Adapter for Mitchell (also B&H2709, Newall & some Baltar and Astro Berlin etc) lenses in the 1920-40s News Camera mount to NEX or Micro four thirds.
The printed adapter is to a 52mm 0.75 pitch thread, as used on some reverse lens adapters. The length of the adapter (23.8mm) was chosen to suit the flange distance for micro four thirds, once the part is attached to a suitable reverse lens attachment. In practice, the lens is likely to slightly read 'under distance' and focus past infinity, but most helicoid designs of this vintage allow for physically adjusting the infinity marker position, if this is prefered.
If a reverse lens attachment for NEX is used then the distance marks on the lens will be slightly further out (but will still focus to infinity). Either a 0.7mm shim or rotating* the distance ring on the lens to reset the marks will correct this. (* All of the mitchell lenses I've adapted have this adjustment, but it would need to be changed each time the lens is moved between NEX or M43 (or a B&H 2709 / Mitchell if you have one!)).
Two sets of mounting holes are provided for, as there are two styles of mounting (sometimes external to the lens and sometimes hidden on a smaller diameter circle of holes).
As well as the 3D print, 4 off M3 screws and the appropriate reversing ring is required (these are $2 or $3 on ebay). You have to be very careful to avoid cross threading the first time a reversing ring is fitted (it may be easier to line it up if you attach the reversing ring to a camera first).
Aside: Mitchell lenses with only 3 screw holes are for the Mitchell 16mm mount, the flange distance for this is too short to adapt to either NEX or M43.
I've found the nylon prints quite strong enough for my lenses, so I havn't tried in stainless steel. That would be at your risk, though the cost (around $80) would justify printing with a fixed M43 or E-mount, camera side rather than the reversing ring, I will consider making a version for this.
see also the Allstar intermediary mount to NC.