# Guide on ISO-speeds, suggestions anyone?



## kasperkjaerphoto (Jan 18, 2011)

Hi Photo Forum

I'm currently writting a guide on ISO-speeds for my blog, and I was wondering if anybody thinks anything is missing. Subjects covered:
 - Grainy images at high ISO-speeds.
 - High memory consumption at high ISO-speeds.
 - High battery consumption at high ISO-speeds.
 - Exposure time at different ISO-speeds.
 - Picture examples of what the different speeds do to the image.

I will post a link, when I am done writting the guide.
I am writting it because I think that the guides already online, are lacking in pictures comparing the different speeds and many beginner camera users are confused and thinks that shooting at ISO1600 all the time is the best, because it takes up the most space and space=quality.

Please comment and give advice.


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## Formatted (Jan 18, 2011)

> - High memory consumption at high ISO-speeds.
> - High battery consumption at high ISO-speeds.



Are these even true?


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## rufus5150 (Jan 18, 2011)

High-ISO images take more drive space (3200ISO images on my 7D are about 5meg more than ISO 100). 

The battery life one is interesting. In theory, I can see why that might be the case...


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## Josh66 (Jan 18, 2011)

Formatted said:


> > - High memory consumption at high ISO-speeds.
> > - High battery consumption at high ISO-speeds.
> 
> 
> Are these even true?


Yes.

My high ISO shots are noticeably larger than low ISO ones.  Take a look at the properties of your pictures...

The battery part, I don't know and have no way to test it...

I would think that it's true though, since the camera is doing more work, and you would think using more energy as a result.


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## AverageJoe (Jan 18, 2011)

So, a higher ISO value may give you a better exposure capturing more detail which in turn could mean a larger file size?  Is that the line of thinking?


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## Josh66 (Jan 18, 2011)

It's larger because more is being done to it.

It's amplified from the base ISO - that adds 'junk' to the file, which makes it bigger.


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## AverageJoe (Jan 18, 2011)

O|||||||O said:


> It's amplified from the base ISO - that adds 'junk' to the file, which makes it bigger.



"Junk" being noise/artifacts?


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## Josh66 (Jan 18, 2011)

AverageJoe said:


> O|||||||O said:
> 
> 
> > It's amplified from the base ISO - that adds 'junk' to the file, which makes it bigger.
> ...


Just extra data that isn't there for base ISO images.

High ISO on digital is just the base ISO, amplified.  When you do that, it's going to require more data...


'Junk' is just 'extra stuff'.  I'm not a programmer or engineer, so that's about as specific as I can get.


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## TheEugeneKam (Jan 18, 2011)

Well Electrical engeneering 101. The higher iso, the more the power consumption to an extent is true. The way digital camera's sensor gets higher sensetivity is by sending more power to the sensor. So there is the higher power consumption in theory. Sensors in cameras are analog, so the higher the power sent to the sensor the more distortion is created, hense the high ISO grain. So looking here at this the higher battery consumption makes sense. 
This however is very hard to prove fully and is absolutly situational. Therefore i would exclude this section. Now looking at this again in a different situation. comparing the high power consumption of 1600 ISO to 100 ISO, we see that the sensor has to operate (too lazy for math) for alot longer, and record the image for longer period of time, the camera processor has to compile more data, therefore it will use more power. 

This requires some math and a very good understanding of camera processor and the sensor, therefore it is not worth proving and is of no use as it will be different from camera to camera and  single result not always hold true generally, seeing as there are smaller sensors with high pixel desity and bigger sensors with the same megapixel count with less pixel density. Technically this is highly theoretical and useless information to almost every consumer, the only people that would care about this are the engeneers of the cameras. 
/end rant


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## PASM (Jan 18, 2011)

More gain .. more power. 



> The battery life one is interesting. In theory, I can see why that might be the case...


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## kasperkjaerphoto (Jan 19, 2011)

Seems like the guide is a good idea, many people obviously doesn't know that the high ISO-speed causes grain and large files.
The battery consumption is from personal experience, I have noticed that my battery drains a lot faster when I am photographing at higher speeds.
Thank you for your feedback everybody.


