Why ETTR?

Started Dec 20, 2013 | Questions thread
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Ysbrand Galama OP Regular Member • Posts: 160
Re: Why ETTR?

I am still missing something. The purpose of ETTR is to improve the signal to noise ratio, so increasing the exposure time makes sense, I understand that.

But if you want to improve the S/N-ratio, why not reduce the ISO instead of lengthening the exposure time? A lower ISO has a better S/N-ratio, so the end effect is the same.

Or, worded differently: when your lense is wide-open you have two ways to increase the S/N-ratio: increase shutter time, or reduce ISO. Why is increasing the shutter time better than reducing the ISO?

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