Filtering the Lights vs Filtering on the Camera

[Rodrigo Prata]

Suppose you are only using one reflector to light your scene, in a controlled ambient. Is there any theoretical diference between adding A FULL CTB gel on your light and using a 80A filter on your camera?

I know it should give you the same result, but with the first case, you are altering the light before it hits your object (suppose it's a human face) and in the second, you are altering it, after it has hit your object.

Could it be that, by filtering your light source, you are also messing with what the skin is reflecting , in a different way that your 80A filter would?

Thanks!

 

[ericyoung]

In theory the absorption characteristics of a Full CTB gel will differ in some way from an 80A glass filter because the colour dyes in both will almost certainly be different.

But they should be close enough for most practical purposes. Assuming the transmission spectrums of the gel & glass filter are similar (both designed to "correct" tungsten to daylight), they will alter the ratios of blue to other light frequencies in a similar way whether that's before the light hits skin, or after. The decision might often be dictated by how many light sources have to be gelled, and how accessible they are, as opposed to one filter on the camera.

I wouldn't worry too much about this except in certain critical colour situations like shooting fashion, brand colours, or makeup, where the slight differences in dyes might subtly affect colour rendition. Then the best way is to test it yourself with the actual models or products in the same exact conditions you are intending to shoot.

 

[David Mullen ASC]

Doesn't really matter but generally except on stage or in a night interior, you have more light sources than the single key you are adding, so a camera filter would affect those secondary sources as well but a single gel on one light would only affect that light.

If you were talking about CTO gels versus 85B filters, an alternative to a camera filter would be to add the warmth by using a higher color temperature setting in the camera, which also has the advantage of improving the noise in the blue channel compared to filtering the image to a lower color temperature.

 

[Rodrigo Prata]

Thanks David and Eric!