|Posted: Sat Aug 16, 2008 5:53 pm Post subject:
This looks like the machinist cut the back (with the lens mount) off the Biotar rear tube, as it is one piece, and put on a machined sleeve over the remaining tube held on by screws.
Shortening the tube this way gives an easy adjustment for the deeper Nikon mount.
A very neat and professional job, if rather drastic. I don't know if this reduces the collectible value of the Biotar. Odds are, at the moment, probably not, but at some time in the future it may be a different story.
I was thinking of a similar but much less destructive adaptation to PK, with a machined T-adapter fitting over the back of the rear tube and preserving the Exakta-mount, and held on by set-screws. There is enough extra depth in the helical mechanism to adjust for both the difference in mount depth plus the thickness at the bottom of the T-adapter, the only functional compromise being that the focusing scale is off.
The only loss here would be damage to the barrel from the set-screws, or possibly the need to drill some dimples for the set-screws (a neater solution). A good machinist could do a very neat job of this also.
Fortunately, it is in fact possible to make a completely non-destructive Biotar adapter for PK, and I believe this may be possible for Nikon also, if one accepts that the focusing scale will be off.
I like Pentax DSLR's, Exaktas, M42 bodies of all kinds, strange and cheap Japanese lenses, and am dabbling in medium format/Speed Graphic work.