Choosing ISO basics

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yoshimi

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I'm still learning so please bear with me - I tend to shoot in Av for static shots and Tv for moving object and always leave ISO set to auto.

I'm interested i understanding the effects of using manual ISO. Where do I start, can anyone give me a few examples of what they consider and what values they use when setting ISO? Also, how would you work i.e. set ISO first then set aperture and shutter speed - I'm just very confused.

Thanks
 
On Av mode, only increase the ISO in occasion that the shutter speed calculated by the camera isn't fast enough for your subject at the aperture you selected. Use the lowest base value every other time unless you love noisy pictures.

My hands are quite shaky so I try to keep the shutter speed above 1/60s for normal shots and 1/500s for fast moving subjects like during a sports shoot.

e.g. Set the aperture first to get the desired depth of field effect.
1) Your dog won't stay still indoors, you bump up the ISO to 800 or 1600 to get a sharp pictures.
2) Later on you go outdoors and the sun is shining brightly, bring ISO down to 100 or 200, depending on the model of your camera.
 
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To minimise the potential for noise in the image use the lowest ISO that gives a workable shutter speed for your chosen aperture (in Av mode, for Tv that gives a workable aperture for your chosen shutter speed). You might make a guess at that and then find yourself having to adjust once you've taken a meter reading or fires off a test shot.

What is "workable" will depend whether you're hand-holding or using a tripod/rest (for a workable shutter speed) or the depth of field you need (for a workable aperture).

Not all DSLRs will use the full range of available ISO settings in automatic mode (this varies between manufaturers and models).
 
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It's pretty straightforward really - as Alastair said you want to set the lowest ISO you can get (which gives the least image noise) which enables you to use a fast enough shutter speed and/or a suitable aperture for the subject you're shooting. So in practice set an ISO, check your shutter speed and aperture, and if not suitable, increase the ISO until they are.

I never use auto ISO and it wouldn't bother me if my cameras didn't have a TV mode at all - I invariably shoot in AV mode or sometimes in Manual mode.
 
Raising ISO does not increase noise. Capturing fewer photons does. ISO does not affect how many photons are captured. That's down to how much light there is and your chosen aperture and shutter speed.

In fact, for any given number of photons captured raising the ISO will reduce noise. In other words it is better to shoot a correct exposure at 1600 ISO than to shoot at 800 ISO and underexpose by 1 stop or to shoot at 400 ISO and underexpose by 2 stops and so on.

Here's an example from a sequence I shot a few minutes ago. I metered off the grass and it read 0 on the meter at 400 ISO. Without adjusting shutter speed or aperture (the controls which affect how much light is recorded) I took several shots simply varying ISO from each one to the next. So at 100 ISO the grass was 2 stops under. At 200 ISO at was at 1 stop under, and so on up till 3 stops over at 3200 ISO.

Here is a comparison of the 100 ISO shot with the 3200 ISO shot. I've used auto tone in Lightroom to equalise (more or less) the appearance of the shot. To my eyes the version shot at 3200 ISO is actually cleaner, and definitely with less banding, than the shot that was underexposed at 100 ISO. This does not come as a surprise to me.

(Click the size bar for a proper look.)

20110130_154135_000.jpg


It's not high ISO that is the problem. It's underexposure. Raising the ISO actually helps a little.

Put another way, select the shutter speed and aperture you want and then choose the highest ISO you can that will not result in clipping of important highlights. That said, there are some ISO values that should be avoided on some cameras so pick your ISO wisely. However, do not think that keeping it artificially low will reduce noise. If doing so results in an underexposed image then you'll be worse off.

High ISO gets a bad name for noise because people combine it with fast shutter speeds and low light - they don't capture enough photons. It's not the ISO choice that is the problem. It's failure to saturate the sensor. In those situations high ISO is your friend. Don't be afraid to use it.

By the way, all this is related to the good practice of ETTR (expose to the right). If you're already against the wall on shutter speed, aperture and available (or supplementary) light then the only thing left to increase in order to ETTR is your ISO. Do it.
 
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Wow - theres a lot to take in for a beginner but thank you for all your considered replies.

So am I right in thinking that its underexposure that creates noise when underexposure is caused by low light where the only way to get over unusably slow shutter speeds is to increase the sensitivity of the sensor?
 
Yeah, sorry, that probably was a bit heavy going for a "beginner", but basically you've got it. Use whatever ISO you need to get a good exposure in camera rather than trying to brighten an underexposed image later on.
 
