

This is all new to me, i do not own a digital camera, so i have no idea.
But are you saying...all else equal... there are pictures that have more noise at Iso-200 than Iso-3200.?


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## Ysarex (Apr 5, 2019)

dennyr said:


> This is all new to me, i do not own a digital camera, so i have no idea.
> But are you saying...all else equal... there are pictures that have more noise at Iso-200 than Iso-3200.?



All else is not equal and it would not be possible to take those two photos while maintaining all else equal. It's very unlikely as it would require an atypical use of the camera. It's possible however because the cause of noise isn't ISO directly. The noise we see in digital photos is primarily a function of exposure.

However ISO is indirectly linked to exposure so that when we raise ISO it's because we typically want to (need to) reduce exposure. So ISO is certainly linked to noise because of how we use it.

Let's look at a less extreme example that is typical of what my students do. Here's three photos (I had ginger snaps with my coffee this morning).



 

 



I adjusted them to all appear the same exposure but out of the camera the first was too dark the middle was right and the last was too light. The first is taken at ISO 1600 and in the manner of one of my students it is underexposed. ISO 3200 was indicated by the meter but my students don't want noise so they often resist raising the ISO. They believe the noise comes from the ISO increase. The first two photos are both exposed 1/50th sec. f/4.

Now let's look at the noise in the three photos. This is a 100% enlargement of a section. I have noise filtering in the software turned off for all.





The left photo is taken at ISO 1600 1/50th sec. f/4. The middle photo is taken at ISO 3200 1/50th sec. f/4. The noise is basically the same in both with a very slight improvement showing in the ISO 3200 photo. Typically what ISO does in the camera suppresses noise. My students are making a mistake and they should raise the ISO to the level needed -- the noise is from the exposure. Now the third, the right hand photo has less noise. It's noticeably better and it is also taken at ISO 3200. What's different about the right hand photo is I changed the exposure to 1/20th sec. f/4. It doesn't seem like much but that's more than doubling the amount of light reaching the sensor and it shows. That exposure change however of course highlights the entire dilemma to begin with: and I used a tripod as if I could convince my students to get and use a tripod. 1/20th sec. is not hand holdable -- ISO is often about motion.

So all things not being equal no one is going to reduce exposure for an ISO 200 photo by more than 4 stops to show that it's then noisier than an ISO 3200 photo properly exposed. 

Joe


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## Grandpa Ron (Apr 5, 2019)

It has been my observation that most of the discussion around ISO is more of a lesson in semantics then photography.

We all agree that given a higher ISO; the digital picture picks up noise, the film picture picks up grain.

It is also fairly well established that the switching from a low to high digital ISO, while keeping the proper exposure, introduces some degree of change in the picture, because the electronic are not perfect. So to film, a high ISO film or pushing a low ISO negative during development, does not produce the same result as standard film processing, regardless of the exposure.  This comes as no surprise to those remember the fickle nature of photochemistry.

My point is, this is all a mind game.  We select an ISO that we are happy with, it makes no difference what ISO the other person prefers.

In fact, the choice of ISO is usually dictated by circumstance. We need a high ISO to capture a speeding race car and a slow ISO to blur the image of moving water. However, given the increasing power of post processing, even these old "rules of thumb" are becoming a moot point.

The importance of subtle changes in camera performance is mostly opinion. They have been there forever and will be there forever. I put it on a par with trying to find fly specs in pepper.


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## eja (Apr 9, 2019)

Ysarex said:


> dennyr said:
> 
> 
> > This is all new to me, i do not own a digital camera, so i have no idea.
> ...




So, can a safe take away from this discussion be as follows?

Don't underexpose, since that is the cause of the noise.  It doesn't matter what ISO is set, just ensure you set the correct exposure?


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## Ysarex (Apr 9, 2019)

eja said:


> Ysarex said:
> 
> 
> > dennyr said:
> ...



Expose the sensor as much as possible. That's the bottom line. Everything about IQ improves with more exposure up to the full capacity of the sensor. There are different causes of noise in a digital camera but the dominant noise source is what we call shot noise and that's a function of exposure -- the common noise we see is caused by reduced exposure.

