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Will gelling a sodium vapor light change CRI


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#1 Albion Hockney

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Posted 14 January 2015 - 04:22 PM

For night exteriors i have usually gelled tungsten lights to get them in the ballpark of sodium or other low CRI city lights.

 

I'm curious if light sources which are inherently give a very low color spectrum will be give a broader spectrum if gelled properly

 

 

for example can I put a little Minus Green and CTB on a sodium light to make the strong color a little more subtle.


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#2 David Mullen ASC

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Posted 14 January 2015 - 04:51 PM

No, a filter by definition only removes wavelengths, it can't add missing ones.  So if you put a magenta gel on a partial spectrum source that only has a few color spikes in the green and orange range, mostly what you do is make it dimmer, it doesn't get less green, there aren't opposite wavelengths that become more prominent as a result.


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#3 Albion Hockney

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Posted 14 January 2015 - 06:04 PM

Ok makes sense! thanks much.


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#4 Dennis Couzin

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Posted 22 January 2015 - 11:30 PM

Every cinematographer's kit should include a spectrometer.  I used to recommend a Zeiss pocket spectroscope, but hand-held, self-contained spectrometers are now available for just $2000.  These instruments show you what's cooking in the suspect "white" light.  So you know when two are alike, when filtration might be possible, etc. 


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#5 Stuart Brereton

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Posted 23 January 2015 - 12:53 AM

 self-contained spectrometers are now available for just $2000.  T. 

 

Only $2000? Wow, I had no idea they were so cheap...


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#6 John E Clark

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Posted 23 January 2015 - 05:43 PM

 

Only $2000? Wow, I had no idea they were so cheap...

 

There's always this sort of solution... One I've been meaning to do when I have some 'spare' time...

 

http://publiclab.org...rometry-kit-3-0

 

For those who have middle schoolers in the house, this would be a good science fair project.


Edited by John E Clark, 23 January 2015 - 05:44 PM.

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