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## Overread (Jan 19, 2011)

Personally I would greatly underplay the filesize and battery consumption aspects of this guide. Almost add them as small trinkets of info rather than a mainstay in the differences of high ISOs. This is because the differences are both marginal and not important at the time of shooting to a photographer. 
They don't need to know that their camera is using a tiny bit more power or less power because so many other functions are doing the same thing all the time (eg viewing previews - menu controls etc..). So on that score they don't need to factor this as part of their shooting methodology.
Similarly whilst file size can be an important consideration for some the differences should be marginal to a photographer who would expect to have larger storage capacity for photos in their computer. Further you can't actively predict the values so it is again another concern that a photographer does not need to worry about when in the field and having to make the choice between high and low ISO.


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## kasperkjaerphoto (Jan 19, 2011)

Overread said:


> Personally I would greatly underplay the filesize and battery consumption aspects of this guide. Almost add them as small trinkets of info rather than a mainstay in the differences of high ISOs. This is because the differences are both marginal and not important at the time of shooting to a photographer.
> They don't need to know that their camera is using a tiny bit more power or less power because so many other functions are doing the same thing all the time (eg viewing previews - menu controls etc..). So on that score they don't need to factor this as part of their shooting methodology.
> Similarly whilst file size can be an important consideration for some the differences should be marginal to a photographer who would expect to have larger storage capacity for photos in their computer. Further you can't actively predict the values so it is again another concern that a photographer does not need to worry about when in the field and having to make the choice between high and low ISO.


 
My main focus point is on image quality, but an ISO1600 picture is nearly twice the size of an ISO100, so while it might not be important to the profesional photographer, to an amateur photographer it could mean not having enough room on the memory card.


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## Overread (Jan 19, 2011)

kasperkjaerphoto said:


> My main focus point is on image quality, but an ISO1600 picture is nearly twice the size of an ISO100, so while it might not be important to the profesional photographer, to an amateur photographer it could mean not having enough room on the memory card.



true but if they can't expose the shot correctly at ISO 100 surly that is going to introduce more noise data which bumps up the file size again.

Also I don't know about other cameras, but when it comes to file space most only display a rough guildline as to the number of photos as person can take - actual file storage space used is only shown (on mine) when you go to the formate memory card menu option (not something you want to be hovering over just after taking a whole cards worth of shots ). I just feel you're going for a level of detail which is factually accurate, but which in practice is not something that is practical for the photographer to be concerned about


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## kasperkjaerphoto (Jan 19, 2011)

Overread said:


> kasperkjaerphoto said:
> 
> 
> > My main focus point is on image quality, but an ISO1600 picture is nearly twice the size of an ISO100, so while it might not be important to the profesional photographer, to an amateur photographer it could mean not having enough room on the memory card.
> ...



There is less noise at ISO100, the only downside is the longer exposure time, this does not take up space, but it increases the risk of camera shake.

I am not talking about the estimated space, I'm talking about the actual file size, in my tests an average increase of 90% is to be expected when going from ISO100 to ISO1600 when taking photos in an enviroment where ISO200 or ISO400 would be recommended.


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## Drake (Jan 19, 2011)

That's right, shots ISO 100-200 from my 10MP Rebel XS are about 8-9mb (RAW). Take the ISO to 1600, and the output is about 10-11, sometimes even 12mb.

But I think you are missing the dynamic range loss. Depending on the camera, jpeg/raw and the testing procedure the results might be different, but just to give you an idea - a page from the test of a Rebel XS, by a very reputable Polish site.

Test Canon EOS 1000D - Zakres tonalny - Test aparatu - Optyczne.pl

I don't expect you to read the text, but just look at the chart

The black dots stand for the total DR.
Green dots - good quality
Red dots - very high quality

As you can see, the 'good quality' DR may shrink from 6EV to 3EV, which is a lot. 

Sorry for the link in Polish, couldn't find one fast enough in English.


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## kasperkjaerphoto (Jan 19, 2011)

Drake said:


> That's right, shots ISO 100-200 from my 10MP Rebel XS are about 8-9mb (RAW). Take the ISO to 1600, and the output is about 10-11, sometimes even 12mb.
> 
> But I think you are missing the dynamic range loss. Depending on the camera, jpeg/raw and the testing procedure the results might be different, but just to give you an idea - a page from the test of a Rebel XS, by a very reputable Polish site.
> 
> ...



I don't think I'm pro enough to quite understand what you mean, but as far as I can interpret you are agreeing with me that high ISO-speeds give low quality images (if an image can be achieved without blur at low ISO-speeds).


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## kasperkjaerphoto (Jan 19, 2011)

@erose86:
I am not trying to discourage it at all costs, but a friend of mine says that she always shots at ISO1600 because she thinks it gives better images (the forementioned reasons) it is this common misconception I am trying to get rid of.
I am aware that I sound against high ISO-speeds, that is because as a general rule I avoid them, unless I have problems with camera shake, then I have no choice.
But I think everyone would agree that if you can snap a photo without blur at ISO100, you wouldn't choose ISO400 or higher?


