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10-19-2011, 04:29 PM   #61
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I'd like to see a Minolta MD mount mod.. I've got an adaptall2 to MD mount and one other minolta MD mount lens, as well as a friend who has 3 that are unused and collecting dust...
you should setup a picture filled blog or post of your mods and which work best, which just "sorta" work etc.. it would definitely help expand the rest of our LBA!

10-20-2011, 04:44 AM   #62
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One thing I should note is all the ones I have done have not been minolta or canon brand. As I understand it, aftermarket lens makers just design one lens, then adapt it to the different mounts so they are already set up to work with most mounts (without having to cut back anything on the lens itself). Basically, unscrew the old mount, screw on the new mount, use a spacer to push the mount further away from the lens if necessary. Use a second spacer to hold the aperture ring down .
look at the picture in my posts towards the end of page 10 and the beginning of page 11, then read this, then read the rest of the other thread from the beginning.

https://www.pentaxforums.com/forums/lens-clubs/64271-impossible-lens-club-10.html

Page 10 is a donor mount with a 52-49mm step ring for a mount spacer, and a white plastic ring (from the bottom of a filter case) for an aperture ring spacer (I know the white plastic is ugly but it works and one of these years I'll make a proper one).

Page 11 is an m42 adapter and the spacer rings were parts gutted out of a canon lens if I recall right (using a macro-pk adapter would be similar).
Your mount can either be one stolen of a junk pentax lens, or an adapter. Be aware, using this simple form of conversion, you will most likely either have wide open only aperture, or you will have aperture control similar to an m42 lens (you turn the aperture ring and the aperture closes down, you turn it the other way and it opens up, and thats it, no camera control of the aperture). It just depends on the lens which you will get. Take the mount off the lens and see if the aperture ring still works to see. You could of course modify it further to get more control but that would involve a more complex procedure including making/modifying parts. If I'm not mistaken, some have modified lenses to have full function. I have one lens setup where I can finish it later and possibly get full function (right now it has m42 type operation).

For the mount. first option, you can use a donor mount off a junk pentax mount lens. Ideally find one with the same hole spacing for the screws. Many aftermarket lenses have extra screw holes on the lens so that the lens can fit different mounts so even if they don't match, it may work if your donor mount holes line up with the available holes on the lens (regardless of what holes the original minolta mount used).

Alternatively, use an adapter. When I first started, many recommended an m42-pk adapter. I strongly recommend against that!!!! You have to counter sink for the screw heads. One of the lenses I did had screw heads that were .035" thick with a flat bottom edge. An m42 adapter is only .040" thick. You are going to have to make a precision counter sink and only be left with .005" or less holding the lens on. I wound up doing a combination of bending and cutting the counter sink in on an m42 adapter to get deep enough. It was a giant nightmare that took a couple of hours. I wound up punching right through the mount trying to bend it so I had to move to another position and try again. Obviously a screw with a thinner head and or one with a tapered head where you can do a tapered countersink might work better with an m42 adapter. A pk-macro adapter is about .080" thick and seems to work just as well. It is easy to cut a .035" counter sink into something .080" thick with .045" left instead of .005". Again, it depends on the screw heads how much issue an m42 adapter will be.

Important!!!!!!! You will want to use the original screws (I would assume since they fit the lens). Your new mount will be much thinner than the minolta mount. With every minolta lens I did, I had to shorten the screws. The first time, I almost thinned the mount spacer too much not realizing the screws were bottoming out and not tightening the mount down all the way. I used the original mount as a template to drill holes through the adapter. You will most likely need a spacer between the lens and the mount.

Minolta sr mount is 43.5mm. Pentax is 45.46mm. Measure the original minolta mount. The new mount must be about 2mm thinner. Adapters will probably be much thinner hence the need for a spacer. Be aware the original mount may likely have an outer ring that held the aperture ring down. You need to measure inside this (or measure the whole thing and subtract the height of the ledge). If the new mount is too thick, it will not focus to infinity (thats a problem). If the new mount is too thin, it will focus past infinity (not a problem), and you will loose some of your macro range (not a problem unless its way too thin and or its a lens you want to use for macro).

I think that is most of it but to be continued as I worked and overnight, and have not slept yet. Good night.
10-20-2011, 01:46 PM   #63
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The spacer ring for the mount (the inner ring) need to be pretty precision as it is what holds the mount to the lens. It should be the same thickness all the way around. You will probably need to drill/cut clearance for the screws. The outer ring that holds down the aperture ring doesn't need to be precision at all, it fact it needs to be a little loose so the aperture ring can turn freely. I have used step rings (in fact you can see the 52-49mm step down ring behind the mount in one of my photos) and or rings stolen from parts lenses. I guess whatever kind of metal (or strong, hard plastic) ring you can find.

I'm not sure what else to add. Hopefully it wasn't too confusing as I was half asleep when I wrote it. I really would like to write something out with pictures documenting some of my conversions but working full time with 2 small kids and other issues, free time seems to be little (I actually have several lenses waiting around to be converted but haven't had the time).

Any questions?
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