Why 'more or less stopped using ISO'?

Started Feb 19, 2014 | Questions thread
bobn2 Forum Pro • Posts: 55,085
Re: Why 'more or less stopped using ISO'?

edhannon wrote:

Which cameras do not change the content of the raw file when you change ISO without changing exposure (f-stop & shutter speed)? All that I am familiar with change the brightness.

All of the discusions about using bzse ISO and brightening in PP only talk about the impact to noise. The arguement is that, since SNR does not get better with increased ISO with the ISO-less cameras, you a re better off doing brightening in PP.

This ignores the potential for posterization when you push in PP. The curve of ADU wrt exposure in stops is exponential. The curve is very flat in the shadows and steep in the highlights. When you push by more thsn a couple of stops you loose a lot of bit re solution.

IMHO the best approach is to expose with as much light as you can and use ISO brightening to bring the highlights up to just short of saturation.

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I like to distinguish between 'P' and 'PP'. The point is that you set up your processing to get the brightness you want, not that you process for the 'ISO normal' brightness and then brighten in post-processing. That way, you can't ever get 'posterisation' - the reason being that you are never using any 'bit resolution' that was not there in the first place. In fact, using the in camera gain (if your camera isn't 'ISOless' doesn't provide any more 'bit resolution' - all it does is shift the signal to use more significant bits, clear of the noise generated late in the digitisation chain, which can sometimes occupy as much as the three lower bits.

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