You have to deal with the pragmatic requirements of taking the photo and you should take the photo even if you have to reduce exposure to do so. ISO plays a role in that raising ISO biases the light meter to calculate a reduced exposure and so the correlation that folks see is real but causation is spurious. So if you raise ISO and take the exposure the meter indicates you'll get more noise because you reduced exposure. If you need a faster shutter speed that's going to reduce exposure and that will cause noise.

Whatever the given circumstance, expose the sensor as much as possible.

Joe


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## Grandpa Ron (Apr 9, 2019)

I think the better take way from this discussion is to remember photography is a personal expression. 

It is important to understand the effects of  changes to ISO, depth of field, shutter speed etc. and it is interesting to read others opinions on the subject. It adds to your knowledge base and helps build your photographic techniques for various settings.   

However, whether the picture has too much noise, or too much or too little depth of field, is too soft a focus or a host of other variables;  depends on the person taking the picture.  Even "proper exposure" has some latitude.


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## EventArtist (Apr 9, 2019)

In general, people seem to tolerate noisy/muddy shadows more than blown-out highlights; so, shooting digital is more like shooting slide-film than print-film: if in doubt then (slightly!) adjust to underexpose, don't adjust to overexpose. 

If that bothers you, then bracket your settings until you become more comfortable with your (meter’s) approach to camera settings in your typical lighting conditions. 

• How accurate is your light measurement?

You must decide what’s important in your subject composition, and you should know how (in-)accurate your (meter’s) choice of camera settings may be. 

Ideally, you neither under- nor over-expose; rather, you match the dynamic range of (the important parts of) your subject composition to the dynamic range of the camera—using aperture and shutter (and filters, etc.) to control the *AMOUNT* of light hitting the sensor PLUS using “ISO” to control/bias/adjust the *RESPONSE* to that light by the sensor. 

• Rarely “ideal”?

Things are rarely “ideal” so you have to decide how to “properly” record the “important” parts of your subject composition—and in a rush without bracketing I’d recommend trying for “correct” and leaning toward “under”—an approach which should bring all the (important) parts of your image within */- 1 f/stop, easily within acceptable adjust/burn/dodge range with a lean toward protecting highlights over shadows. 

• Just what works for me. 

Your mileage may vary, depending on how your camera electronics’ ISO “bakes into” a raw file “recording” of the sensor’s response to light. 

Of course, with JPEG files (but not relevant to raw files) beware of your camera’s “high ISO NoiseReduction” and especially any “auto-dynamic” (“Active D-Lighting” etc.) options which can affect your image if you don’t pay attention to what it’s doing to alter your image. 





Ysarex said:


> eja said:
> 
> 
> > Ysarex said:
> ...





Ysarex said:


> eja said:
> 
> 
> > Ysarex said:
> ...


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## Ysarex (Apr 9, 2019)

Grandpa Ron said:


> I think the better take way from this discussion is to remember photography is a personal expression. It is important to understand the effects of  changes to ISO, depth of field, shutter speed etc. and it is interesting to read others opinions on the subject. It adds to your knowledge base and helps build your photographic techniques for various settings.
> 
> However, whether the picture has too much noise, or too much or too little depth of field, is too soft a focus or a host of other variables;  depends on the person taking the picture.  Even "proper exposure" has some latitude.



This is not a thread about personal expression. It's a thread about "how it works." It's not about how much noise is too much noise it's about what causes the noise. I'm sitting here just now listening to James Galway playing the flute. I'll bet he has spent long hours over the course of his life learning to play the flute and practicing playing the flute during which times he wasn't concentrating on how best to express Mouquet's "La Flute de Pan" -- that goes without saying. *In what way does personal expression change "how it works"?*  Those who understand "how it works" are best prepared to manipulate the process for personal expression. That's the point.

Joe


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## Ysarex (Apr 9, 2019)

EventArtist said:


> In general, people seem to tolerate noisy/muddy shadows more than blown-out highlights; so, shooting digital is more like shooting slide-film than print-film: if in doubt then (slightly!) adjust to underexpose, don't adjust to overexpose.
> 
> If that bothers you, then bracket your settings until you become more comfortable with your (meter’s) approach to camera settings in your typical lighting conditions.
> 
> ...



