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My first DSLR was a Canon 300D. ISO 100 was clearly the best. 200 was very noticeably worse and 400 worse again. I would use 200 or 400 reluctantly if they were the only way to get the shot. 1600 was a waste of time.

Next was a Canon 60D. It was better but ISO 100 was still noticeably the best.

Now, I have a Canon RP and it is very much better. I am wondering whether there is any detectable benefit of 100 verses 200, 400, or even a bit higher. If I want optimum image quality, and other factors allow it, should I still use 100 or would I lose nothing by going a bit higher? Maybe I would gain more by reducing any shake or subject movement with a higher shutter speed than I lose by raising the ISO.

It has been commented that my question seems a bit contradictory and that is reasonable so I will try to explain further.

I am discussing stills not video.

The lighting is good, I have selected most parameters e.g. lens, focal length, and aperture. Now, I have to choose shutter speed and ISO. Suppose that 1/100s at ISO 100 is suitable then so is 1/200 at 200 and 1/400 at 400. Camera shake and subject movement is unlikely so there is no strong need for a high shutter speed. However, the quality loss of going to ISO 200 or 400 is not obvious on my RP (unlike earlier bodies). So, it is a difficult choice.

None of the choices will be bad but which is best is not obvious. I wondered whether the noise might plateau above 100 ISO so I was gaining nothing by going down that low. If that were so, then although there is no strong need for the higher shutter speed, it still might be the better use of the flexibility that I have.

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  • \$\begingroup\$ I am trying to figure out what you are really asking here... If you have a scenario where 1/100 @ ISO 100 and 1/400 @ ISO 400 will both get you the desired exposure, and you have no concerns around camera shake or stopping motion, then you want to know why you shouldn't use ISO 400? I am just left wondering why you should use it - if there's absolutely no reason to ¯\_(ツ)_/¯ \$\endgroup\$
    – osullic
    Jul 17, 2023 at 10:19
  • \$\begingroup\$ The scenario is that there is little difference between these settings but little does not mean none. Even with a good set-up, some camera shake or subject movement could occur. So, if the quality loss of the higher ISO was none then it would be worth using, On the other hand, if the quality loss was significant then it might not be. \$\endgroup\$
    – badjohn
    Jul 17, 2023 at 14:02
  • \$\begingroup\$ Or another way: is there any quality loss at all between the low ISO settings? It could be that the sensor natively works at a ISO higher than 100 and the lower settings are achieved in software as people expect to be offered 100. Certainly in the future, a day could come when ISO 100 was ridiculously low. \$\endgroup\$
    – badjohn
    Jul 17, 2023 at 14:05
  • \$\begingroup\$ Of course the quality loss is neither none nor significant, with a modern camera. But nobody can really tell you - this is subjective. What have your tests shown you so far? Romeo mentioned the concept of base ISO - maybe this is all you need to know? \$\endgroup\$
    – osullic
    Jul 17, 2023 at 14:19

4 Answers 4

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If you want to get picture with minimum noise (best quality) you should use minimal standard ISO of your camera. Which is 100. For this ISO the signal from sensor is not amplified (to "increase" sensitivity) so you get as I said minimum amount of noise. Some time this also is named base ISO.

You can use these links to compare the high ISO quality. Unfortunately I did not found direct comparison between 60D and RP
https://www.dpreview.com/reviews/canoneos60d/17
https://www.dpreview.com/reviews/canon-eos-rp-review/4

but you can use intermediator (camera which exist on both pages like 5D Mark III)

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  • \$\begingroup\$ Thanks. Yes, in general, I would expect that lower ISO would mean less noise but I wondered whether there was a point where the improvement flattened out or became negligible. Unlike my previous bodies, the degradation up to 400 is hard to detect. A comparison to the 60D is not important. The 60D has been sold and the RP is clearly better. \$\endgroup\$
    – badjohn
    Jul 15, 2023 at 19:29
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    \$\begingroup\$ @badjohn, about the point: it depend of your acceptance of noise. In some cases for me is acceptable ISO 3200, sometime the case is have photo with noise of do not have it at all :) \$\endgroup\$ Jul 15, 2023 at 19:41
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    \$\begingroup\$ Yes, that I know and I have shot a number of times at 1600 and even occasionally at 3200 for that reason. Noise is noticeable but not terrible at 1600; certainly much better than no picture and also better than risking camera shake or subject movement with a low shutter speed. However, my question relates to the case when other factors do not force a high ISO. \$\endgroup\$
    – badjohn
    Jul 15, 2023 at 20:00
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The base ISO of a camera's sensor is the ISO setting where the sensor's signal is unamplified. It is typically the lowest value of the ISO range (but watch out for "extended" ISO values – consult your camera manual).

The base ISO offers the lowest levels of noise, the broadest dynamic range and the best image quality – even in modern cameras where manufacturers have done a fantastic job of making higher ISO settings capable of more than satisfactory results. You should aim to use the base ISO setting when you have enough light in the scene.

However, use a higher ISO setting if you need to – that's what they are there for. As said, modern cameras are capable of producing excellent results at higher ISO settings. The "limit" of how high the ISO can be increased and still produce acceptable results is going to be subjective though.

My personal preferred way of shooting is using M mode in combination with "Auto ISO". I generally set the aperture I want, and adjust the shutter speed "on the fly", letting the camera set the ISO according to how it meters the scene. (Exposure compensation is there also if I need it.) I'll favour a slower shutter speed (taking into account what's hand-holdable), so that the camera chooses a lower ISO setting. If I ever get to the point where the camera can't choose a "low-enough" ISO, then I simply set a faster shutter speed. But at the end of the day, a well-exposed, sharp photo at a higher ISO setting is always going to be preferable to a photo flawed by underexposure or camera shake.

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as all those answers are not wrong, in practice they become more irrelevant in my opinion. New sensors and especially the new "R" bodies of canon are relatively iso irrelevant. What that means in practice, the amount of noice and loss of dynamic range loss, in higher ISO becomes hardly noticeable. I do not know what kind of imaging you do, BUT, I rather have a "unshaken" pinsharp shot taken at Iso6400 than a somewhat shaken one at 400! ISO is highly overrated with modern sensors. Take a shot in iso 100/ 400/1600/6400 and look at the shadow parts, how much grain you can see in a A4or A3 printout. Iso noise is EASY corrected in post process, a shaken picture you can't!

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"(if) other factors allow it" and "reducing any shake or subject movement with a higher shutter speed" seem contradictory; if you can't have shake you need the faster shutter.

If you're at a studio w/ flashes or a sunny beach, there's seldom a good reason not to use 100 unless your flash is low on battery. If you're shooting telephoto birds or doing astrophotography without a star-tracker, camera shake will be far more detrimental than noise. If it's an otherwise-perfect candid of a loved one shot at ISO 3200, nobody's going to care about a little grain; after all, a lot of artists add grain in post to make a "filmic" look many people get all warm and fuzzy about.

Engineering (and photography) is the art of picking compromises, and we can't possibly cover all shooting scenarios. But if you're asking something like "I accidently shot something at iso 400, is it worth re-shooting at 100?"; then surely not.

Also I should add that when shooting video, you're shutter is locked to 1/50, so you usually need to adjust ISO (often to 50 or 100) to get proper exposure and bokeh/DoF outside.

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  • \$\begingroup\$ I added a clarification. Please look again. \$\endgroup\$
    – badjohn
    Jul 16, 2023 at 8:06

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