ETTR, iso and speed

Started by PhilippeV8, May 17, 2015, 09:55:01 AM

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PhilippeV8

Ok, the past few weeks I've been trying to get this ETTR figured out for sunset timelapse.

I still get brightness steps in my end-result and I believe I've figured out why it happens.

OK, so ETTR controls iso and exposure.  It starts at iso100 and moves the exposure gradually to the right.  If it gets to the exposure limit on the right, it moves iso to the right, thus iso200.  That's where I get the brightness step.  From what I can tell and imagine, shouldn't it move to iso200 and move exposure to the left at the same time in order to get the same image brightness before and after the step ???

Have I still got an option or setting not figured out or ... ?

dmilligan

You are always going to have "brightness steps" with ETTR. You simply remove them in post with a deflicker algorithm.

ETTR has no historicity, no knowledge of previous shots. It simply analyzes the raw data of the last captured image and sets the exposure parameters (shutter, ISO) to the most optimum values to achieve the least amount of noise, regardless of whether or not this may cause an "exposure jump".

PhilippeV8

Roger.

Altho the ettr algorithm perhaps could be programmed such that IF it shifts the iso 1 step to the right (which probably happens as soon as the exposure reaches the set limit), it also shifts exposure 2 steps left .. ?  This would greatly reduce the brightness steps, no ?  After that it can again take 2 steps to the right on the exposure before having to do another ISO step right.

dmilligan

"Shifting" as you word it implies historicity (because you have to keep track of where you're coming from).

There is no point in "reducing brightness steps" and this is not the goal of ETTR. You are basically asking ETTR to *not* do what it supposed to do. You are asking it to deliberately expose to the left, and increase noise for no good reason.

Brightness jumps can very easily be eliminated in post. There's an in-camera deflicker module, and I also wrote a script for bridge to do this. There are also countless commercial tools available.