What is *RESPONSE* and in what way does ISO control/bias/adjust the sensor's response to light?

Joe



EventArtist said:


> • Rarely “ideal”?
> 
> Things are rarely “ideal” so you have to decide how to “properly” record the “important” parts of your subject composition—and in a rush without bracketing I’d recommend trying for “correct” and leaning toward “under”—an approach which should bring all the (important) parts of your image within */- 1 f/stop, easily within acceptable adjust/burn/dodge range with a lean toward protecting highlights over shadows.
> 
> ...


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## Braineack (Apr 9, 2019)

PaulR70 said:


> Then tell me if it does not effect exposure!



It doesn't.


What you're asking us to do is the equivalent of this:

I took your photo and lowered the ISO; this is the same image, same shutter speed and aperture.






Tell me ISO doesn't affect the exposure.


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## Soocom1 (Apr 9, 2019)

OK.. So one thing that I was NOT aware of, was that the "native ISO" from the manufacturers may be varied based on manufacturing techniques and materials. (This is akin to the diff. between iron base materials that are used for iron engines from Ford. v. Chevy.)  Oh and please don't read too much into that, its simply a comparison that car guys will understand. 

But they still do effectively the same thing. 

BUT the "native ISO" is a measurement of the sensitivity of the sensor itself and using simple arguments here, if the "native ISO" of a particular camera is say equivalent to 100, then anything below that is akin to filling a bucket and letting the water keep running after it overflows. Your simply loosing the ability to collect and your gaining no advantage.  
At least that's how I am reading this. 

But this is also determined on the A/D converter and bit rate if I read that correctly. 
So, that would mean to me (correct me if I am am wrong here) but if the bit rate was say 256, then an extended low and high ISO would show the same level of noise but the contrast would be substantially wider and moreover, total tonal range would also be more dynamic.


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## Derrel (Apr 9, 2019)

Topic For Round II of "The ISO Argument":  The "best" ISO to set on the ISO dial or LCD panel (with a modern d-slr) is usually not the lowest ISO, but rather is often 200, or 320, or 400, or 500, or 640.

Discuss/argue.


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## Soocom1 (Apr 9, 2019)

Derrel said:


> Topic For Round II of "The ISO Argument":  The "best" ISO to set on the ISO dial or LCD panel (with a modern d-slr) is usually not the lowest ISO, but rather is often 200, or 320, or 400, or 500, or 640.
> 
> Discuss/argue.


I would say fine, but this also tends to lead to another question feeding off my previous post. 
That is, would you *USE* a lower ISO if offered? 
Don't worry about the technical side of things, if you had a 6 ISO setting on the camera would you use it?


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## Derrel (Apr 9, 2019)

I have LONG advocated 320 to 400 as giving the widest "shooting envelope" for the majority of situations. I grew up on ASA 125 B&W, then 400 ASA b&W, then ISO 100 ro 200 color negative film, then ISO 25,64,and 100 color reversal films, etc. One of my earliest d-slrs was the Fuji S1 Pro, which had a *lowest* ISO of 320,and was a terrible daylight flash camera as a result. My feeling is that setting one's ISO at 50,64,80,100, 125,160 area leads to a lot of blurry images,in many situations.

For MOST daylight, hand-held use, I feel that low ISO levels, below 50 let's say, are of limited use. For studio flash use, low ISO values can be of some use, especially with older flash units which are not easily lowered to less than 100 or 200 Watt-seconds.


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## Ysarex (Apr 9, 2019)

Soocom1 said:


> OK.. So one thing that I was NOT aware of, was that the "native ISO" from the manufacturers may be varied based on manufacturing techniques and materials. (This is akin to the diff. between iron base materials that are used for iron engines from Ford. v. Chevy.)  Oh and please don't read too much into that, its simply a comparison that car guys will understand.
> 
> But they still do effectively the same thing.
> 
> ...



