someone point me the way to selecting ISO

This is based on my experiance with the 50D. It isn't based on rigerous techincal studies and may in fact be wrong.

I don't notice any difference between ISO 100 and 200. So I very seldom set to ISO 100 even in bright sunlight. I happily shoot with shutter speeds faster than 1/1000 of a second with my 17-50 f2.8 lens at ISO 200 even though I could happily shoot at ISO 100 with a plenty fast shutter speed.

The difference between 200 and 400 is not very noticable. When printing at sizes 8*10 and smaller it is even less noticable. Please remember that if you are exporting to web sizes (600*900 px for me) or printing then what you see as noise at the pixel level won't directly translate to noise in the finished product (there may be noise in that product but you won't be seeing the pixel level noise).

The 1/3rd stop ISOs seem to have slightly more noise to me. I could be wrong but it seems that ISO 320 has more noise than ISO 400. ISO 640 seems to have as much noise as ISO 800 to me. So below ISO 800 I very seldom use 1/3rd stop ISOs.

Above ISO 800 I will use 1/3rd stops instead of choising ISO 1600, but I haven't done enough low light shooting to say it gives you better noise control. This in fact may very well be a bad idea.

Now about choising higher ISOs. If you choose a lower ISO and have to compensate for even a slight underexposuere in post you will generally end up with more noise in the finished image than if you chose a higher ISO. That is to say if you choose ISO 800 to keep noise low and get underexposure that you fix in post you will probably end up with more noise than if you chose 1600 and didn't have to brighten it up in post. (this may be what Daniel was saying, but I am not sure).

I only use ISOs over 1600 when I have to get the shot. H1 and H2 are generally novelites as far as I am concerned. They make bigger files with very very visable noise.

Hope this helps.

Let me explain it in different words:

Here is how most people understand high ISO:

• When I use autoexposure mode.
  
• At low ISO, the noise is very little.
  
• At high ISO, the noise is very high.
  
• Therefore, high ISO causes noise (incorrect).

• When I reduce exposure, it causes more noise.
  
• Sometimes when I reduce exposure, I am left with more highlight headroom than I need.
  
• In those cases, I can trade away the highlight headroom to get less noise by using high ISO.
  
• This is all thanks to the fact that the 50D sensor technology has an advanced feature where the actual read noise is reduced at high ISO. Some other cameras, such as MFDB, don't perform that way.

MarKap77 wrote in post #8362249
Your advice is completely contrary to everything I have ever learned about ISO and exposures. Care to give a reference to some book or manual or something to back up your statements?

Just take two pictures with the same exposure (i.e. same f-number and shutter). Set one to ISO 100 and the other to ISO 1600. Then examine the shadows of both images and tell me which one has more noise. (Of course there is a difference in blown highlights, which is why I explained "ETTR then ITTR".)

MarKap77 wrote in post #8362249
I also found several factual errors in your post. For instance, the Canon 50D has 1/3 stop increments of ISO.

When I said "not 1/3-stop", I was not saying that the 50D does not have 1/3 stop increments of ISO. I was saying "this post applies to the full-stop-increment ISO settings. Things are slightly different for the 1/3-stop ISO settings, and therefore this post does not apply to them."

MarKap77 wrote in post #8362249
Lastly, my practical experience tells me that your assertion that 1600 ISO has the lowest noise is incorrect. Any image I have ever taken with any digital camera, as you increase the ISO, you increase the noise.

No. Try the above experiment and you'll find that is incorrect. *Decreasing exposure* causes an increase in noise. And people tend to use high ISO at the same time as they decrease exposure, but that doesn't mean the ISO caused the noise. If it did, then keeping the exposure the same and increasing ISO would increase noise. It doesn't. It decreases noise (and blows highlights).

This is one case where the wide use of autoexposure causes many folks to look at things incorrectly.

