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Light meter calibration with Red

sekonic light meter red scarlet calibration

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#1 Orlin S

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Posted 31 July 2013 - 01:22 PM

Hey all,

I'm a film student and i just bought a used sekonic light meter 758d. I wanted to match it with the red scarlet i'm usually using for shooting. So i set up a 18% greycard and used false colors in Redcolor3 view to match the mid grey (green color on the card). Camera was set to 640 ISO, 25 fps, 1/50, f8. After i took a reflective reading with my sekonic i found that i should set it to 320 ISO, 25fps, 180 degree, to match the f8. Anyway after turning false colors off i found the image of the greycard way darker than i expected. I also tryed to expose a skin tone on the same lighting setup (on f 5,6 to get it properly exposed) and still seemed a bit underexposed. Then i decided to try matching the light meter in Raw view. After i got green on the card with false colours turned on i swithced back to Redcolor and i had much better feeling with the image. So my first question is, am i doing something wrong to match my sekonic or is there a better or more acurate way to do it ?  Second, should i match it in raw view or redcolor3 when considering, that the clipping and crashing levels are the same in both modes ?  

 

Sry for my english :) 


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#2 Alan Rencher

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Posted 01 August 2013 - 01:42 AM

I think you may be confused on how a light meter works. You should set your light meter to the settings that you want to remain constant (ISO, shutter, etc.), then use it to give you a reading for the variable (like your F-stop). There is no calibration to the camera. The constants should be matched on the camera and light meter.

Example: you've decided that you want an ASA of 800, with a 180° shutter. Set the camera and the light meter to match, then take a reading. The light meter should then give you a reading for your F-stop (or T-stop). After that, just set the camera to match. It it's possible that your false color will read a bit differently than your light meter. This can be caused by different variables, but it's usually not that far off.

Hope this helps.
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#3 Orlin S

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Posted 01 August 2013 - 04:06 AM

Hi Alan,
Thank you for your answer. But at first place the problem was than when i took a reading with mached settings as u said i always got overexposed footage and i'm sure it was overexposed because it always left me like 2 or 3 stops before clipping, so i wanted to match and compensate on iso to get propper same f stop on the greycard.
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#4 Chris Millar

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Posted 01 August 2013 - 04:53 AM

Doesn't the 758d have a kind of programmable sensor look up table hoohah ? Is that what you're talking about Orlin ?


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#5 Adrian Sierkowski

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Posted 01 August 2013 - 06:09 AM

It does but I've never used it. What I think is that you are looking @ the raw image data, which is great, and how one would set exposure off of a RED normally to make sure you get the information you want. HOWEVER, when you toggle off of raw, you're getting the rough approximation of how it will look in the end. You say yourself that this looks about right to the light meter when you go over to redcolor, so no you're not really doing anything wrong with the meter, but you're looking at your monitor wrong. In RAW mode it's showing you a log response (if memory serves) and as such 18% grey may well be mapped lower in order to preserve highlight detail later on for the grade.

i can tell you I never use my light meter to set exposure on digital systems, specifically because of reasons like this. I need to look at the histogram/false color/calibrated monitor to really dial it in "right." Instead I personally use my meter to get lighting ratios which are mainly camera independent-- e.g. a 2:1 ratio is a 2:1 ratio no matter what camera I'm using. What'll change is how it'll read on the sensor itself but that is something you know via experience and testing.


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#6 Orlin S

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Posted 02 August 2013 - 06:31 AM

Hi Adrian,

till now i've also been using light meter as a tool for creating correct lighting ratios or for the ability to recreate same light in different time or place, but now i'm looking for the ability to guess the right exposure or amount of light needed when on location scouting. I want  to try getting more acurate when creating lighting design of the scene or the ability to use on set natural lighting sources. Anyway theres a lot of true in your post ! Today i plugged a calibrated monitor with waveform in to the camera, set the exposure same way i explained at the beginning and realised, yet it looks a bit underexposed the greycard was exactly at the 50 IRE (on the waveform) where it should be right ??? So to summarize, now when i took a reflection reading of a greycard with my sekonic and set the same f stop to my camera the greycard is exactly on 50 IRE, witch means it works correct i'm i right :) ? But thats all happening on Redcolor3 mode with Raw view turned off, when i turn raw view on it all goes wrong, including the waveform :). But what i understood from you is that i should stay with Raw view turned off when setting exposure right ?    


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#7 Adrian Sierkowski

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Posted 02 August 2013 - 09:51 AM

I always use my meter when I scout.

For myself, though, I just rough it in with this... so exact matching isn't as big of an issue.

 

 

But yes, you get it. When you're looking @ "RAW" mode on the sensor, you're seeing the scene exactly as the sensor sees it (within reason). So of course it's in no way going to match what the final picture will look like. You just want to make sure, with false color, that nothing of importance to you is clipped white or black, but for the most part from there I do not worry at all about how it looks in "raw," because it'll be corrected in post.

Hence why we monitor with LUTs, such as the RedColors or Rec which should more properly match with what you're looking @ on your meter.


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#8 Oliver Hadlow Martin

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Posted 02 August 2013 - 03:52 PM

http://www.ryanewalt...icprofiles.html

 

 

Scroll down to the profiles. Load Epic/ Scarlet settings it into you light meter. Job done.


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#9 Orlin S

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Posted 05 August 2013 - 06:52 PM

http://www.ryanewalt...icprofiles.html

 

 

Scroll down to the profiles. Load Epic/ Scarlet settings it into you light meter. Job done.

Thx ! I'll check it !


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