So not quite -- this was part of the misconception in the earlier thread a few weeks ago and likewise part of Tony Clickbait's misunderstanding in his recent video. Our camera sensors don't have ISO ratings. Base ISO is not the light sensitivity of the sensor. The ISO standard also explicitly states that the ISO ratings do not apply to raw files. The ISO standards (two different methods used by manufactures to establish the values: SOS or REI) identify a standard brightness level in a SOOC sRGB JPEG relative to the brightness of the scene. That's it and that's all.

The bucket analogy catching water is a good one and absolutely correct that once the bucket is full you stop recording information. The sensor does have a full well capacity and if we exceed that we clip highlights.



Soocom1 said:


> But this is also determined on the A/D converter and bit rate if I read that correctly.
> So, that would mean to me (correct me if I am am wrong here) but if the bit rate was say 256, then an extended low and high ISO would show the same level of noise but the contrast would be substantially wider and moreover, total tonal range would also be more dynamic.



The same exposure shows the same noise regardless of ISO if we're talking about shot noise which we should be. ADC bit depth does not determine dynamic range it determines the how discreetly the data is recorded. Think of two sets of stairs both climbing a hill that is 50 feet high. 50 feet is the dynamic range. One set of stairs has 35 steps and the other has 60 steps -- that's the bit depth variation. Both stairs reach the top, DR, but one is smoother than the other.

Joe


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## zombiesniper (Apr 9, 2019)

Are we really going to dig up the same old arguments and rage another war that WILL NOT MAKE ANYONE A BETTER PHOTOGRAPHER?

Seriously! If you wish to debate trivial facts that are won't make a darn bit of difference to an image please resurrect an old thread the rest of humanity has blocked.



NOBODY has ever won this argument. It's like pushing a rope. Fun to do for a bit but eventually you realize you're getting nowhere.


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## Soocom1 (Apr 9, 2019)

I personally had to take a break from the discussion because of the obtuse direction it was taking. 

But it is worth the discussion because all too often, people do not grasp the specifics of a particular technology. 

Its akin (yes another metaphor) to someone saying that you will go faster in a car with high octane or that we can eventually make a large truck that gets 100 mpg with gasoline. 
Its superfluous in its base without regard to the technical aspects that make the system a discussion of the absurd if those speaking are working from a low level knowledge base. 


i too am guilty of that but it also opens insight to something that may enhance one's knowledge base.


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## zombiesniper (Apr 9, 2019)

My point is if both can get you to the finish line in a fashion that the difference is not discernible to the viewer..........who cares.


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## Soocom1 (Apr 9, 2019)

I think that there are some (including myself) who see the technical side as something that can be exploited if understood. 

I get what your saying. In the end, the universe will go cold and we'll all be dead. 
But for now, this moment, its relevant to those who see something worth pursuing and discussing.


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## wfooshee (Apr 9, 2019)

Braineack said:


> PaulR70 said:
> 
> 
> > Then tell me if it does not effect exposure!
> ...



I like this example. To reinforce the point (or beat the dead horse...) Braineack didn't change the amount of light that hit the sensor to produce the original image, so he did not change the _exposure_. He changed how that exposure was rendered. I think it's an easier point to grasp when you come from years of film, where the so-called "third variable" didn't exist. You exposed for the film you had loaded.

Changing the ISO is a bit artificial when you move from film to digital. It's like cheating, somehow. Let's "pretend" the camera is faster than it is, so we can shoot in this low light without needing 3 seconds of open shutter. Kind of like pushing film...

To the OP, exposure is light on the sensor. The only things that affect exposure are aperture and shutter speed. Adjusting the ISO without adjusting the others changes the rendering, not the exposure. You might call it semantics, but it's an important distinction. If the camera is in an auto-exposure mode, changing the ISO _does_ change the exposure, but it does not change the _rendering_. You're interchanging expose with render.


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## Ysarex (Apr 9, 2019)

Soocom1 said:


> I think that there are some (including myself) who see the technical side as something that can be exploited if understood.



YES!

Understanding how my camera works allows me to exploit that understanding to take better photos, and I do.

Joe



Soocom1 said:


> I get what your saying. In the end, the universe will go cold and we'll all be dead.
> But for now, this moment, its relevant to those who see something worth pursuing and discussing.


