I recently picked up a late model 4x5 Gowlandflex, and I've been testing it out in the studio. After some needed adjustments to the rack and pinion to allow for smoother focusing action, I started to test the viewing lens ground glass against the ground glass of the film holder, on which the taking lens projects the image. I assume this is the best way to check focus accuracy.
Despite the fact that everything appears plumb (using a bubble level to gage everything), the lenses, both identical 180mm Nikkor-W in Copal 1 shutters, do not focus identically. I need to rack the focus nearly 1/4" more out to get the film plane ground glass to match the sharpness of the upper viewing ground glass.
I double checked to be sure all was parallel.
I assumed that if both lenses were identical then the issue must be either be...
A) a tilted front standard. It isn't.
B) a misaligned internal reflex mirror. It seems very secure in place.
C) a misaligned or loose viewing ground glass. That looks good too, with no play. It is flush to the top of the square frame atop of the camera.
D) an out-of-whack film back. But that appears flush to camera, and secure.
E) different lens boards or mounting hardware. Nope. Both exactly the same.
I ended up shimming the taking lens out, about 1/4", to allow both lenses to throw sharp images on both ground glasses.
So the question is, can identical lenses behave so differently? Many TLR cameras do use cheaper glass for viewing, and I would expect the difference might pop up in that scenario. But with the identical same lenses in the same shutters?
Anyone with similar experiences?
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