ISO invariance understanding it - just checking something

Started 2 months ago | Discussions thread
SigZero
SigZero Regular Member • Posts: 485
Re: ISO invariance understanding it - just checking something

Brian Kimball wrote:

SigZero wrote:

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.

You've got this backwards unfortunately. Dual conversion gain tech does not impact one's strategy when they are able to overexpose. More light at base ISO is always better and will result in higher SNR. The advice to "overexpose ISO 100 no more than 2,5EV" is very misleading. For purposes of ETTR, ISO 100 can be overexposed as much as the scene allows, and more will always be better as long as you're still meeting your needs WRT to clipping, DOF, and motion blur.

Yep you are absolutely right. 
I've described it (unfortunately only in Polish) about year ago and now got it backward. You should use ISO 640 only when your exposure requires ISO 100 on -2,5 EV.  In the other direction there is no limit of course.

Thanks for correction.

Br, Pawel.

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