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## zombiesniper (Apr 9, 2019)

I fully understand....and applaud exploiting an aspect of photography but when it's done  without the other two sides of the triangle and we don't talk about them.........it's like only starting a fire with heat......................F*&^%ing impossible without fuel and oxygen.

Deal with the WHOLE problem or stay at home.


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## JonFZ300 (Apr 9, 2019)

All you have to do is take the same pic with different ISO settings and pixel peep to see what it does for your camera. I don't understand what all the fuss is about regarding whether it's actually a component of exposure or not. In the end, it's about the images and image quality.

On my small sensor FZ300, it's irrelevant because I never take it off 100 ISO because I notice changes to IQ even at 200 and 400 is just ugly to my eye. 

I'm definitely not anti-learning, but knowing the technicalities and science behind how a camera's ISO function works doesn't change the fact that the only way to exploit that knowledge is to change the ISO setting before taking the picture. And you should know what that does to the image from the test I mentioned above.


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## Derrel (Apr 9, 2019)

I now shoot on an iPhone SE,a Nikon D610, and a Nikon D800. I no longer worry much about ISO level. The ISO is set automatically on the iPhone...and I have No Control over the ISO level...but the program in the iPhone is pretty good.
  In the D610 and the D800, the sensor technology is,for practical purposes, ISo-invariant. The DR is extremely good. I seldom exceed ISO 1,600, and with studio flash, often use Iow ISO values, occasionally resorting to the LOW- values to get the right brightness in JPEG images. I have a lot of (now) overly-powerful studio flash gear that was made back in the days of 25 to 100 for color film.


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## beagle100 (Apr 9, 2019)

Ysarex said:


> MTHall720 said:
> 
> 
> > There is a lot more to this than I had any idea.  As an old film person I had thought getting started in digital that ISO was kind of like ASA.
> ...



seems reasonable
But always I use auto ISO

*www.flickr.com/photos/mmirrorless*


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## Ysarex (Apr 9, 2019)

JonFZ300 said:


> All you have to do is take the same pic with different ISO settings and pixel peep to see what it does for your camera. I don't understand what all the fuss is about regarding whether it's actually a component of exposure or not. In the end, it's about the images and image quality.
> 
> On my small sensor FZ300, it's irrelevant because I never take it off 100 ISO because I notice changes to IQ even at 200 and 400 is just ugly to my eye.



Wow. I have a similar 12 meagpixel compact with about the same size small sensor. I use it up to ISO 1600 and I'm happy with the results. Here's an example:






Sure ISO 80 is better but I don't see the above as ugly.

Joe



JonFZ300 said:


> I'm definitely not anti-learning, but knowing the technicalities and science behind how a camera's ISO function works doesn't change the fact that the only way to exploit that knowledge is to change the ISO setting before taking the picture. And you should know what that does to the image from the test I mentioned above.


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## Ysarex (Apr 9, 2019)

beagle100 said:


> Ysarex said:
> 
> 
> > MTHall720 said:
> ...




And that's one of the things I initially do with my students. They all believe they should set the ISO and keep it as low as possible (bleepin' bleep YouTube). I tell them to put it on auto and let the camera set it. They're much better off paying attention to setting exposure which will really effect their photos.

Joe

*


beagle100 said:



			www.flickr.com/photos/mmirrorless
		
Click to expand...

*


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## JonFZ300 (Apr 9, 2019)

That's a nice looking shot. I shoot mostly birds and stuff outdoors in daylight and the FZ300 is a constant f2.8 through the full zoom range so I never really need to bump the ISO anyway.


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## JonFZ300 (Apr 9, 2019)

Here's my 1600 at full size in an indoor, low-ish light setting:


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## Ysarex (Apr 9, 2019)

JonFZ300 said:


> Here's my 1600 at full size in an indoor, low-ish light setting:



Your camera can save a raw file and should be able to do much better than that. I would expect your camera at ISO 1600 to at least equal what I posted.

