Doug Kerr
3-Jan-2007, 16:05
I recently acquired a nice Rodenstock Apo-Ronar 480 mm f/9 barrel lens.
The aperture ring is conventional, but it has a second scale, calibrated in mm, which seems to give the exit pupil diameter! (Perhaps useful with one form of the equation for depth of field!)
However, just in front of the aperture ring there is a curious lever, which moves through a slot, with a travel of almost exactly 90 degrees. It moves a ring inside the lens that doesn't seem to do anything.
Ny first thought was that it was a reminder of the aperture you planned to use, to facilitate resetting it after opening up fully to focus, but its travel doesn't seem to match that.
The ring inside has a somewhat curious exterior profile, but that might be the result of breakage. It is split at the point the little lever is attached by a screw. (As a result, when you pull the lever, it spreads the ring and prevents it from rotating). It looks as if it has a recess on its front side that could receive some circular plate.
It is almost as if this is intended to rotate an internal polarizer, although that seems far-fetched.
Does anyone know the purpose of this lever and ring?
Thanks.
Best regards,
Doug
The aperture ring is conventional, but it has a second scale, calibrated in mm, which seems to give the exit pupil diameter! (Perhaps useful with one form of the equation for depth of field!)
However, just in front of the aperture ring there is a curious lever, which moves through a slot, with a travel of almost exactly 90 degrees. It moves a ring inside the lens that doesn't seem to do anything.
Ny first thought was that it was a reminder of the aperture you planned to use, to facilitate resetting it after opening up fully to focus, but its travel doesn't seem to match that.
The ring inside has a somewhat curious exterior profile, but that might be the result of breakage. It is split at the point the little lever is attached by a screw. (As a result, when you pull the lever, it spreads the ring and prevents it from rotating). It looks as if it has a recess on its front side that could receive some circular plate.
It is almost as if this is intended to rotate an internal polarizer, although that seems far-fetched.
Does anyone know the purpose of this lever and ring?
Thanks.
Best regards,
Doug