Minolta MC Rokkor 58mm f/1.2 mount conversion, part 1/5

Guide to converting the lens mount, introduction



Here is the new Minolta AF lens mount attached to the old Minolta MC lens. The lens mount itself is actually a cheap M42 to Minolta AF adapter, which is a cheap way of attaining the Minolta AF mount. You can use an M42 to Canon or a thin glassless M42 to Nikon adapter just as well, depending on the camera system you use. For Pentax K-mount you'd need to find an adapter which has the "lip" outside the lens mount. You cannot easily convert this lens to M42 mount, since the rear element is almost as large as the mount's minimum inner diameter.


This series of photos is a brief guide to how I converted mine; required parts are the original lens and the M42 to Minolta AF adapter. The conversion is reversible if you retain the original parts, but the reversal requires almost as much work as the conversion.


This guide displays the disassembly of the completed modification, but the disassembly is mostly the same for the unmodified lens. Reassembly is simply the same in reverse.



Disassembly: Mount


On an unmodified lens, instead of the black adapter seen here, there will be the original Minolta MC lens mount, attached with eight screws. Four long screws go through the mount spacer, and four short ones hold parts of the mount together. You can just remove the long ones to disassemble the entire mount (to find out which are which, remove any one screw... if it's long, the screws next to it are short, and vice versa). This is safer for things like adjusting infinity focus or cleaning the aperture blades, as a lot of tiny ball-bearings can fall out if you carelessly remove the aperture link ring (right under the original MC mount).


The long screws will be used to attach the new mount. The short ones will be simply removed in order to free the mount spacer ring. After opening all of the screws, carefully lift off the original mount and the aperture link ring. They are the two topmost rings that will come off. Do this so that if you accidentally cause tiny ball-bearings to fly, they will land somewhere where they won't get lost. They aren't needed for the modified lens, but it's nice to have a reversible modification.


See the next picture for more. This series of pictures was taken with a Minolta 50mm f/1.7.

  • Kimmo Kulovesi 7y

    mardy78: With my lens and adapter there's about 0.3 mm of clearance between the adapter and the lug on the aperture ring, so I left it alone. But, yes, it's useless. =)

    For the spacer I suggest aluminium baking foil instead of paper. Fold it a few times to make about 16 layers, then cut the shape out of all layers at once and put as many as you need. Worked great for me; it's easy to remove one thin layer at a time until exact focus is achieved.

    As for other MC/MD lenses, I don't have any experience converting them. I had a 135mm f/2.8 lens, but it was broken, so I didn't try to convert it, but I noticed that it would have been harder to convert with the one-piece aperture + mount.
  • tommycaliu 6y

    Hi Arkku: thanks for the walk through. recently I got a Minolta MC Rokkor-X 135MM F2.8 lens. thought it's the one you mentioned "harder to convert" one. when I tried to take old mount away, noticed something connect to deep, don't know how to take it out, any advise?
  • Kimmo Kulovesi 6y

    tommycaliu: Some other Rokkors do indeed have the aperture mechanism and the mount as a single piece. To modify them, I suppose you would have to cut of the mount somehow while leaving the aperture mechanism intact. I don't have such a lens currently, so I'm not certain of how it might work.
  • Henk Rijks 6y

    Hi Arku, thanks for the great work you did. Do you know if there are any snap-on adapters available to mount a Rokkor 58 to a Sony Alpha without having to tinker with its mechanically? I am not as handy as you, and I'm recluctant to do something irreverible to my Rokkor. ;-)

    Thanks in advance,

  • Kimmo Kulovesi 6y

    Powerpop: It's physically impossible to devise a “snap-on” adapter which both retains infinity focus capability and does not include image-degrading (and focal-length altering) glass elements. That said, many people have had good results with the adapters despite the limitations. For more on these, see this FAQ (search for "Rokkor").

    If you mean an adapter specifically for this lens, I believe Pete Ganzel might make one. However, it's bound to cost more than this conversion and still requires you to disassemble the old mount on the lens. If you happen to have the exact same model of Rokkor as I do, I'd still suggest braving the conversion; it's not really that difficult, and you can always ask for help if you don't know how to proceed. (If you have another model of Rokkor, then it's more risky because I don't know if they disassemble the same way as this one.)
  • Henk Rijks 6y

    Arku, thanks again. I might as well jump in then... My Rokkor is identical to the one you used. Fact is, I inherited a whole bunch of older Minolta lenses, and I was hoping for a one size fits all solution.
  • Napolitan_2000 6y

    "You cannot convert this lens to M42 mount, since the rear element won't fit inside."

    Ummm really? I know you can the 50mm .. I know many people that have .... Do you wanna see pictures? I should email this camera shop that does alot of lens conversions and ask them about the 58mm.

