Auteur: Dan Fromm
Date: 08-11-2004 13:09
Flange focal distance? I use it to determine whether a lens can be made to focus at all on my camera. For example, the 47/5.6's FFD is too short for the lens to focus to infinity on my 2x3 Speed Graphic.
Effective focal length. In general, interesting but useless. For macro work, useful in calculating magnification given extension from the infinity position and magnification given extension.
Back focal length. In general, interesting but useless. But useful for determining whether a lens can be used on a medium format single lens reflex. For example, my 12"/4 Taylor Hobson telephoto has back focal length ~ 85 mm. Too short to work on, say, a Bronica S.
Principal point separation. In general, interesting but useless. But for macro work, useful in calculating magnification given extension from the infinity position and magnification given extension.
Regards,
Dan
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