Joe


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## JonFZ300 (Apr 9, 2019)

To be fair that's a a screen shot of the unprocessed raw file. Here's a jpeg of the full image after conversion to jpeg and a little bump in exposure in ACR. I guess I stand corrected. It's actually not that bad. The first thing I did when I got the camera was an ISO comparison and I wasn't happy at all. Looking at this, I'm not so upset anymore. It's bad but not that bad. My FZ200 was worse for sure, maybe that's where I got into the low-ISO mindset. Thanks for showing me your 1600 image. Cheers


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## Ysarex (Apr 9, 2019)

JonFZ300 said:


> To be fair that's a a screen shot of the unprocessed raw file. Here's a jpeg of the full image after conversion to jpeg and a little bump in exposure in ACR. I guess I stand corrected. It's actually not that bad. The first thing I did when I got the camera was an ISO comparison and I wasn't happy at all. Looking at this, I'm not so upset anymore. It's bad but not that bad. My FZ200 was worse for sure, maybe that's where I got into the low-ISO mindset. Thanks for showing me your 1600 image. Cheers



That's much better but, It can still be better than that. I suspect at least twice as good. I just stopped over at DPReview and looked over the specs for your camera.

Joe


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## JonFZ300 (Apr 9, 2019)

Ysarex said:


> That's much better but, It can still be better than that. I suspect at least twice as good. I just stopped over at DPReview and looked over the specs for your camera.
> 
> Joe



Well, I'm glad I joined this discussion. This one was taken at ISo 400 and I think it looks pretty good. I opened the blind to let in some natural light. I think I'm still going to stick with 100 for my birds and well-lit stuff but it's good to know that I can use at least 400 and 800 if I need to and maybe even 1600 if I REALLY need to. Thanks again.


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## Ysarex (Apr 9, 2019)

JonFZ300 said:


> Ysarex said:
> 
> 
> > That's much better but, It can still be better than that. I suspect at least twice as good. I just stopped over at DPReview and looked over the specs for your camera.
> ...



I suspect your camera at ISO 1600 can be this good or nearly this good.

Joe


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## eja (Apr 12, 2019)

Ysarex said:


> JonFZ300 said:
> 
> 
> > Here's my 1600 at full size in an indoor, low-ish light setting:
> ...


I'm glad I'm still following this discussion.  IF I'm still following the main points correctly, even a small sensor camera should be able to produce an image at high ISO with acceptable noise if it is exposed correctly.

I've included a picture taken with an older Olympus XZ-1.  I was using off camera flash with the neutral density filter activated on the camera.  That provides about a 3 stop underexposure.  I wanted to underexpose the background, use a wider fstop to try and limit my depth of field.  The flash was an old sb26 off camera.  The image was shot in raw.

Now, I don't know why I ended up at iso 400.  I was planning on using iso 100 so it may have been an accident.  The point is, however, that you can see the image is noisy.  My first thought was it was due to being at higher iso on a small camera with a small sensor.  However, I did purposely underexpose the ambient and then set my Fstop at f 2.0.   The flash exposure on the subject was 3 stops above roughly and measured with a light meter.

Assuming I got my exposure correct on the subject, what would attribute to the visible noise?  Simply camera limits or I most likely didn't get my exposure correct?

The image was processed in DXO with all of the noise reducing stuff and contrast stuff turned off.  It's pretty much out of the camera with only the distortion corrected.


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## Ysarex (Apr 12, 2019)

eja said:


> Ysarex said:
> 
> 
> > JonFZ300 said:
> ...



We need to look at the raw file for your answer. Put the raw file on something like Dropbox and post a link to it here and I'll take a look.

Joe


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## eja (Apr 12, 2019)

Ok, thanks for the reply.  Here is a link to the file from the Olympus camera.

Dropbox - 2018-04-02-190527-OlympusHomePhotos_DxO.jpg


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## Ysarex (Apr 12, 2019)

eja said:


> Ok, thanks for the reply.  Here is a link to the file from the Olympus camera.
> 
> Dropbox - 2018-04-02-190527-OlympusHomePhotos_DxO.jpg



That's the camera JPEG. Any chance you have a raw file. It would have an .orf extension.

Joe


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## eja (Apr 12, 2019)

Whoops.  My mistake.  Here is a link to the original .orf file.

