Correct, 50 mm is close to the human eye. However, focal length figures depends on the size of the film used. The correct statement is that 50 mm focal length for a 35 mm camera has the characteristics of the human eye. The Poser focal length figures are the ones corresponding to a 35 mm camera, which is the most common type out there. If you have a digital camera, you can note that focal length figures are different, since the "film" plane there is not of the same size as a 35 mm camera. I have no idea what the correct figure is for human eye focal length, but somebody with optical knowledge can probably calculate it from the size of the retina, the eye lense and the distance between them.