Saying "high ISO causes noise" is similar to saying "high ISO causes thin DOF". Everyone knows that's not correct. High ISO *tends* to be used with wide f-numbers, and wide f-numbers tend to result in thinner DOF, but that doesn't mean the thin DOF was caused by ISO. In the same way, noise is not caused by ISO, it is caused by underexposure.

stsva wrote in post #8362430
I'm with MarKap77 re: Daniel Browning's post. I think many photographers would agree that, for any given ISO, exposing to the right will result in lower noise for that ISO setting compared to using an "average" exposure or underexposing.

Of course. That's precisely what I said. See the paragraph starting with "ETTR". Also note how I said to "ETTR then ITTR." That means to expose to the right and only then increase ISO (if possible without blowing important highlights).

stsva wrote in post #8362430
I don't think many would agree that increasing the ISO (say using ISO 400) combined with exposing to the right will result in lower noise compared to using a lower ISO setting (say ISO 200) combined with exposing to the right.

You have it backwards. What you're describing is "ITTR then ETTR", which is the opposite of what I said in my post.

Jared Byer wrote in post #8362543
I don't notice any difference between ISO 100 and 200.

Agreed.

Jared Byer wrote in post #8362543
Now about choising higher ISOs. If you choose a lower ISO and have to compensate for even a slight underexposuere in post you will generally end up with more noise in the finished image than if you chose a higher ISO. That is to say if you choose ISO 800 to keep noise low and get underexposure that you fix in post you will probably end up with more noise than if you chose 1600 and didn't have to brighten it up in post. (this may be what Daniel was saying, but I am not sure).

Essentially, yes. Most people have their own home-grown and incorrect explanations why low ISO has more noise than high ISO when exposure is fixed. The real reason is that the sensor has physically lower read noise at higher ISO.

Of course, ideally, we would like low ISO to have the same low read noise that high ISO has. If it did, there would never (ever!) be any reason to use high ISO. A digital push of low ISO would give you the exact same image as a high ISO shot, but it would have many more stops of highlight headroom (more dynamic range).

In fact, some cameras are like that, including most MFDB. That is why understanding how high ISO *reduces* noise is important.

One reltively easy way to learn the relationship bewtween ISO, shutter speed and aperture is to shoot in Manual mode. This is how I learned way back in the 60s when autoexposure was not a feature on my cameras.

Do it when you are not trying to get 'keeper' shots. Go take a picture of the fence, of the dog, of a car. Shots that you delete right after taking. Fiddle with these three controls and see what it does to your pictures and how they affect each other.

I feel I have a solid understanding of all three and I would have never gotten from shooting in auto.

p.s. while taking the time to write a tome is admirable, I don't think the OP is ready for the highly technical side of sensor response and the like ...

Daniel Browning wrote in post #8363118
Saying "high ISO causes noise" is similar to saying "high ISO causes thin DOF". Everyone knows that's not correct. High ISO *tends* to be used with wide f-numbers, and wide f-numbers tend to result in thinner DOF, but that doesn't mean the thin DOF was caused by ISO. In the same way, noise is not caused by ISO, it is caused by underexposure.

no. what you're saying is misleading because people can be led to believe that higher ISO has no consequence, when in fact it does.

HIGH ISO WILL CREATE MORE NOISE.

the proof is easy to demonstrate. take two frames with the same exposure. let's say:

- 1/25s f/2.8 ISO200

and

- 1/25s f/8 ISO1600

if the exposure is the same, the higher ISO frame will have more noise. if this wasn't true, there would be NO benefit to shooting at lower ISOs. we'd just always try to expose properly and max out shutter speeds for most images.

IMHO Daniel has a good point, but his wording of it, especially in the first post, was poorly chosen. Likely trying to get more discussion.

I'm going to put it another way, not necessarily exactly as Daniel meant, but ...

1. Boosting ISO can increase noise.
2. Underexposing an image can create MORE noise then pushing ISO.
3. Underexposing an image in a high ISO setting will create lots of noise.

