What this tells us is that the further away the light source is from the subject and backdrop, the more likely we are to get an equal exposure from one to the other. The quality of the light source can also change with distance. You will notice that as the light gets further away it becomes a harder light with less transitional values. Also, if the subject appears to be further away from the backdrop in the last image, it's due to me needing to use a shorter focal length (zoom out) to avoid getting the softbox in the shot. The shorter focal length exaggerates perspective.
In the shot above I used a two light setup. The main light, camera left, is a Profoto D1 1,000Ws head inside of a 50 inch Westcott Apollo Softbox. While the idea of mixing what is considered to be a high-end strobe with a budget softbox my not sit right with some, I find the indirect lighting source from a Westcott or Photek to give a really nice and even light. The 60 inch Photek Softlighter, which I also enjoy using, may only cost $95 but gives a really nice, soft, and even light. If these lower cost indirect sources are good enough for the likes of Mario Testino and Annie Leibovitz, then they are good enough for me. Clay Cook did an great article on these lighting sources, "Lighting Like Leibovitz," that you can find here.
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