ISO invariance understanding it - just checking something

Started 2 months ago | Discussions thread
OP CESA Regular Member • Posts: 377
Re: ISO invariance understanding it - just checking something

SigZero wrote:

Hi,

Here are some rules, not all exactly matching your scenarios, but I hope it will clear some things.

With every increase of ISO (1 EV) You are loosing around 1 EV in highlights. Overexposing to te limits of the sensor (Zebra at 109% is Your friend here) and then pushing exposure down and shadows up (which means leaving them at real exposure level) gives you the best highlight protection and shadow noise performance.

In case od dual gain sensors the key is to overexpose not more than the limit of dual-gain change. So If the limit is at 640 ISO, then overexpose ISO 100 no more than 2,5EV and overexpose ISO 400 no more than 0,5EV - of course if having best shadow noise performance is the key.

In case you need to have better shutter speed and need to overexpose more then the limit, bump ISO to second gain settings (640 in Your case) and overexpose accordingly there - You will loose more highlights but get better shadow noise.

If the situation is the other way - if in order to keep highlights you need to make negative exposure compensation - if you need to cross dual-gain boundary it is better to underexpose more on lower ISO than underexposing on higher and crossing the dual gain level (is such case You will not saturate sensor to its full capacity).

Br, Pawel.

Thank you for your comment. I think I understood. However what if I want to shoot back-lit to get some flares from the sun? I need to underexpose to preserve the highlights. So in this case because I have to underexpose it is best to go to the first gain stage, use ISO400 say and underexpose by 1 stop for example or 2 stops.

Now this means that when I recover the shadows I will be like stepping to the next gain stage? Equivalently in post? Do you know what I mean? When recovering?

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