4. Conclusion: Therefore it is better to push ISO high enough to prevent underexposure, to ETTR, than it is to shoot with the next lowest ISO settings which may create under exposure noise, and thus even MORE noise.

Now there are problems with this theory;

1. We have also had long debates over whether it is true or not if shooting underexposed actually adds more noise,...
(IMHO it certainly does. ) Which brings us to the whole subject of exposing "to the right" or ETTR as a debate in itself.

2. When you need every ounce of shutter speed to stop motion, regardless of what your cameras ISO settings can be, we sometimes MUST under expose in RAW and push, just to get a working shutter speed. that's exposing to the left!

3. Wait till Pixmantra gets in here and starts talking about the MkIII and it's "hidden" high ISO performance! I think he and Daniel might come to blows!

From Daniel Browning's latest post:
This is all thanks to the fact that the 50D sensor technology has an advanced feature where the actual read noise is reduced at high ISO. Some other cameras, such as MFDB, don't perform that way.

Are you saying that, all other things being equal, a 50D will have lower absolute (not relative) noise levels at a higher ISO than a lower ISO?

I've been reading and want to thank all for chiming in. This has touched on several topics that people coming here encounter early on.

CyberDyneSystems wrote in post #8363240
IMHO Daniel has a good point, but his wording of it, especially in the first post, was poorly chosen. Likely trying to get more discussion.

I'm going to put it another way, not necessarily exactly as Daniel meant, but ...

1. Boosting ISO can increase noise.
2. Underexposing an image can create MORE noise then pushing ISO.
3. Underexposing an image in a high ISO setting will create lots of noise.

4. Conclusion: Therefore it is better to push ISO high enough to prevent underexposure, to ETTR, than it is to shoot with the next lowest ISO settings which may create under exposure noise, and thus even MORE noise.

Now there are problems with this theory;

1. We have also had long debates over whether it is true or not if shooting underexposed actually adds more noise,...
(IMHO it certainly does. ) Which brings us to the whole subject of exposing "to the right" or ETTR as a debate in itself.

2. When you need every ounce of shutter speed to stop motion, regardless of what your cameras ISO settings can be, we sometimes MUST under expose in RAW and push, just to get a working shutter speed. that's exposing to the left!

3. Wait till Pixmantra gets in here and starts talking about the MkIII and it's "hidden" high ISO performance! I think he and Daniel might come to blows!

this makes sense, but claiming that high ISO has no direct effect on noise is just plain misleading.

Thanks for clearing things up, CDS! I was going to report this one as I was confused myself and I work with ISO all over the place for many venues and still can't explain it for anyone to understand how I adjust my 5DII.

Depending on the camera model you have, ISO settings are not the same output from my 40D to my 5DII. I can shoot at ISO 3200 on my 5DII and get no noise at all, if I adjust the aperture and shutter speed correctly. My 40D doesn't even go to 3200 unless I set it in Custom settings. Learn the model you own, talk to the people who work with that model and adjust the 3 elements to proper exposure and you're good. I don't underexpose because I don't like noise, and as it is debated here, I choose not to underexpose and then hope the noise is at a minimum. I try to correctly expose from the start and not worry about it later. Just practice, and don't be nervous to shoot in manual and play with all the settings. It's the only way you will improve and get the gear to work for you.

alt4852 wrote in post #8363207
no. what you're saying is misleading because people can be led to believe that higher ISO has no consequence, when in fact it does.

No. I think people are perfectly capable of understanding the truth about what causes noise.

alt4852 wrote in post #8363207
HIGH ISO WILL CREATE MORE NOISE.

No, underexposure will create more noise.

alt4852 wrote in post #8363207
the proof is easy to demonstrate. take two frames with the same exposure. let's say:

- 1/25s f/2.8 ISO200

and

- 1/25s f/8 ISO1600

Those are most definitely *not* the same exposure. They only have the same brightness ("apparent" exposure).

