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Incident Light Meter


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#1 Alex Wuijts

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Posted 19 October 2007 - 04:00 AM

I can't quite seem to figure out how an incident light meter translates an amount of light to a suggested f-stop and how 18% reflection relates to this. Anyone here who can straighten this out for me? By the way, I don't mean 'how do you use an incident light meter?', I'm looking for a (simplistic) technical answer and can't find it anywhere on the internet.

Very much appreciated,
Alex
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#2 Kevin Zanit

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Posted 19 October 2007 - 04:23 AM

It has nothing to do with reflected light. An incident reading simply tells you that to expose 'x' amount of light falling on the dome (incident light) at middle gray (18%), use 'y' f-stop.
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#3 Alex Wuijts

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Posted 19 October 2007 - 04:41 AM

It has nothing to do with reflected light. An incident reading simply tells you that to expose 'x' amount of light falling on the dome (incident light) at middle gray (18%), use 'y' f-stop.


Thanks for the quick answer, Kevin! Somehow the most simple things can be hard to grasp at times.
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#4 Walter Graff

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Posted 19 October 2007 - 07:42 PM

Thanks for the quick answer, Kevin! Somehow the most simple things can be hard to grasp at times.



Then of course there is the 18% grey myth.
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#5 Kevin Zanit

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Posted 19 October 2007 - 08:03 PM

Ok, insert 12% gray where I said 18, but for the sake of not being confusing I am still going with what most of the world uses when referring to middle gray, 18% (in spite of the ANSI standard).

If I remember correctly, gray cards are still printed in 18% gray.
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#6 Walter Graff

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Posted 19 October 2007 - 08:24 PM

I've always enjoyed the real story that most are not familar with and thought I'd open the door to it. Here is an article I found that explains it well.

http://www.bythom.com/graycards.htm
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#7 Jonathan Bowerbank

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Posted 19 October 2007 - 09:28 PM

In that article, he said the issue was brought up in a Digital camera forum. Is it possible that DSLR meters and 35mm SLR meters are calibrated for different grey values? Could it be that DSLR's read 12% as middle grey to save you from overexposure, preserving more information in the digital image?

Just puttin' these questions out there :)
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#8 Alex Wuijts

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Posted 27 October 2007 - 04:49 AM

In that article, he said the issue was brought up in a Digital camera forum. Is it possible that DSLR meters and 35mm SLR meters are calibrated for different grey values? Could it be that DSLR's read 12% as middle grey to save you from overexposure, preserving more information in the digital image?

Just puttin' these questions out there :)


That would make sense, but my Sekonic 558 cine manual mentions a Calibration Constant (K) of 12.5 as well. My 18% world is collapsing before my eyes ;)
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