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  • Light Meter Calibration

    Team. I know every DP has his own opinion but just out of curiousity, do you calibrate your light meter for middle grey or for skin tones (caucasian)? Thanks. Just want to see what professionals do.
    My Youtube Channel
    https://www.youtube.com/jsfilmz

  • #2
    Middle gray, Adams Zone 5 for me. Universal value reference.

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    • #3
      Same here, Zone 5 has been my calibration reference between meters and cameras, using a grey card.
      Cheers

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      • #4
        What do you mean calibrate? The factory calibration gives you the f stop for middle grey to be exposed normally when you take an incident reading. That same reading is will give you normal exposure for skin tones as well. No need to change anything.

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        • #5
          Originally posted by rze View Post
          What do you mean calibrate? The factory calibration gives you the f stop for middle grey to be exposed normally when you take an incident reading. That same reading is will give you normal exposure for skin tones as well. No need to change anything.
          I think he means the spot meter.

          Comment


          • #6
            Originally posted by rze View Post
            What do you mean calibrate? The factory calibration gives you the f stop for middle grey to be exposed normally when you take an incident reading. That same reading is will give you normal exposure for skin tones as well. No need to change anything.
            By skin tone do you mean Caucasian skin tone?
            My Youtube Channel
            https://www.youtube.com/jsfilmz

            Comment


            • #7
              Originally posted by rze View Post
              What do you mean calibrate? The factory calibration gives you the f stop for middle grey to be exposed normally when you take an incident reading. That same reading is will give you normal exposure for skin tones as well. No need to change anything.
              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?
              Last edited by jrd; 12-06-2018, 06:53 AM.

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              • #8
                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?

                I guess the real question is are you going to require every gaffer you work with to change their settings of their meter? Itís easier to test what +/- stops from factory calibrated you like, and communicate with respect to factory calibration reading how you want them to expose the scene. Again what you say sounds good on paper, but in practice on set, not very practical

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                • #9
                  hey guys. Thats exactly what im wondering about. My default sekonic light meter settings seems like its underexposing so i was trying to calibrate it with my pocket 4k so that i can get middle grey with it. Speaking of middle grey is around 384 in the resolve wave form right?
                  My Youtube Channel
                  https://www.youtube.com/jsfilmz

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                  • #10
                    My l758 is pretty spot on for getting 38% for middle grey, I would get a friends meter and See if you are getting the same readings. What IRE vale’s are u getting for middle grey when you expose for the incident reading from the sekonic?

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                    • #11
                      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.

                      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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                      • #12
                        raw.jpg
                        Here is the raw grey card. i think its sitting pretty low
                        My Youtube Channel
                        https://www.youtube.com/jsfilmz

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                        • #13
                          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, 11:21 AM.
                          My Youtube Channel
                          https://www.youtube.com/jsfilmz

                          Comment


                          • #14
                            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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                            • #15
                              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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