Yoshimi - I work to the train of thought that it's always best to have enough exposure leeway by having a higher base ISO, than come to a point when you've run out of options because you've kept ISO low and can't get a fast enough shutter speed. The only time I know ISO 100 will be fine is A) i the studio where light is controlled, and B) those mega-sunny days when you're getting super fast shutter seeds at f/8 etc. The rest of the time I shoot ISO 200 or 400 to give me enough room to change exposure values. Stuff noise; it's better to have a noisey shot than one that's got camera shake....
 
Alastair said:
To minimise the potential for noise in the image use the lowest ISO that gives a workable shutter speed for your chosen aperture
Click to expand...

tdodd said:
High ISO gets a bad name for noise because people combine it with fast shutter speeds and low light - they don't capture enough photons. It's not the ISO choice that is the problem. It's failure to saturate the sensor. In those situations high ISO is your friend. Don't be afraid to use it.

By the way, all this is related to the good practice of ETTR (expose to the right). If you're already against the wall on shutter speed, aperture and available (or supplementary) light then the only thing left to increase in order to ETTR is your ISO. Do it.
Click to expand...

Surely we're saying (almost) the same thing?

Underexposure is not good.. but ISO is very rarely going to be the first thing you think about upping to correct it.

And if I could correctly expose the same scene at ISO100 and ISO800 and ISO3200, will I not have more noise at the higher ISO levels? Yes, it results from the increased sensitivity requiring the capture of less photons. But the direct choice that resulted in the higher noise levels was the choice to use a higher ISO. Therefore, to all practical intents and purposes.. having the ISO higher than you need will result in am image being noisier than it need be.
 
tdodd said:
Raising ISO does not increase noise. Capturing fewer photons does. ISO does not affect how many photons are captured. That's down to how much light there is and your chosen aperture and shutter speed.

In fact, for any given number of photons captured raising the ISO will reduce noise. In other words it is better to shoot a correct exposure at 1600 ISO than to shoot at 800 ISO and underexpose by 1 stop or to shoot at 400 ISO and underexpose by 2 stops and so on.

Here's an example from a sequence I shot a few minutes ago. I metered off the grass and it read 0 on the meter at 400 ISO. Without adjusting shutter speed or aperture (the controls which affect how much light is recorded) I took several shots simply varying ISO from each one to the next. So at 100 ISO the grass was 2 stops under. At 200 ISO at was at 1 stop under, and so on up till 3 stops over at 3200 ISO.

Here is a comparison of the 100 ISO shot with the 3200 ISO shot. I've used auto tone in Lightroom to equalise (more or less) the appearance of the shot. To my eyes the version shot at 3200 ISO is actually cleaner, and definitely with less banding, than the shot that was underexposed at 100 ISO. This does not come as a surprise to me.

(Click the size bar for a proper look.)

20110130_154135_000.jpg


It's not high ISO that is the problem. It's underexposure. Raising the ISO actually helps a little.

Put another way, select the shutter speed and aperture you want and then choose the highest ISO you can that will not result in clipping of important highlights. That said, there are some ISO values that should be avoided on some cameras so pick your ISO wisely. However, do not think that keeping it artificially low will reduce noise. If doing so results in an underexposed image then you'll be worse off.

High ISO gets a bad name for noise because people combine it with fast shutter speeds and low light - they don't capture enough photons. It's not the ISO choice that is the problem. It's failure to saturate the sensor. In those situations high ISO is your friend. Don't be afraid to use it.

By the way, all this is related to the good practice of ETTR (expose to the right). If you're already against the wall on shutter speed, aperture and available (or supplementary) light then the only thing left to increase in order to ETTR is your ISO. Do it.
Click to expand...

That's interesting. Six stops overexposed and it still looks okay....

wonder how widely that applies in terms of older cameras and how they render the noise. May have to do a few experiments tonight....
 
We are saying (almost) the same thing, and the most important thing is never to underexpose. However, I'm actually going a bit further and saying that if you have headroom to raise ISO further, without causing clipping of important highlights, then you might just as well do so.

e.g. let's say that for an exposure of 1/100, f/4, 800 ISO you have a "correct" exposure - one that an incident light meter recommends, for example. But due to the tonal range of the subject/scene there is nothing at all being recorded in the brightest stop. Your approach would (I believe) be to leave the ISO at 800 and be happy with a "correct" exposure. My approach would be to kick up the ISO another stop (while leaving aperture and shutter speed unaltered) and benefit from lower sensor read noise as a consequence. I'd have to reverse the overexposure in post but I should not see more noise. If anything I should perhaps see a little less.

