Light box lighting problem

[Navaar]

I hope I've picked the right forum. My search found a thread on a different light box issue here, so I think I've picked the right one.

I've made a light box following the instructions in the tutorial. My local hobby shop has never heard of bristol board, but I got white poster board that seems like it should do the trick.

I'm using a thin white (muslin?) fabric to cover the top and sides. I have 2 100 watt full spectrum bulbs for lighting.

My problem is that no matter what I do, the shot comes out with a brown tone to the background. I have a Canon 30D and have tried shooting on both raw and the programmed macro mode. I've tried different white balance settings, as well as trying out different settings on the white balance. I just can't get the images to come out correctly. About the only thing I've found that will get the colors to come out correctly is +1.0 exposure compensation, and set the temp to 3400. It's not bad, but not as good as it could be. I feel I'm missing something, but have no idea what.

In case it's an issue of the bulbs (still researching this) I'm using GE reveal 100 full-spectrum bulbs.

Any ideas?

[zona5101]

I believe you are on the right track - it is a white balance issue that may also be compounded by under exposure.
Can you indicate the shutter/iso/aperture setting your using? Posting an image would be good as well. I am not familar with your camera, but can you set a custom white balance?

[OsmosisStudios]

Your bulbs dont matter if theyre being diffused: the fabric youre using must have a colour cast.

[oldwolf]

Things you should look at:

1. What are you using to light the background? Even with a light on the background you need to expose it for the color you want it to come out to be. You can make a white background look black with the right type of lighting.

2. If you don't have a light on the background then you need to expose the background for whatever color you want it to come out as. Again, refer to the first thing where you can make a white background look black.

3. Tint of the softbox/muslin that you're shooting through. That will color the light as well.

You're camera will try to expose for 18% grey. So white isn't actually going to look white all the time. That's when you need a longer shutter speed so that the white gets exposed as white.