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This fits the following lenses in Arri Std mount,
Taylor Hobson Panchros, 35mm & 50mm (Mk1)
Taylor Hobson Kinetal 12.5mm (both versions of this lens, sn 59.. & sn76.. ), 17.5mm.
possibly others with a focus ring, 51-52mm diameter.
The gear is 85mm dia. & pitch .8
The part has been sucessfully printed in PLA & ABS
It may be less than ideal fit for some of the other versions. It's best to contact me if you are not sure or want a slightly different design.
It is a two part piece , and uses 3 off M2.5 x14mm* screw/bolt and nuts to clamp it firmly to the focus ring (If you can't source these, I'll send them for the cost of postage). It is prevented from slipping by using the existing "focus ears" screws. It was designed to be used in conjunction with various lens adapters, eg the Arri Std to PL adapters, where the lens is set into the throat of the adapter... hence the gears are set forward of the piece to easily clear the camera. (Suitable 80mm fronts are also avaliable if required for your matte box).
(* screws: ~13-16mm long will work OK, lock-nuts require 14mm screws or longer)
Cons: the gear wraps over the aperture ring (especially on the 12.5 Kinetal) so it is a tight space in which to change aperture.