The wrong approach, and the one which would add to noise, would be to double the ISO but to match it with double the shutter speed. If you double the shutter speed then of course you halve the amount of light captured. It's the doubling of the shutter speed that would add to the noise, not the doubling of the ISO.
 
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specialman said:
That's interesting. Six stops overexposed and it still looks okay....

wonder how widely that applies in terms of older cameras and how they render the noise. May have to do a few experiments tonight....
Click to expand...

Not quite. The first image is nominally 2 stops underexposed, if you assume that green grass should meter at 0. The second image is only 3 stops above 0, so nominally it is 3 stops overexposed. But because it is a mid tone and was metered as a mid tone, and my camera has a clear 3 stops above 0 before clipping, then there is no (significant) clipping in the right hand shot.

If the scene had contained a range of black, white and middle grey, and I had metered the middle grey at 0 then at +3 stops the black would have become grey, the grey would have become white and the white would have been blasted off the charts, well beyond saturated and impossible to recover.

If you want to try some experiments than try a scene with a wider dynamic range (than green grass) and see how shadow noise and highlight clipping are affected by altering ISO value. That will be more revealing, I think.

I don't suppose this helps, but just to show the original exposures, and how well Lightroom did at equalising them, here are the six shots as before versions and after versions....

20110130_171908_000.jpg


20110130_171948_000.jpg


Here's how the +3 stop image looked with respect to the histogram and clipping warnings, before auto tone - just a little clipping, and not very significant. This is my idea of an ETTR exposure - perhaps 1/3 stop brighter than really necessary, but indicative of increasing the ISO as high as possible (without blowing important highlights unrecoverably)....

20110130_173443_000.jpg


I also note that Lightroom thinks that green grass should be brighter than 0 on the meter. That flies against common wisdom for metering from grass, but as all the files suffer equally at the hands of auto tone I guess that quirk is not a major factor in determining which ISO yield lower noise.
 
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tdodd said:
We are saying (almost) the same thing, and the most important thing is never to underexpose. However, I'm actually going a bit further and saying that if you have headroom to raise ISO further, without causing clipping of important highlights, then you might just as well do so.
Click to expand...

I see where we differ, I'm regarding the correct exposure as the one I consider to be correct which is already ETTR and confirmed in the histogram rather than taking the nominal zero exposure of the camera (or other) metering system.
 
Then we both agree that ETTR is the way to go. :thumbs:

Oh, and if your back's against the wall on aperture and shutter speed then you achieve ETTR by raising the ISO as high as necessary (without clipping important details). I thought that's what I said in the first place.

So in that case I think we fully agree on all counts. :D
 
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Just to put the cat among the pigeons (photographically speaking) you CAN shoot at high ISOs with almost NO noise!

Consider these pics:

This shot was taken using my 350D at 1600 ISO as experiment to achieve "noiseless" pictures at high ISO
746.jpg


Taken at 1600 ISO underexposed by 2 stops on my 350D - so 6400 ISO
805.jpg


Also taken on my 350D at 1600 ISO underexposed by 2 stops.
804.jpg

​

All of these were processed in "Neat Image" using the photos themselves to build a library of 100% profiles.

As you can see the results are exceptionally good.

I routinely use 1600 ISO now except on bright days outside.

Your DSLR can do a lot more than you know if you put pre-conceived ideas behind you and are willing to explore all the possibilities!

.
 
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Sorry Peter, but I'm not convinced. These are light images with little or no dark tones which is exactly where you'd expect to get noise by recovering from 2 stops under-exposure in processing. You can in fact see signs of noise in the moderately dark areas around the battery contacts in the last image despite the fact that you've run noise reduction?

Noise largely disappears anyway when you reduce an image in size this drastically, so the proof of the pudding with your idea lies in the full sized images - what do they look like?

Under- exposure is exactly what you want to avoid to lessen noise in an image.
 
Well this is the original of the wasp - the crop is not quite right but you can certainly see the noise even when reduced.

IMG_0746_opt.jpg


Noise reduced
746.jpg

​
And as you can see the shot was also sharpened which would tend to increase noise.

And as far as reducing an image in size I consider that also as a totally valid Noise Reduction technique - for after all who actually views an image at the original size?

And who prints an image at the original size?

And once again even if you did you'd have to stand back to see it properly which would also reduce the noise.

When was the last time you pixel peeped an advertising hoarding to see if it showed noise?
 