I think we may have stumbled on the reason why so many people are getting confused. When I used the term "exposure", I was referring to the real and correct definition of the word. Unfortunately, most POTN members are not aware of the difference. Therefore, I need a new word to take the place of "the concept formerly known as exposure".

Any suggestions? How about "light intensity", meaning "the intensity of light falling on the sensor". I think that's similar enough to the true definition of "exposure", so I'm going to go with that until I hear a better suggestion.

FWIW, I think using made up terms like "light intensity" is a *lot* more confusing that just learning and teaching the correct terms, but I'm willing to adapt if you guys don't want to start using the correct terms.

[EDIT: "light intensity" is a very poor synonym for exposure because it only works when shutter speed is kept the same. Sorry for suggesting it. I should have gone with "total light per area".]


To be clear, here are the definitions:

• Exposure (true definition): Intensity of light falling on the sensor. [EDIT: correction: total light per area falling on the sensor.]
  
• Exposure (as misunderstood by most photographers): Brightness of the image on the LCD.
  
• Light intensity: Made up term as an alias for the true definition of "exposure", since too few people know the true definition.

alt4852 wrote in post #8363207
if the exposure is the same, the higher ISO frame will have more noise.

If brightness is the same, the higher ISO frame will have more noise, that is correct. If you go back and re-read the post and transpose "Exposure" with its true definition ([EDIT:"total light per area"]), you will see that what I said is correct: when the light intensity is the same, the higher ISO frame will have *less* noise.

What you showed is that a lower light intensity causes more noise (f/8 is a lower intensity than f/2.8 )

CyberDyneSystems wrote in post #8363240
IMHO Daniel has a good point, but his wording of it, especially in the first post, was poorly chosen.

Aside from using the word exposure correctly, which caused a lot of confusion, I think I did OK. Next time I will use "light intensity" and include a footnote explaining why I'm avoiding the word "exposure".

I really did try to make an effort to show the difference between the "normal" paradigm and the correct paradigm.

I think the reason it's hard to understand is because it's a huge paradigm shift. It's hard to accept that the way you understood things for all these years is fundamentally backwards. (It was for me when I first found out that high ISO reduced noise.)

CyberDyneSystems wrote in post #8363240
Likely trying to get more discussion.

Not at all, I promise. I'm trying to put it as clearly as I can.

CyberDyneSystems wrote in post #8363240
I'm going to put it another way, not necessarily exactly as Daniel meant, but ...

1. Boosting ISO can increase noise.

That is demonstrably false. Compare:

* 1/125 f/2.8 ISO 100
* 1/125 f/2.8 ISO 1600

The ISO 1600 has much less noise. Of course it has four stops of blown highlights compared to the ISO 100 shot, and that's why no one would shoot ISO 1600 unless they were willing to trade four stops of highlight headroom.

CyberDyneSystems wrote in post #8363240
4. Conclusion: Therefore it is better to push ISO high enough to prevent underexposure,

OK, here what you mean is "it is better to push ISO high enough to prevent a dark image". That's correct. It's the essense of "ITTR": ISO To The Right.

CyberDyneSystems wrote in post #8363240
than to shoot with the next lowest ISO settings which may create under exposure noise, and thus even MORE noise.

You mean "brightness" instead of exposure. If we make that correction:

CyberDyneSystems wrote in post #8363240
than to shoot with the next lowest ISO settings which may create [dark image] noise, and thus even MORE noise.

That's correct. Here is another way to do it:

Using one stop lower ISO setting will result in an image that is 1 stop darker. Noise will only be *slightly* more.
Using one stop lower light intensity will result in image that is 1 stop darker. Noise will be *much* more.

CyberDyneSystems wrote in post #8363240
Now the funny part is we have also had long debates over whether it is true or not if shooting underexposed actually adds more noise,...

For Canon cameras from ISO 100 to 1600, it's a fact. The only thing one can say is that if the image is not brightened in post, one will not *see* the increase in noise (it's still there, though).

stsva wrote in post #8363275
Are you saying that, all other things being equal, a 50D will have lower absolute (not relative) noise levels at a higher ISO than a lower ISO?