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## Drake (Jan 19, 2011)

kasperkjaerphoto said:


> Drake said:
> 
> 
> > That's right, shots ISO 100-200 from my 10MP Rebel XS are about 8-9mb (RAW). Take the ISO to 1600, and the output is about 10-11, sometimes even 12mb.
> ...


I am no pro either, but from what I understand it's more or less that when you shoot the camera (Rebel XS in this case) at ISO 100, you get about 6 stops of good quality image, and about 1,5 stop in addition of the things you can recover - highlights (at the price of some weird colors, posterization, color clipping, you name it) and shadows (at the price of some heavy noise). That adds up to a total of about 7.5 EV total dynamic range.

At ISO 1600 you get only about 3 stops of the high quality image. The total dynamic range is similar, about 7,5 stops, but you have to recover the remaining lower quality 4 stops first.



kasperkjaerphoto said:


> But I think everyone would agree that if you can snap a photo without blur at ISO100, you wouldn't choose ISO400 or higher?


No doubt about that, but sometimes when you don't have time to check the LCD and you want to be 100% positive you got it right because you won't have the opportunity to get a second try, you might want to set the ISO a little bit higher, just to be sure.


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## kasperkjaerphoto (Jan 19, 2011)

erose86 said:


> kasperkjaerphoto said:
> 
> 
> > But I think everyone would agree that if you can snap a photo without blur at ISO100, you wouldn't choose ISO400 or higher?
> ...



I think I will write at the end that it is a trial-and-error thing, and when in doubt and snapping a really important photo that you can't do over, use automatic ISO, untill you have mastered manual ISO.


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## Garbz (Jan 20, 2011)

TheEugeneKam said:


> Well Electrical engeneering 101. The higher iso, the more the power consumption to an extent is true. The way digital camera's sensor gets higher sensetivity is by sending more power to the sensor.



That's not entirely true. A typical CCD / CMOS sensor effectively reacts like a reverse biased PN junction. ... Actually they are a variant of a reverse biased PN junction. The bias part causes a small base current to flow through the junction, this exists regardless of light hitting it and is called the dark current. Now what is true that for changes in amplification scheme (resistive load across the sensor) the dark current changes. However this does not change the sensitivity much at all. The majority of this is done at the amplifier and analogue to digital converter. 

Now the other power consumption of any type of photo cell requires a photon with energy greater than the bandgap energy to excite the depletion region and create an electron-hole pair allowing electrons to flow through the device.

Errr now in english: Light hit sensor, bit of current moves forward.

For two pictures of the same brightness this current is equal if the amplification on the other end is the same, but it's not. In fact if you amplify a weaker signal the sensor can actually use LESS power since there's less electrons to flow, and the sensor isn't energised for as long reducing the dark current power demands.

To judge the power consumption you need to consider how does the power consumption of the sensor being on for less time, at a different bias level (affecting the bandgap energy slightly too which is where the other truth from your statement that a sensor can be more sensitive), compare to the increased demands on the amplifier, and analogue to digital converter (and if you shoot JPEG, the additional delay due to noise reduction processing which can be significant if you're squeezing every last drop of power out of a microprocessor).

I think in truth this not only depends on each camera design, but also how each picture is taken.  

That's my take on the theory, in practice I haven't seen a difference when shooting night shots at ISO100 vs ISO800. My camera chews a battery in roughly an hour regardless of how I set up the shot. 




AverageJoe said:


> So, a higher ISO value may give you a better exposure capturing more detail which in turn could mean a larger file size?  Is that the line of thinking?



All things being equal the compressibility of an image depends on how well the detail reacts to the algorithm. High-ISO images aren't magically larger, take a low-ISO shot of a noise source and you'll have just as large (infact larger since high-ISO NR probably won't be applied) images. 

The size of an image is exclusively determined by the content. High-ISO adds noise. The difference in size between a high ISO and low ISO image of a blue sky will be quite big. The difference in noise between a high ISO and low ISO image of something with a complicated fine and contrasty texture that is in perfect focus will be non-existent.


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## kasperkjaerphoto (Jan 20, 2011)

Thank you for all the responses, I have finished my article and posted it on my blog.

Kasper Kjær Photography: ISO-speeds: What is the difference?


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