Quote Originally Posted by John Koehrer View Post
I'd argue that in most circles the diagonal of the film is the determent factor in defining "normal" not focal length..

4X5"=135mm etc.
Yes. What makes the 50mm range appear "normal", and a 43mm seem slightly wide, is the format. The 3:2 ratio of width to height makes the 135 frame look wider than 5:4, 4:3, or 1:1.
This is most obvious with panoramic formats. My 645, in full format of 42X56 gives a very different "look" than with the 35mm pano back with the same lens. The image with the pano back can even give the appearance of being a wide shot with the 75mm lens, a "short telephoto" length on the 135 format and "normal" on the 645.