In photo-electron-equivalents, read noise at ISO 100 is 13.8 electrons, but only 2.6 electrons at ISO 1600.

You are however over simplifying IMHO;

Daniel Browning wrote in post #8363118
....

Here is how most people understand high ISO:

• When I use autoexposure mode.
  
• At low ISO, the noise is very little.
  
• At high ISO, the noise is very high.
  
• Therefore, high ISO causes noise (incorrect).

The logical error is that correlation is not causation. In autoexposure mode, high ISO reduces the exposure. It is the reduced exposure that causes the noise to be very high. Not the high ISO. .....

Underexposure is bad, maybe worse, but it is not the only reason that noise is created when we boost ISO settings, the act of boosting the ISO alone with identical exposure settings will increase the measurable noise.

Again, I see your point, but to me you are excluding information, in fact typing information contrary to the truth to make your point.

Yeah this whole "fact" thing ...
I don't buy it at all.

You can say fact all you want, but I don't see it in practice.

IF the "fact" is that a totally blown out image with little usable data has less noise...
Well that's not of use to anyone as in practice that image is far less useful than one with a little noise.

It's got to work for us when were taking photos.. not when were in a lab shooting 255 white.

when I say "same exposure" yes, semantically you can call me, as I mean with same = meter setting.
If one is 4 stops blown that is not what I mean by same exposure,. I'm referring to keeping the exposure = re: metering taking the boosted ISO into account.

Daniel Browning wrote in post #8363536
No. I think people are perfectly capable of understanding the truth about what causes noise.

Those are most definitely *not* the same exposure. They only have the same brightness ("apparent" exposure).

I think we may have stumbled on the reason why so many people are getting confused. When I used the term "exposure", I was referring to the real and correct definition of the word. Unfortunately, most POTN members are not aware of the difference. Therefore, I need a new word to take the place of "the concept formerly known as exposure".

Any suggestions? How about "light intensity", meaning "the intensity of light falling on the sensor". I think that's similar enough to the true definition of "exposure", so I'm going to go with that until I hear a better suggestion.

FWIW, I think using made up terms like "light intensity" is a *lot* more confusing that just learning and teaching the correct terms, but I'm willing to adapt if you guys don't want to start using the correct terms.

To be clear, here are the definitions:

• Exposure (true definition): Intensity of light falling on the sensor.
  
• Exposure (as misunderstood by most photographers): Brightness of the image on the LCD.
  
• Light intensity: Made up term as an alias for the true definition of "exposure", since too few people know the true definition.

If brightness is the same, the higher ISO frame will have more noise, that is correct. If you go back and re-read the post and transpose "Exposure" with its true definition ("light intensity"), you will see that what I said is correct: when the light intensity is the same, the higher ISO frame will have *less* noise.

What you showed is that a lower light intensity causes more noise (f/8 is a lower light intensity than f/2.8 )

Aside from using the word exposure correctly, which caused a lot of confusion, I think I did OK. Next time I will use "light intensity" and include a footnote explaining why I'm avoiding the word "exposure".

I really did try to make an effort to show the difference between the "normal" paradigm and the correct paradigm.

I think the reason it's hard to understand is because it's a huge paradigm shift. It's hard to accept that the way you understood things for all these years is fundamentally backwards. (It was for me when I first found out that high ISO reduced noise.)

ex⋅po⋅sure
  /ɪkˈspoʊʒər/ [Ik-spoh-zher]

–noun

a. the act of presenting a photosensitive surface to rays of light.
b. the total amount of light received by a photosensitive surface or an area of such a surface, expressed as the product of the degree of illumination and the period of illumination.
c. the image resulting from the effects of light rays on a photosensitive surface.

i hate to break out the dictionary, but that's as plain as it gets. the most scientifically correct definition of an exposure refers to the total amount of light, which includes duration or period of illumination. intensity is intensity.

you could argue that my usage of it by referring to the resulting image is false since technically the sensitivity of the medium the exposure is collected on does not technically qualify as being part of the collective term of "exposure", but the last line clearly shows how using the term in this manner is acceptable. are you sure you're not just trying to refit the word into what YOU perceive it to be?

