Film to flange distancegreenspun.com : LUSENET : Large format photography : One Thread
I recently bought a custom built 4x5 camera for aerial photography. It originally had an APO Symmar 150mm lens on it (I never owned this lens). I was trying to put a Graflex Optar 135mm lens on it and it is out of focus. Needless to say, I failed to learn anything about the film 2 flange ratio of either lens and the camera has a fixed film 2 flange distance. I can make some modifications if the distances are not drastically different, but I do not know the correct one. If this it too much trouble, how about suggesting some lenses with the same f2f as the APO Symmar 150mm.
-- Stephen Glover (firstname.lastname@example.org), August 15, 2001
-- Bob Salomon (email@example.com), August 16, 2001.
A 135mm lens will almost certainly need to be moved closer to the film (by about 15mm, at a guess).
You can measure and ponder over maker's lens data, or guess and hope at the right mounting distance all you like. The only way you'll get any lens set up properly is to fit a focusing screen at the film-plane and visually adjust the lens distance for the best infinity focus.
I'm sure the maker of this custom camera built in some small adjustment for lens focus, probably a locking screw somewhere near the lens mount. To do the job by dead-reackoning wouldn't be sensible.
BTW, if this camera takes standard darkslides, the seating for the darkslide is 4.8mm forward of the focal plane.
-- Pete Andrews (firstname.lastname@example.org), August 16, 2001.