OK, I'll answer you both. The reason the background goes orange (warm) is because you are shooting daylight film (or digital equivalent) which is rated around 5000 degrees Kelvin. Strobes are rated at between 5500-6000 degrees, which is more blue than tungsten (or incandescent bulbs) which are farther down on the color temperature scale, around 3400 degrees. (If this is a foreign language to you, study up on color temperature). So..... on daylight film, incandescent lighting comes out orange (or red to you).
The solution, as correctly pointed out, is to gel the hot lights with cooling gels, which in this case would be blue, either 80A (the correct conversion filter), or 82A (a little weaker) or something that looks good by trial & error, especially of you are using Polaroid or digital camera to test it. You could also use some plain gel of any color - pure green or red, either one will show up that way on your daylight film. Be careful that you use theatrical gel which can stand the heat of a hot lamp, but don't let the gel touch the bulb and make sure its vented. OR.... you can convert the strobes with the opposite colors - 85B on the strobe heads (vented as well, or you will melt the electronics), but then you have to use tungsten film (or I guess change you white balance in digital). Most pros would gel the hot lights, or just leave them alone. I've done this many times, as in the example below, where we did just that, but did add some warming gel to the strobe heads to balance them a little more with the warm-toned hot lights in the back. Does this all make sense?
(Hot lights on background, one large softbox strobe on Kelli McCarty, former Miss USA).
Now there are two other things to know. Obviously if you're using hot lights, you will have to slow the shutter way down to get the light to read on the film at any reasonable f-stop, especially if you want it to balance with the strobe in terms of intensity. One of the benefits (or hazards, depending on your intentions) of this is that you can get blur - and depending on how you do it, get some cool effects. If you have the camera on tripod and the model doesn't move, you get no blur. If you have the camera on tripod and the model moves (intentionally, just a bit) then you get the edging look you see here, because she is blocking the background for part of the exposure. If you move the camera during the exposure, you will get edging on the model, and blurring of the background, but the model will still be sharp because she's being exposed by the strobe. You can also have the camera on tripod, make the model hold still, and move the background (if its fabric or a flat) for another kind of blur. Personally, I prefer it with slow shutters to blur everything except the model. By the way, this works outdoors with strobe as well.
As for the last question about how to keep the main strobe from bleeding onto the background and infecting the color, the answer is simple - keep the background at least 10 feet from the foreground, so you end up lighting them seperately. I use a rule of thumb (which I got from a Dean Collins seminar many years ago): Turn off the background lights, then (incident) meter the foreground using only the main light, then meter the background using only the same foreground main light. If the falloff to the background is at least 3 stops, you will get no (or very little) contamination from the main light into the background. We did this for years for one client, where we routinely changed background colors using only gels, and it went very fast, and the colors were always saturated with no bleed from foreground to background, or vice versa. Below is one of those of Pamela Anderson.
And yes, these are old images. Just happened to be the easiest/best samples to find. You can tell they're old, they were done in my "torn jeans and bra" period. Come to think of it, that's still a good look.
Regards,
Andy Pearlman
Andy Pearlman Studio
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