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It never is quite as simple as you might think is it?
An analogy for ISO (digital) is film speed, fortunately with digital we can change ISO for every shot.
There is a 'best setting' for ISO which varies from 100 to 200 (a lot of the new DSLR's now work best at 200)
This ISO setting gives the maximum dynamic range for the sensor, and therefore (under normal circumstances) should be the default setting.
With good lighting, we can increase the ISO in order to get a faster shutter speed (without noise being too obvious).
Unfortunately, when we increase ISO, all we are doing is increasing the amplification on the output of the sensor (at this point the signal is analogue).
This increase in amplification, also amplifies the noise. Noise is ALWAYS present to some extent.
In good light, as has been demonstrated, we CAN increase the ISO without it adding too much to the noise, here, correct exposure is critical, more so than at lower ISO.
Where we really suffer is when we up the ISO to get a shot, where the ambient light level is low, the amount of noise becomes effectively greater because we have a lot less photons to play with, so the ratio between them becomes less.
Exposure now becomes a ballancing act of apperture, shutter speed and ISO.
You have to decide for yourself, is the shot worth it even if there is an increase in noise?
Bearing in mind the progress made in PP noise reduction, it can expand our capabilities somewhat.
Low light is where the real problem lies, not ISO, If you predominantly shoot in low light, it makes sense to chose equipment that works best in these conditions.
For most of us it becomes a compromise, and unless you have lenses that can get down to F2 or less, these conditions can be more than challenging, to say the least. (note, I didn't say impossible!).
Now! while Auto ISO might appear to be the obvious setting, manual gives YOU control over the exposure, sure, you do have more work to do (another variable to think about) but YOU the photographer, should be in control of the variables depending on the type of shot your taking.
Auto ISO isn't bad per say, it has it's uses, it's just taking some of the control away from the photographer.
We analyse a shot before we take it, we set apperture for the depth of field we require, we set the shutter speed to match the action, we should ALSO consider ISO to enable the best combination of the other two for our shot. If it all comes together, give yourself a pat on the back, it's all down to you.
 
Peter, I quite agree about pixel peeping full lmages, but that's really the only way to judge the amount of noise in the image as it lessens the more you reduce it in size and thank goodbness it does.

You're missing the point though mate what we need to see is a 100%crop (1:1) portion of the full sized image. I regularly shoot at 800 ISO pretty much by default and don't hesitate to shoot at 1600 ISO without seeing any objectionable noise, certainly no more, and often less than is visible in your reduced image and mostly using a straightforward metered exposure.
 
I'm feeling a bit sorry for the OP actually, who asked a fairly basic question and must now be starting to bleed from the ears. :D

Anyway, this a a 3200 ISO shot with the 7D - full frame and reduced to 800 pixels. It will just have had moderate sharpening for the size reduction, but no other processing....certainly no noise reduction.

4315248495_209e403913_o.jpg


This was a straightforward shot as metered and I don't see how under-exposing it by 2 stops would add anything except noise, potentially anyway, in the recovery. I no longer have the raw image but I've no doubt the full sized file would have been pretty horrendously noisy.
 
Ok, this is all great stuff and to simplify this is what I have decided to do regarding ISO (in Av for stationary subjects):
1. Have default ISO set to 200.
2. Set desired aperture
3. As long as I can hold the camera steady at the generated shutter speed (say over 1/80) leave the ISO alone at 200.
4. If the shutter speed drops below this then up the ISO one increment at a time until I get a shutter speed at 1/80 or higher.
5. Take picture.

Can I restate that I am a beginner and I know that there is a lot more that can be done and to some of you my above five step plan will seem over simplistic but I think that it will give me a least a starting point to look at the relationship between ISO, Aperture and Shutter Speed, moving me away from just leaving ISO set to auto and not giing it another thought. I'm now off to consider how this would apply to shooting in Tv and try and find out about this ETTR malarky.

Thanks all
 
tdodd said:
Yeah, sorry, that probably was a bit heavy going for a "beginner", but basically you've got it. Use whatever ISO you need to get a good exposure in camera rather than trying to brighten an underexposed image later on.
Click to expand...

Surely not Tim ;) :D

Dead right of course, collecting the maximum number of photons is key - basic expose-to-the-right theory. But reducing ISO will, in practise, reduce noise because it forces you to use a longer shutter speed and lower f/number to compensate, and therefore collect even more light.

Noise is one thing, but dynamic range is another, and photon collection from darker tones is crucial to that. IMHO, this is the biggest benefit of ETTR technique - enhanced shadow tone separation and detail, rather than just improved noise.

