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Message: <blockquote data-quote="J-see" data-source="post: 404581" data-attributes="member: 31330">I have to test this during the daytime too since it can have more effect than I imagined.Take as an example when I'm birding. I'm shooting at ISO100 at f/6.3 and my shutter is maxed at 1/500s for correct exposure. What I usually do is increase the ISO, let's say 200 in this case and use that to get a faster shutter of 1/1000s and my exposure remains identical.But this is not really the case. The exposure of my end-result will be largely identical but the sensor only received half the signal because the shutter duration is halved using the same diaphragm. What the cam does is count the sensors pixel saturation and what was 1 before, now is 2. It does so too with noise and although it is less of a problem during daytime, signal noise is ever present. The accuracy of a signal measured is proportional to the size of that signal captured. For photon counting, noise seems to be the square root of the amount captured.Which means 9 photons results into 3 noise (SNR of 3) while 100 photons in 10 noise (SNR of 10). Both increase but not at the same rate. The problem with using ISO is the decrease of the signal size which inevitable leads to an increase in noise (in terms of SNR), which then also gets amplified.Now for many shots we don't have a choice. Either a shutter or aperture (or both) are required and ISO is the only option left but when not, ISO should always be last on the list. I can better underexpose as long as I can recover that in post, than up the ISO and do actually the same underexposure but with additional noise when that gets normalized. But again, it depends on the cam's sensor efficiency how far we can take this, and on the circumstances we are shooting.</blockquote>

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