Daniel Browning wrote in post #8363536
That is demonstrably false. Compare:

* 1/125 f/2.8 ISO 100
* 1/125 f/2.8 ISO 1600

The ISO 1600 has much less noise. Of course it has four stops of blown highlights compared to the ISO 100 shot, and that's why no one would shoot ISO 1600 unless they were willing to trade four stops of highlight headroom.

You mean "brightness" instead of exposure.

In photo-electron-equivalents, read noise at ISO 100 is 13.8 electrons, but only 2.6 electrons at ISO 1600.

..are you serious? in a properly exposed photo, a higher ISO will garner higher visible noise. nobody cares about a theoretical frame where you're overexposed three stops of light to prove that ISO1600 renders less noise per electron than a well-exposed ISO200 shot.

CyberDyneSystems wrote in post #8363572
Yeah this whole "fact" thing ...
I don't buy it at all.

You can say fact all you want, but I don't see it in practice.

IF the "fact" is that a totally blown out image with little usable data has less noise...
Well that's not of use to anyone as in practice that image is far less useful than one with a little noise.

It's got to work for us when were taking photos.. not when were in a lab shooting 255 white.

when I say "same exposure" yes, semantically you can call me, as I mean with same = meter setting.
If one is 4 stops blown that is not what I mean by same exposure,. I'm referring to keeping the exposure = re: metering taking the boosted ISO into account.

precisely.

My understanding is that digital sensors have a native level of light sensitivity that corresponds to an ISO. I believe most canon DSLRs are enginered so that ISO 100 is the native light sensitivity of the sensor. Higher ISO's increase light sensitivity by amplifing the electrical signal received from the sensor. The noise gets amplified also. However when high ISO's are traditionally used, low light, there is less signal to the same amount of noise. Both the signal and noise get amplified but because there is less signal the noise appears to be greater.

There are different ways to compare ISO's and noise.

Setup 1:
There is the same amount of ambient light on the photo subject.
Shot 1: ISO=100, Shutter=1/60th, f/2.8
Shot 2: ISO=800, Shutter=1/1000th, f/2.8
In this setup the second shot will have more noise.

Setup 2:
There is the same amount of ambient light on the photo subject.
Shot 1: ISO=100, Shutter=1/60th, f/2.8
Shot 2: ISO=800, Shutter=1/60th, f/11
In this setup the second shot will have more noise.

Setup 3:
The first shot has 4-stops more light on the photo subject than the second has.
Shot 1: ISO=100, Shutter=1/60th, f/2.8
Shot 2: ISO=800, Shutter=1/60th, f/2.8
In this setup the second shot will have more noise.

Setup 4:
There is the same amount of ambient light on the photo subject.
Shot 1: ISO=100, Shutter=1/60th, f/2.8
Shot 2: ISO=800, Shutter=1/60th, f/2.8
In this setup one of the images will either be underexposed or overexposed or both will not have the same exposure.

I point this all out to say that higher ISOs do have more noise If you have proper exposure on both images.

On this again,
Now who is it that is drawing conclusions re: cause and effect?
Again, even if the fact is that the totally blown out image has less noise left to its total loss of image information, ...

If your theory is based on images blown out by four stops, how do you draw the conclusion that the lower measurable noise is due to the electronics/mechanics of higher iso setting?

You can't.

The cause of lower noise could be ( likely is IMHO) the loss of image data. Color/detail lost to the nether regions of pure white = noise lost too, not unlike losing details when we run noise filters.

Blowing a huge percentage of the image is the heavy handed noise filter taken to it's extreme, leaving us again with an unusable image.