  • Kimmo Kulovesi 6y

    Napolitan_2000: Yes, actually I've heard of 58mm to M42 conversions with custom parts since I wrote the above, e.g. I think Pete Ganzel said he'd switched to making M42 mounts for this instead of Minolta AF.

    However, the diameter of the rear element (including the retaining ring around it) is slightly over 38mm on this lens while the smallest outder diameter of an M42 mount measures approx. 41mm. So, with simple DIY parts (e.g. mount salvaged from an actual M42 mount lens and no lathe available) I'd say it's practically impossible due to very tight clearances and resulting thin sides of the mount itself. But if you have good materials for the new mount, and access to a lathe, then by all means.
  • aurelienbrentraus 5y

    i have minolta md 50mmf1.4, 28mm f2.8 and 28-90 mm f2.8 lens
    and i have AF alpha mount sigma lenses as well, but i want to know , can i change the mount of alpha to canon or nikon, or minolta md mount to canon or nikon.

    i want to make use of these lenses.please advise me how to do it.

    i want to change the mount of lenses . please help me how to do it.
  • Kimmo Kulovesi 5y

    aurelienbrentraus: You can't change the mount on the AF lenses because there is no manual aperture control.

    You may be able to convert your MD lenses to Canon or Nikon mount following similar steps as I've presented in this guide. Each lens is different, however, and most likely you will need to rig something to gain aperture control after conversion.
  • Eric n6oim 5y

    If you (or anyone else) has the actual part number for the "thin glassless M42 to Nikon adapter" it would be greatly appreciated to learn what it is. When shopping for the M42 to Nikon adapter, I'm not seeing any that state "Glassless" but there are several others to choose from. I know the thickness tolerance is a big factor, and wanted to make make sure I'm purchasing the correct one. Thanks!!!
  • Kimmo Kulovesi 5y

    etgeek: Just go on eBay, type in “Nikon M42 adapter” and pick one that's cheap and has no glass and looks no thicker than the black adapter seen in this photo. Plenty of suitable-looking adapters come up on the first page alone.
  • robert mcluckie 5y

    how do you get the camera to see it as 1.2, as in exif data? I've done the conversion, no focus confirmation, but the camera sees it as 00
  • crazzycol68 4y

    when ive built up my collection a bit more, im going to tinker with a conversion, my question is the adaptor, i see ally one's, same metal used by minolta, either silver or anodised black, then there's brass one's, would the brass one's be stronger than the aluminium ones?? as the constant of and on of the lens wear's the edges down and makes for a sloppy fit
    awesome thread by the way, glad to see people going back to the old stuff
  • Kimmo Kulovesi 4y

    I doubt the adapter's material will make much of a difference here, choose whatever is most convenient and makes you feel better. =)
  • christophergreene 3y

    I have had this conversion for a couple of years now. I attempted today to reverse the modification and I have hit a confusing snag. I left the original mount fully assembled and expected to just screw it back on and begin using the lens with my SRT 101.

    The problem I am having is that the aperture lever in the mount does not reach the round aperture pin in the lens. Am I missing a connecting piece between them? I do not understand why the lever does not reach the pin. The lens mount can only be reassembled one way, as the screw and spring attached to the MD mount have a slot cut for them in the base of the black lens frame.

    Any advice would be greatly appreciated.
  • BOB SMIT 3y

    amazing lens, very odd, but I have the yashinon 50mm 1.9 which is amazingly good also, and I need the m42 adaptor, does the adapter need the flange push pin for aperture pin to push?
  • BOB SMIT 3y

    how can you use also m42 to canon/ nikon?
    Does that work for my alpha 580 sony?
  • Kimmo Kulovesi 3y

    The M42 part is completely irrelevant in this conversion. It could be M45.6789 to Sony and it would work just the same here. The Rokkor 58mm f/1.2 is not an M42 lens, and this conversion will not turn it into one. The M42 adapter is just a cheap source of the Sony/Minolta AF mount. So if you have a Sony camera, do this with an M42 to Sony adapter, if you have a Canon camera, use an M42 to Canon adapter. Again, the M42 part is irrelevant—it just happens to be a mount for which you can buy cheap adapters, but the interesting part is on the other side of the adapter (i.e., the X in “M42 to X adapter”, where X is your camera brand).

    As for the Yashinon question, it's not really related in any way to this conversion but see this FAQ about M42 on Sony. (Short answer: probably, or you can mod the lens.)
  • M L 1y

    Anyone know the sizes of the mount screws? Mine are stripped and i need new ones.

    Thanks, Myke
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Taken on August 29, 2007
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