that's pretty darn large. I'd turn it horizontally, then angle it much shallower than 45° from camera axis. If you have a meter, can play with the angle until all three subjects meter the same. there used to be this cool video about setting up and metering for such shot -- but I've never been able to find it again. You can always take three shots in a row with you standing in three different spots and comparing the brightness of your image in each. here #10:

It will depend in large part on how you pose them and whether you plan to shoot full body, torso, or head & shoulders. 40x56 is a decent size, but lighting multiple people with a single light is probably not going to produce very interesting or exciting light. How do you plan to manage hair, background and fill lighting?

Light has a "fall off" problem based on distance. This follows the "inverse square" law. If you've got three models and only one light... the challenge is not if the box is big enough... but how far away are the models relative to the box. If you've got a model 5' away, another 7' away, and another 10' away... here's what will happen. Suppose you get the right amount of light for the model positioned 5' away. The model 7' away will get exactly half as much light... they'll appear darker. The model 10' away will get exactly half as much again (or 1/4 as much as the closest model) and they'll appear MUCH darker. Anytime the distance changes based on a factor equal to the square root of 2 (in photography that value is usually rounded to simply 1.4 but the real value is an irrational number that goes on and on), the photons of light spread out enough that the number of photons per square inch will be exactly half. 5 x 1.4 ≈ 7 7 x 1.4 ≈ 10 I used the ≈ (approximately equal to) symbol. But if you really used the square root of 2 (not just a rounded value of 1.4) then the square root of two... squared... IS "2" (exactly). And 5 x 2 is 10 (exactly 10). In photography the rounded value of "1.4" works because if you use that, you probably will be within 1/10th of a photographic stop (so much so that it wont even be worth adjusting to a 1/3rd stop increment of exposure). So it's "close enough" for our purposes. See: Anyway... if you want all three subjects to have roughly the same amount of light... then they all need to be at roughly the same distance from the light source (OR you'll need more than one light source.)

That's a good tip! BTW, you can force the video to start where you want by adding the URL parameter "=18m30s" Here's an example: And this will start exactly where you want.

ah thanks. I've seen the video you've posted too, and I was going to just link that if all else failed