And then there is sharpness, which is always better at low ISO.

Of course it's always a compromise and the reality is that you can't have it all ways, but for best image quality in every aspect, shooting both at lowest ISO and filling the histogram with a nice big lump on the right hand side, is the way to go.

Tim, on a slightly different tack, I'd be interested in your view on this. When you back's against the wall and you have to choose, in terms of image processing and sensor gain etc, what is the fundamental difference (if any) between under exposing and pulling up the Raw file in post, or raising the ISO and letting the in-camera Raw processor raise the gain that way? (Given that the basic exposure in terms of shutter speed and aperture would be the same in both cases, and therefore the photon collection would also be the same.)
 
yoshimi said:
Ok, this is all great stuff and to simplify this is what I have decided to do regarding ISO (in Av for stationary subjects):
1. Have default ISO set to 200.
2. Set desired aperture
3. As long as I can hold the camera steady at the generated shutter speed (say over 1/80) leave the ISO alone at 200.
4. If the shutter speed drops below this then up the ISO one increment at a time until I get a shutter speed at 1/80 or higher.
5. Take picture.

Can I restate that I am a beginner and I know that there is a lot more that can be done and to some of you my above five step plan will seem over simplistic but I think that it will give me a least a starting point to look at the relationship between ISO, Aperture and Shutter Speed, moving me away from just leaving ISO set to auto and not giing it another thought. I'm now off to consider how this would apply to shooting in Tv and try and find out about this ETTR malarky.

Thanks all
Click to expand...

I don't think your plan is overly simplistic. I think we all need to remember that our advice needs to be pitched at the level of the person asking, and that's a not a put-down for you at all, you need to get your head around the basic principles and get a grasp of the more technical aspects in your own good time - sensory overload isn't a good thing at the stage you're at.

What sort of stuff are you intending shooting?
 
HoppyUK said:
Surely not Tim ;) :D

Dead right of course, collecting the maximum number of photons is key - basic expose-to-the-right theory. But reducing ISO will, in practise, reduce noise because it forces you to use a longer shutter speed and lower f/number to compensate, and therefore collect even more light.

Noise is one thing, but dynamic range is another, and photon collection from darker tones is crucial to that. IMHO, this is the biggest benefit of ETTR technique - enhanced shadow tone separation and detail, rather than just improved noise.

And then there is sharpness, which is always better at low ISO.

Of course it's always a compromise and the reality is that you can't have it all ways, but for best image quality in every aspect, shooting both at lowest ISO and filling the histogram with a nice big lump on the right hand side, is the way to go.

Tim, on a slightly different tack, I'd be interested in your view on this. When you back's against the wall and you have to choose, in terms of image processing and sensor gain etc, what is the fundamental difference (if any) between under exposing and pulling up the Raw file in post, or raising the ISO and letting the in-camera Raw processor raise the gain that way? (Given that the basic exposure in terms of shutter speed and aperture would be the same in both cases, and therefore the photon collection would also be the same.)
Click to expand...

ISO in itself, has nothing to do with sharpness of an image.
It is the effect of trying to reduce noise by the processing software that reduces the sharpness. The heavier the processing, the more the sharpness is reduced - best illustrated with the average compact camera.
 
HoppyUK said:
. But reducing ISO will, in practise, reduce noise because it forces you to use a longer shutter speed and(?) lower f/number to compensate, and therefore collect even more light.
Click to expand...

You been on the sauce again Richard? :D
 
Howi said:
ISO in itself, has nothing to do with sharpness of an image.
It is the effect of trying to reduce noise by the processing software that reduces the sharpness. The heavier the processing, the more the sharpness is reduced - best illustrated with the average compact camera.
Click to expand...

Well, yes and no. Noise is redundant pixels, so you are thowing away fundamental sharpness there. And then when you try to process them away, the software attempts to fill them in with a) approximated replacements which do not put any detail back, and b) a general smearing of the image to further conceal them.

Either way, the result is lost sharpness. Dramatically so in some cases, as you say.

CT said:
You been on the sauce again Richard? :D
Click to expand...

Erm, no... What did I say?
 
