Quote Originally Posted by Kevin Kehler View Post
Generally speaking, when you are at twice the focal length of the lens, you will have 1:1 magnification. Thus, for a 210mm - when the bellows are at 420mm, you have 1:1
So here's a sort of adjunct to the Original Question that I've wondered.

Does it make a difference to this 'generally speaking' depending on the formula of the lens in question?
ie, as far as I know, most LF lenses are pretty well balanced, the flange distance at infinity is the same as the focal length of the lens. Eg, a Super Angulon is a Biogon-style, so a 90mm lens with the pupil 90mm from the film is focussed at infinity. Then (theoretically) 180mm from the film you're at 1:1.

But what if the lens design is a retrofocus, where flange distance is longer than the focal length (like a wide-angle on a 35mm SLR, focal length 12-35mm with flange distance of 40-50mm, or wides on MF 30-65mm with flange-distances of 70-80mm). Afaik some of the widest and latest Alpa 4x5 lenses (like anyone can actually afford them) are also retrofocus.
Or if it's a Telephoto, where pupil distance is longer than the flange distance. (are there any Telephoto LF Lenses? I know focal lengths can get huge sometimes, do those Fine Art XXL 1100mm lenses have to have a 1.1m-long bellows just to get to infinity?)