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Light meter different gamma / color space (1 reply and 1 comment)

Pelle
4 weeks ago
Pelle 4 weeks ago

Hi Roger and everyone!

This might be a stupid question but, when using a light meter I'm guessing it gives the proper exposure for rec 709? How do you expose with a light meter when shooting log for instance where middle grey is set at a different IRE?

dmullenasc
4 weeks ago
dmullenasc 4 weeks ago

Most people would meter in conjunction with viewing the image with their display gamma LUT applied to the log gamma being recorded (if not raw), whether that was standard Rec.709 or some personal variant. You'd essentially let the LUT do the converting so you didn't have to think of log, and assume that the log was recording a wider range of information than the viewing LUT would display.

A common practice would be to use an incident meter for the subject and then when necessary, either a spot meter for the brightest highlights which, based on testing or experience, you knew where the clipping point was in log, or you'd switch to viewing log without the LUT on the monitor or on a waveform monitor to check where your highlights were clipping. Waveform monitors are also useful when shooting chroma key screens because you can see any extreme variations in exposure across them (though modern compositing software seems to handle this pretty well) and can set the general brightness of the screen to an IRE value that the vfx people prefer.

I can imagine someone who is extremely scientific about metering, I suppose, who uses a spot meter and knows where every value should be on in log, but most of us don't have the patience or time for that unless we are shooting visual effects and maybe need lots of values to be noted. It would be harder to use an incident meter in this case and somehow accurately convert that reading into a IRE value in log.

Personally, I think for general cinematography of dramatic scenes, that one shouldn't overthink metering, not if it starts to cause you to light for the meter and not for your eye or monitor.  It's important to think and to light creatively first and then double-check things with your meter. Of course, I'm talking about situations where you are shooting with a camera with sufficient dynamic range like an Alexa or with color negative film -- the narrower the range that gets recorded, the more careful you have to be with exposure and contrast.

Nick
3 weeks ago

When darkening an image considerably, how does one go about maintaining good contrast?

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