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(v1.2) This was designed to replace the Exacta mount on a Meyer Gorlitz Oreston f1.8/50mm lens for a Nikon mount.
The parts comprise a new aperture actuation arm and a threaded ring to replace the Exacta bayonet.
This ring will then fit a 49mm reversing ring to Nikon mount (easily available on e-bay).
The threaded ring is thinner than the original mount and together with the reversing ring the correct distance for infinity focus is maintained as closely possible -some variation in thickness of the print and reversing ring being allowed for, and erring on focusing past infinity.
The reversing ring solution was chosen as a metal lens mount was likely to be more robust than a printed mount (whereas the plastic 49mm thread has proved reliable in other prints, and it doesn't have to be removed).
The reversing ring can also be replaced with other mounts (at the expense of flange depth; other reversing rings are likely to give a shorter length to the lens than is required to keep the distance marks correct, though infinity may still be achievable, close focus will be compromised). Very short flange depth mounts like M43 or Sony E-mount are best adapted via thier own Nikon adapters plus this conversion kit, though a reversing ring and extension tube would also work.
The only downside to the design is the new aperture arm works in reverse of the original such that fully open is around the f16 mark, and fully closed at the f2 end ! It does however rely on a much simpler mechanical arrangement, without the need for springs and leavers. Modern DSLRs won't have an issue with that as you can immediately see the result of aperture and exposure in the viewfinder/screen.
The conversion kit requires no modifications to the lens and is fully reversible.
Remove 3 screws from the rear of the lens & remove the lens mount and attached aperture leaver.
Unscrew the small screw in the side of the lens aperture ring, then screw it back in again and into the hole in the new aperture leaver. (no need to remove the ring).
Fit the new rear ring with the old screws, checking there is no distortion to the plastic ring and thread.
Screw on a Nikon 49mm reversing ring, taking care not to cross thread the join.
The conversion kit may also work on other lenses, eg the M42 50mm f1.8 Oreston, or other focal lengths... but this has not been tested! -Colours and other materials on request.