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Exakta mount conversion to M42.
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PostPosted: Wed Jun 23, 2010 1:04 am    Post subject: Exakta mount conversion to M42. Reply with quote
These are the Primagon 35mm f4.5 and the Biotar 58 T as you can see- both on Exakta mount.


I have had to modify these lens mount after considerable thought, I have shaved the lens mount off the back a smidgen more than a millimeter and used9glued) a m39 to m42 step up adapter around the existing Exakta mount. With the logic that the Exakta register is 44.70mm and the M42 register is 45.46 and shaving off 1mm, and a smidgen gets me to the M42 mount register distance. I did not want to shave anymore off of the lens mount fearing it might ruin the lens-I will be shaving the M42 to Sony AF to correct it more if need be.



I am not a machinist so I had to ask a friend to shave it off on his lathe.



PostPosted: Wed Jun 23, 2010 1:22 am    Post subject: Reply with quote
Looks very neat.

As long as you are shaving the lens, you may want to drill and tap the M39-M42 ring, into the Exakta mount barrel with a deep countersink to leave the M42 thread free, and screw the ring in place. That would be more secure.


PostPosted: Wed Jun 23, 2010 1:59 am    Post subject: Reply with quote
luisalegria wrote:
Looks very neat.

As long as you are shaving the lens, you may want to drill and tap the M39-M42 ring, into the Exakta mount barrel with a deep countersink to leave the M42 thread free, and screw the ring in place. That would be more secure.


Thank you luisalegria, I like your idea and will do this on some longer lenses I plan on modifying in the future.I have been very impressed reading your mount modifications, and your knowledge-you're like a lens library.
On these lenses I have used 2 part quick setting epoxy and they are rock solid-plus the lenses are not bulky and heavy.
I have a Jena Sonnar 135mm f4 with the diaphragm arm-that I plan on modifying in the near future. My plan on that was to disengage the auto diaphragm making it manual and removing the arm(may have to cut it off). Then I planned on shaving that portion down a MM and little . I then planned on using a Tmount to Minolta Af adapter just the outer part. I would have to shave the TMount down a little to fit over the Exakta-covering up the hole that the diapragm arm leaves and also correcting the register distance to Minolta/Sony AF. I could then line up the focusing ring and dot to a comfortable orientation on the TMount ,and either set screw it in or screw it in. Nothing is concrete I just felt like this was a good way to go on the Jena Sonnar 135mm f4. I know its a lot crammed in one paragraph- I hope it makes sense.

Regards
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