Donald Miller said:While it is important for the condensors to spread light evenly, the primary purpose of condensors, in a condensor enlarger, are to focus the light at the nodal point of the lens.
David A. Goldfarb said:I do not believe this to be true. Unless the enlarger is designed to use only one specific lens, one format, and one enlargement size, the nodal point of the lens is moving all over the place all the time, while the condenser lenses are fixed, except insofar as you may change them for different formats.
I can make a wallet-sized reduction from a 4x5" neg or I can project onto a wall or the floor and make a huge enlargement, but I don't know if there is any condenser enlarger that requires a change in the condenser lenses for those two conditions, though the nodal point of the lens is quite different.
I had been thinking about writing earlier to describe why this would have to be done differently for same focal length lenses of varying designs, or even for different magnification ranges with the same lens as David mentions. The lenses have different designs, so nodal points (you don't specify front or rear nodal points) differ relative to focal length, and the position of the mounting threads/flange relative to the nodal point(s) is not standard across manufacturers or designs either. A Componon won't match a Componar in the same focal length, etc. This would be why Durst, if aiming for a nodal point, has to give very specific instructions for lens and cone combinations, and take into account design differences in lenses of the same focal length.Donald Miller said:David, I will be happy to send you the tables that Durst calls out for different lens manufacturers and focal lengths. In certain equivalent focal lengths of Rodagons and Componons they have different condensers specified. I assume that this is for very valid reasons.
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