About exposure using S-log or C-log

illia

New member
Hi, I recently asked a question about the amount of light you need to have proper exposure using non-processed signal such as RAW and in a different way, S-log or C-log material.
The point is that manufacturers are giving some ideal IRE settings for what they believe their curves apply. For example, let's say Alexa designed the curve to have a 38 IRE when exposing a grey card.
I don't really get the hole workflow process, as I believe that this material is supposed to be color corrected to have a good image. That's also the question about how to expose if using 709 curve as a preview or to use the log output.
I recently have a bad experience while shooting a film where the footage was supposed to have been underexposed. I worked as a DIT and the lab kept on saying that the material was too dark... I kept on the Alexa spetifications and I tried to save my ass by setting the ISO to 640 and the grey point to above 40IRE... but it was still supposed to be too dark. (you may ask why I was taking those decisions while I was getting paid as a 2ndAC... but the DP seemed to be happy... that's maybe the reason why I lost my job and he didn't... but sorry for my complains!!!!)
Anyways, I knew that something in the hole workflow was strange but I think that the main season was that the lab was appying a grading LUT for filming purposes that screwed part of the Alexa dynamic range...
So the rival lab invited me to see the tests and here's what we got:
using scratch as software, the technitian seemed to be happier while having exposed the grey card to a 450 pixel value, which was the case if we exposed the grey using 400 ISO setting, , I am confused about the two opinions, as exposing a grey card to 400 ISO will give a higher IRE value than what Arri suggests... about 45 IRE (instead of 38).
Even if the hole footage was easy to recover even at 2 stops of underexposure (and we could by that use 800 ISO setting if we wanted to keep more highlight detail) I would like to know your opinion about what you think is going on once the footage gets in the hands of a laboratory... and I mean log or RAW material. Is the color corrector supposed to work with log footage or must he convert it to lineal so to grade it and then back to log to be printed?
 
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