Dropbox - 2018-04-02-190527-OlympusHomePhotos.ORF


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## Ysarex (Apr 12, 2019)

eja said:


> Whoops.  My mistake.  Here is a link to the original .orf file.
> 
> Dropbox - 2018-04-02-190527-OlympusHomePhotos.ORF



Got it -- I have to run out now for a couple hours and I'll get back to you later today.

Joe


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## Ysarex (Apr 12, 2019)

eja said:


> Whoops.  My mistake.  Here is a link to the original .orf file.
> 
> Dropbox - 2018-04-02-190527-OlympusHomePhotos.ORF



So first, yes -- no reason for the ISO 400 and that hurts.

You're not getting anything from the front flash fill attempt. So what you basically have is a backlit scene in which you're clipping the highlights nearly pointing into the sun and everything else is exposed less -- a lot less.

Here's a histogram of your raw file:






Your camera reaches clipping at a value of 4096. You can see where each graph basically stops at 4000 and just piles up into the clipping wall. If you follow back from there note how each graph has a small gap of nothing. The difference in your photo between the sky and foreground is such that there's literally an empty space between them.

The young man's face should have been bright enough to register somewhere between EV 1 and 2. I placed a circle on the graph marking the location of the tone data in his face. If we discount the sky for a minute as one photo and look at the histogram only considering the foreground data we have a multi stop underexposure at ISO 400.

Now the sky of course is there and you have part of it recorded. Your instinct was correct -- you can't shoot backlight like that without front fill. Assuming a willingness to still clip the sky your fill flash was at least 1.5 stops less than it needed to be; And there's your noise.

The photo can be noise filtered to pretty good effect. I used a product called NeatImage and ran your photo through.

Joe


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## eja (Apr 12, 2019)

Wow,  I feel like I've been to school and actually learned something. .  Thank you for the insights.  I'm also stunned at how well that noise reduction looks on that image.  So, I'm encouraged to try this again, working to get a better fill exposure and observe the results.  Maybe, I'll be pleasently surprised with how well a little point and shoot can work when it's given the proper chance.

I'll also have to check out rawdigger.  That was geat information that you interpreted from it for me.  Thanks again.


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## Derrel (Jun 13, 2019)

Recovering an underexposed Nikon D500 image - WildLight Photography


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## petrochemist (Jun 13, 2019)

PaulR70 said:


> I started this thread but I did not intend for it to become some long drama! I have been doing photography as a hobby off and on since 1968 and I understand some of differences between film and digital. I just understand that ISO can effect exposure in the digital camera period. Yes I am done with it!


Actually not the exposure but the brightness of the image.
The ideal exposure for an image will depend on the ISO (in film days at least there's a bit more variation possible today). I think it's high time a new term was coined that does include ISO, for the many situations where photographers use 'exposure' including the speed rating.


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## Ysarex (Jun 13, 2019)

petrochemist said:


> PaulR70 said:
> 
> 
> > I started this thread but I did not intend for it to become some long drama! I have been doing photography as a hobby off and on since 1968 and I understand some of differences between film and digital. I just understand that ISO can effect exposure in the digital camera period. Yes I am done with it!
> ...



I don't have an answer just an observation. Ilford struggled with the same problem long before digital came along so this is a very old problem. In their Manual of Photography which is arguably one of the more revered reference "bibles" out there they define exposure as expected -- measured in lux seconds as the total amount of light per unit area striking the film; a function of illuminance over time. In other words a function of  the two camera controls shutter speed and f/stop. They then go on to acknowledge that the common and casual usage of the term includes selecting film speed (ASA/DIN back then) and they devote some paragraphs to addressing what to do about that. Their solution for the sake of the text is to use the term "exposure" when they mean exposure and to use the term "camera exposure" as the alternate term when they mean setting the exposure in conjunction with selecting a film speed.

So it's a not a new problem for us. The confusion will continue and it's getting worse. I encountered this the other day:




Right there you have Nikon saying; *"Increasing ISO allows more light to be captured without adjusting aperture or shutter speed."* That's Nikon saying that and with a sexy Indian accent. WTF!

Joe


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