HoppyUK said:
Tim, on a slightly different tack, I'd be interested in your view on this. When you back's against the wall and you have to choose, in terms of image processing and sensor gain etc, what is the fundamental difference (if any) between under exposing and pulling up the Raw file in post, or raising the ISO and letting the in-camera Raw processor raise the gain that way? (Given that the basic exposure in terms of shutter speed and aperture would be the same in both cases, and therefore the photon collection would also be the same.)
Click to expand...
I don't have the technical knowledge to explain why this occurs, but as you raise ISO, at least up to a point, the read noise from the sensor reduces. This is why raising ISO (while capturing just as many photons by retaining the same shutter speed, aperture and lighting, actually reduces noise and increases SNR. This is also why some cameras can deliver greater dynamic range at 200 ISO than at 100. It's because the read noise diminishes proportionally faster than the reduced photon count from the lowered exposure.

Roger Clark, scientist and astro-photographer amongst many other disciplines I'm sure, has gone to great pains to study the sensor performance of many cameras. In fact I even supplied him with data from my 50D when it was brand new on the market. As an astro-photographer the noise performance of sensors is of special importance to him.

He has tabulated and graphed the data from these cameras and the results, along with a wealth of other material, can be found on his website.

The specifics of sensor performance measurement are here - http://www.clarkvision.com/articles/index.html#part_4 - and results for the 7D in particular are here - http://www.clarkvision.com/articles/evaluation-canon-7d/index.html.
 
HoppyUK said:
Erm, no... What did I say?
Click to expand...

LOL. You said that reducing ISO wil result in a longer shutter speed AND a smaller aperture number .Assuming you reduced ISO from 200 ISO to 100 ISO (say) woudn't that result in one stop over-exposure?
 
CT said:
Peter, I quite agree about pixel peeping full lmages, but that's really the only way to judge the amount of noise in the image as it lessens the more you reduce it in size and thank goodbness it does.

You're missing the point though mate what we need to see is a 100%crop (1:1) portion of the full sized image. I regularly shoot at 800 ISO pretty much by default and don't hesitate to shoot at 1600 ISO without seeing any objectionable noise, certainly no more, and often less than is visible in your reduced image and mostly using a straightforward metered exposure.
Click to expand...

Well since those shots were taken using a 350D with 8MP and you have a 7D with 18MP and a 50D with 15MP I'm not surprised that when reduced in size you have less noise then a 350D.

I have now bought a full frame 1Ds mkII with 16.7MP and also excellent resolution at 1600 ISO and 3200 ISO which other cameras lack (even the 5d Mk2) and so hope to see what I can do with that!

.
 
petersmart said:
Well since those shots were taken using a 350D with 8MP and you have a 7D with 18MP and a 50D with 15MP I'm not surprised that when reduced in size you have less noise then a 350D.

I have now bought a full frame 1Ds mkII with 16.7MP and also excellent resolution at 1600 ISO and 3200 ISO which other cameras lack (even the 5d Mk2) and so hope to see what I can do with that!

.
Click to expand...

Well congrats on the new camera - I'm sure you'll see a huge improvement in noise. :thumbs:
 
tdodd said:
I don't have the technical knowledge to explain why this occurs, but as you raise ISO, at least up to a point, the read noise from the sensor reduces. This is why raising ISO (while capturing just as many photons by retaining the same shutter speed, aperture and lighting, actually reduces noise and increases SNR. This is also why some cameras can deliver greater dynamic range at 200 ISO than at 100. It's because the read noise diminishes proportionally faster than the reduced photon count from the lowered exposure.

Roger Clark, scientist and astro-photographer amongst many other disciplines I'm sure, has gone to great pains to study the sensor performance of many cameras. In fact I even supplied him with data from my 50D when it was brand new on the market. As an astro-photographer the noise performance of sensors is of special importance to him.

He has tabulated and graphed the data from these cameras and the results, along with a wealth of other material, can be found on his website.

The specifics of sensor performance measurement are here - http://www.clarkvision.com/articles/index.html#part_4 - and results for the 7D in particular are here - http://www.clarkvision.com/articles/evaluation-canon-7d/index.html.
Click to expand...

Great info as usual Tim :thumbs: Many thanks, i'll digest it later :)

CT said:
LOL. You said that reducing ISO wil result in a longer shutter speed AND a smaller aperture number .Assuming you reduced ISO from 200 ISO to 100 ISO (say) woudn't that result in one stop over-exposure?
Click to expand...


What I said was, "...reducing ISO will, in practise, reduce noise because it forces you to use a longer shutter speed and lower f/number to compensate, and therefore collect even more light." Same situation, reducing ISO means the sensor needs more light, so a longer shutter speed and/or lower f/number will be needed to deliver it.

Can't see anything wrong with that. You forgotten your medication today Cedric? :eek: :D
 
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