Mu-43 Top Veteran
- May 23, 2015
Your scenario (max. achievable aperture and shutter speed) depends on the camera.Please forgive me for butting-in when I know that I don't know what I am talking about. ... But if I set the shutter speed at the slowest that the conditions allow. And I set the aperture to give me sufficient depth of field (this could be the maximum aperture of the lens), so both shutter speed and aperture are predetermined for the shooting conditions, then the "correct" exposure must be set by choosing ISO. If I am now to bump the exposure in order to achieve ETTR, the only way to do that would be to increase ISO (as my shutter speed and aperture are predetermined as I described above). But increasing ISO would increase noise, but then what I understand (or don't understand) from the reasoning above is that this would result in lower noise in the shadows once the exposure is brought down in post processing even though I used a higher ISO in shooting to obtain ETTR?
Also I don't see how one can increase exposure without increasing ISO if one started from the assumption that one is already using the largest appropriate aperture (given need for depth of field) and the slowest shutter speed (consistent with getting a sharp image) in order to be able to use the lowest ISO for the shooting conditions (light, movement). Again, sorry if I am being too naive.
If noise added by camera electronics is (nearly) constant - the same at every ISO ("ISOless camera"), then your results will end the same.
For majority of M43 cameras there is a clear advantage of raising ISO as it gives you less noise in the shadows/blacks (most M43 cameras are not ISOless).
But of course one must always be aware of possible clipping of highlights with higher ISO setting.
Difference between changing aperture/shutter speed and ISO is that first two are changing signal and second is changing read-out noise of camera so both are changing signal-to-noise ratio albeit with different magnitude for different parts of image.
Increasing signal is always better choice as it leads to improvements in every part of image (highlights, midtones, shadows). Every +1EV change in the signal gives you 41% larger SNR.
Changing ISO has visible effects only in the shadows as that's only part of image where camera's electronic noise dominates and even there improvement will be less pronounced than in the case of changing signal.
Here is an example for M43 cameras with Sony's 16Mpix sensor (EM10 series, E-M5I/II, EPL series). Aperture and shutter speed were constant, only ISO was changed. In case of newer 20Mpix cameras, improvement will be less visible (at least according to photonstophotos web).