Thread: Light Meter Calibration

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  1. #11  
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    Quote Originally Posted by jsfilmz View Post
    By skin tone do you mean Caucasian skin tone?
    An incident reading should properly expose all skin tones. Now, proper exposure of darker skin may place it's exposure in a noisier part of the waveform. That's where creativity and experience comes in. A light meter is just a tool.

    Quote Originally Posted by jrd View Post
    No need to change anything? Consider that

    1) digital camera manufacturers have very different ideas of what any given ISO actually means;

    2) light meters are calibrated for t-stops, not f-stops;

    3) different manufacturers put middle grey at different IRE levels. BMD says 38.4%, which is fairly typical for log. Another manufacturer, or shooting a rec 709 mode, and the value could be different.

    How is the factory calibration going to anticipate all this? Won't you need to set an offset?
    1. I've never had any issues. I suspect camera manufacturers use a light meter to decide when setting ISO values.

    2. Yes. If you're using a lens with f-stops, you compensate for that.

    3. I don't understand. Using an incident reading will place middle gray at the correct IRE. This isn't something you should have to think about. Again, camera manufacturers use light meters so that these things work the way they're supposed to. If for some reason you're not getting the right result (see below) you can compensate for that.

    None of this explains why you would calibrate to a skin tone instead of middle gray. In fact it reinforces why middle gray is the correct choice.

    Now, is middle gray 12% or 18%? And which one is your light meter calibrated to?
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  2. #12  
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    raw.jpg
    Here is the raw grey card. i think its sitting pretty low
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  3. #13  
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    Here is with a -1 offset on the light meter. This is better than the default right? This is more like middle grey and not the other?
    neg1.jpg

    Here is the rec 709 version of the -1 offset in the light meter.

    Untitled_1.1.2.jpg
    Last edited by jsfilmz; 12-07-2018 at 02:21 PM.
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  4. #14  
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    Why is the WF clipped at 512 or is that the guides? What does that pic look like? What happens when you bypass the LUT.
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  5. #15  
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    It looks like you need a slightly greater offset, since even the 2nd one is still a bit low, assuming you're shooting log. There's no clipping, that's just the grid line.
    You can use the BMPCC 4K's false color feature to make matching the meter to the camera easier. When the card is green, it's in the correct range for middle-grey.

    What meter are you using, btw?
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  6. #16  
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    Damn. I knew something was wrong with the default. That was shot with pocket 4k raw the waveform was Raw. It might be because im using the cheaper sekonic lightmeter
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  7. #17  
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    Quote Originally Posted by jsfilmz View Post
    Damn. I knew something was wrong with the default. That was shot with pocket 4k raw the waveform was Raw. It might be because im using the cheaper sekonic lightmeter
    There's no such thing as a raw waveform. The raw file was either converted to log or rec. 709 (or other display standard), depending on your settings. in the raw tab. Which is it? I don't think the cost of meter makes any difference, the sekonic should be reliable, but it may (like any meter/camera combination) require adjustment.
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  8. #18  
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    Quote Originally Posted by jsfilmz View Post
    Here is with a -1 offset on the light meter. This is better than the default right? This is more like middle grey and not the other?
    neg1.jpg

    Here is the rec 709 version of the -1 offset in the light meter.

    Untitled_1.1.2.jpg
    Theres possibly some user errors going on. The rec 709 shouldn't be creating such a blue cast, keep in mind shifting the white balance drastically will alter the exposure values of the wave form, but the exposure is correct for the -1 offset. Once you remove the cast the key light is between 40-50% IRE which is in the right ball park for your skin tone, but who knows how your lut is remapping middle grey. How exactly are you taking the readings and what are your meter settings, and how are you filming the grey card?
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  9. #19  
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    Yea sorry for not knowing the proper terms but what i meant was i left it at Raw in the camera setting tab. I think im going to leave it at -1 because its the closer to middle grey than the default 0. I pretty much held up the grey card in front of my face then placed it down after a couple of seconds.
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  10. #20  
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    Since you have more of a 3/4 side light, did you angle the grey card towards the key light? If you want to be more precise, do a front light over camera for the test.
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