120mm approximates the settings used by most fashion photography view cameras. I haven't gotten a striahgt answer about the lens size Poser assumes at default 100% scale, but the focal and lens size together actually determine the depth of field. In a traditional SLR, the aperture setting (F-stop) determines the functional lens size. From what I can figure based on the fact that a 50mm focal length approximates the human eye according to the documentation, and that an average human eye has a 9mm lens with a 17mm focal length, the lens size seems to be probably 28mm, which would lead to a 48mm focal for human eye approximation. Of course, that's only if they're right. B^)