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#1 amar nerurkar

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Posted 04 September 2007 - 08:55 AM

many times i read if u use day light balance film and have tungtun lights, to get proper result u have to use 80a blue filter on camera, it might cut 2and 2/3 stops of light but give true result, white as a white on the film
practically it working
cant understand conceptually
see if the light is tungtun ie CT is 32oo degK
how can u increase it to 5600 degk by using a blue filter
and secondly if u use blue filter in front of white light u got the blue coloured light from other side that means filter can allow only blue part of light that means it hides the red and green part of light
if same funda apply in this case that means if u keep blue filter in front of yellow light then there should be no light at the other end. because yellow is a mixture of red and green
but we see practically this is not happen.
please anybody tell what exactly happen in this case ??????????????????
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#2 Delorme Jean-Marie

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Posted 04 September 2007 - 11:54 AM

hi

daylight film is 5600K with 5600k light it will be white.
tungsten film is 3600K with 3600K light it will be white

if you want to achieve a white light with a tungsten projector you have 2 solutions :
- you gel yours projecyors with a full blue to cool the light from 3600°k to 5600°k
- or you cool the entire picture with a blue filter in the front of the lens
on both case the light will be white.

blue or orange are not colors in this case but temperature of color in °k which is different and rect diferent than mixing of colors

hope it helps
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#3 Chris Keth

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Posted 04 September 2007 - 05:45 PM

All you are doing is filtering a particular light source with a filter that will change it's spectral curve. If all of your light source match, but they don't match the film's needs, you can filter the camer instead of all the lights. Tungsten light has more orange and red light in it than daylight does. To get them to match, you either have to remove some orange and red from tungsten (with CTB or an 80 camera filter) or you have to remove some blue from daylight (with CTO or an 85 camera filter).
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#4 amar nerurkar

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Posted 05 September 2007 - 12:55 AM

All you are doing is filtering a particular light source with a filter that will change it's spectral curve. If all of your light source match, but they don't match the film's needs, you can filter the camer instead of all the lights. Tungsten light has more orange and red light in it than daylight does. To get them to match, you either have to remove some orange and red from tungsten (with CTB or an 80 camera filter) or you have to remove some blue from daylight (with CTO or an 85 camera filter).




u r on a right track
i got the answer of that question in spectral theory
in the spectra of tungsten light u got blue line also means it contain blue but the intensity is less comparitivly than red and orange and green.
that means 80a regulate the amount of yellow part of light and make light arrangement as a white light for day light film and so thats why there is a huge amount of light cut and so u have to open more aperture
(2 and 2/3 of stops)
thanks for the reply
have a good day
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