I am using Sony FS7 - my question is - there are 2 shooting modes, custom and CineEI. will i have to treat slog3 custom material differently than slog3 CineEI material. (i am aware that in EI you can not alter matrix and other settings)
I am just getting started with using luts and luma curve etc.
Shoot a test and use color charts -- the DSC Chroma DuMonde is excellent, and the XRite Colorchecker Video is cheap but OK -- then bring the clips back into Resolve and evaluate them yourself. Try different decoding methods and see what works. The scopes will tell where you are in terms of accuracy, and the monitor will tell you if the image is appropriate for the nature of the project.
In general, I think it's possible to create these looks in the first node or two just by using curves and primaries, but you do have to at least start with the right color science. For example, with Red R3D material, I think it's good to use RedColor4 or DragonColor (or whatever is current with the camera) for color, then RedLogFilm for gamma space, and then take it from there to create a reasonable picture within Resolve. There are pros and cons with using LUTs, but in general I don't think they're necessary unless the LUT is a client request and was specifically created for that project.