While just idly toying around today, I made an interesting discovery. A Contax-EOS lens adapter fits around the Minolta lens mount exactly. It is such a good press fit I was able to mount a lens on a camera.
This means you don't have to hollow out the M42 adapter with a lathe to fit over the Minolta mount. I thought this might be a way for conversions with fewer tools.
I think this will make it MUCH easier for some people to do a conversion.
For this test conversion I used nothing more than a Dremel, tin snips, sand paper, a caliper and super glue. You could even skip the Dremel.
Unfortunately there is a limitation. It is best on lenses that have the removable silver ring on the lens mount. Many of the lenses do have this ring. I don't have an unconverted lens with the silver ring at the moment so the photos show no silver ring. See below for lenses without the silver ring.
You still have to do the normal things in a Minolta conversion - cut off the aperture lever and cut off the protrusion on the aperture ring. The Minolta mount will protrude beyond the EOS mount and you will have to file/sand/grind off about 1mm so the mirror on the 5D does not strike it. It is probably not necessary for other bodies.
If you remove 2mm in thickness from the adapter ring as I did in the photos (that is the entire flange plus .5mm), you will have to remove some thickness from the silver ring in order to mount on the camera. You should then be in the ball park for infinity focus. You would fine tune infinity focus with the lens' internal adjustment.
If you only remove 1.5mm from the adapter, just the thickness of the flange, you could use this on any Minolta lens, even those without the silver ring. But, you will have to make up the .5mm somewhere else to get to infinity focus. It may be possible to do that with the with the lens' internal infinity adjustment. But it will mean more work on the lens to get infinity.
They should be available in any hardware or home improvement store. I used the tin snips to cut off the flange of the Contax-EOS adapter to make sanding easier. The brass is soft and easy to cut.
For internal lens infinity adjustment - that varies for each lens. For Minolta you usually have to remove the front name plate and filter assembly. Then there are 3 or 4 screws that lock the grip with the helical. You loosen those and adjust slightly as needed. Then test for infinity and modify again until you get it right.
Adjusting infinity has been discussed here many times for Minolta lenses you should do some searching and reading.
This web site is interesting in that it shows the dis assembly of many Minolta lenses. It is translated from Japanese but you can get the idea. To adjust infinity you would only remove a couple items.
If you have no experience doing modifications, perhaps it is not for you. Everyone makes mistakes in the beginning, but usually on inexpensive lenses. If you are doing a conversion for the first time and it is an expensive lens.... That is not the best combination.
