subject to white background question
Nearly everything I’ve read talks about getting lots of distance between an overexposed white background and the subject or the background can overexpose the edges of the subject. Please let me know if I’m wrong, but I’m assuming that this is only relevant when not moving the camera in relation to the subject. As far as I understand, if I had to move subject and camera a few feet further away, I would end up having to increase the exposure of the background (due to falloff) and hence would be in the same situation as if the subject was closer but with less exposure……. Is that correct? Obviously, if keeping the camera/background distance constant, I can see why moving the subject would help.
The exposure of the background does not change when you move further away from it with your camera. It will only change if you take your background lights further away as well. An oversposed background will look the same from 5 or 20 feet.
When you move further away from a building, the building doesn't get darker in your photos. Same thing with your background. But when you move further away, less light coming from the background will illuminate your subject.
Hope that helps.
Zlik is right, the exposure of the background will not change as you move the camera closer or fruther.
The background is a big light source. Where the fall off of light becomes important is with the amount of light coming from the background and hitting and wrapping around the edges of your subject. This can cause overexposure of the edges of the subject so that they blend into the background.
The further from the background the lower the level of light from the background striking the subject (inverse square law) and the less problem you will have with blowing out the edges of the subject.
I recommend you keep the background to no more than 1 stop of overexposure with the subject only 6' (2m) from the background. Personally I set mine to +0.7 ± 0.2 stops.
Theoretically, if you move the subject to 10' or 12' (3.5-4m) from the background you could get the same amount of light from the background wrapping around the edges of the subject with 3-4 stops of overexposure but then you start getting noticeable broad light source lens flare resulting in a loss of image contrast. I recommend you keep the background to no more than 1.5 stops of overexposure with a subject 12' from the background.
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