Quote Originally Posted by NB23 View Post
... But my question was why exactly is 80mm (or 100mm) better then 60mm (or 50mm) for 6x6? I understand that each focal length is optimized for a given enlargement ratio (10X, for example) and in accordance with the height of the head itself, but if the height of the head is not a problem then why would 80mm be better then 50? What is the real reason behind this? Because saying that a 80mm lens is sharper then a 50mm lens is not true. Besides the ease of use and keeping the ratios sensibly the same why would it be bad to use a 60mm lens for 6x6 format?
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Much of it relates to the coverage angle of a lens. Using a 60mm for 6x6 is pushing into a wide angle situation which makes the design more difficult and less affordable. A wide angle lens may lead to softer focus and distortion toward the corners of the image, or as M. Lointain suggests, may get away from optimum performance of the lighting and condensers.