Gelling a Reflector

[gco]

Has anyone ever put a CTB over foamcore to bounce a tungsten hard light to get soft daylight?. Seems to me it would work but that you might get twice the blue since the light would pass through the gel twice; i.e. once through the gel to the foamcore then a second time through the gel when it bounces back. In other words, a 1/2 CTB over foamcore would give you a bounced light as full CTB. Is that correct?
The obvious answer is to try it and see, which I plan to do but I am just wondering if anyone else has tried it and whether or not they got a satisfactory result.

 

[Ryan Patrick O'Hara]

Very interesting thought.

I know this is not the answer of your question.... but why not gel the light?

To attempt to answer your question... I guess technically you are right in presuming the light would be extra blue if passing through a gel and then was reflected through once again. I don't think you'll find the amount to be double blue however.

On the other hand, your gel would become a reflective surface. CTB normally has a 25% light transmission (reducing by 2 stops). Not only will it allow light to pass through it, hit the foamcore and bounce back, but it will more often be reflecting the light. Lots of light will bounce off the shiny surface without passing through the gel and leaving that light un-blued to the extent of if it had passed through.

I'm going to guess you really shouldn't worry about it, and for best results, have the CTB flush and smooth against the foamcore.

My best guess. Very interesting question. Never thought about the double blue concept.

 

[Macville]

Gelling foamcore isn't going to work very well. It's light transmission is SO soft that once you put CTB on it, you won't get any light off of it unless it's inches from your subject. Your better off getting a shiny board that's reflecting through a gel 3-5 FT away.

Now, if you don't need to color temp gel the shiny board, you can put diffusion straight on it and that works great.

Matthew

 

[gco]

Very interesting thought.

I know this is not the answer of your question.... but why not gel the light?..........

On the other hand, your gel would become a reflective surface. CTB normally has a 25% light transmission (reducing by 2 stops). Not only will it allow light to pass through it, hit the foamcore and bounce back, but it will more often be reflecting the light. Lots of light will bounce off the shiny surface without passing through the gel and leaving that light un-blued to the extent of if it had passed through.
I'm going to guess you really shouldn't worry about it, and for best results, have the CTB flush and smooth against the foamcore.
My best guess. Very interesting question. Never thought about the double blue concept.

I know, gelling the light is the first choice but it is really more of a mental exercise than anything else. I was wondering if a reflector with a gel flush against it as you suggested might make for a really fast setup when bouncing a hard light outside.

Good point on the gel reflecting. Sounds like that would give the subject both blue and tungsten at the same time. I wonder if the light loss might be double the effect as well. It's beginning to sound like it isn't going to be very effective. We'll see.
Thanks for the feedback.

 

[gco]

Gelling foamcore isn't going to work very well. It's light transmission is SO soft that once you put CTB on it, you won't get any light off of it unless it's inches from your subject. Your better off getting a shiny board that's reflecting through a gel 3-5 FT away.
Now, if you don't need to color temp gel the shiny board, you can put diffusion straight on it and that works great.
Matthew

Actually I was thinking 1/2 CTB but I see your point. Spacing the gel away from the reflector would obviously be more set up so that brings me back to square 1---gelling the source at the barn doors.
Interesting about the diffusion on a shiny reflector--hadn't considered that.
Thanks for the feedback.

 

[FBAS]

I think you're right with the thought about the light passing through the gel twice. If you white balance your camera with a 1/4 CTB in front of the lens you'll get the same as if you white balance with 1/8 ctb directly on the white card (because then the light passes through the 1/8ctb twice, giving you a 1/4 ctb.

 

[Avenger007]

This is similar to using a colored reflector. All your doing is altering the reflective color. You just have to watch how much gel your using as it can cut it too much after bouncing/reflecting. This works great for tight shots that don't permit bulky gels on lights but can easily lay flat on the reflector. Its also great if you want the key to stay strong but the fill to have a different color to it.

Heres an example. I was working on a shoot for coke that had the subject holding the bottle. To shimmer the "cold" bottle an accent light was placed on the bottle for extra definition then a gel (CTO) was placed on the adjacent reflector to give the inside/backside of the bottle a golden shine. If the gel was placed directly on the light, it would have turned the whole bottle orange/gold along with the spill onto the subject.