Originally posted by MattGunn .....The latest conversion is a Vivitar 55mm f/2.8 macro, originally in Konica AR mount. I know that this lens is available in K mount but I got it so cheep that I though it was worth a try in spite of the potential difficulties of acheiving infinity focus from a mount with a registration distance 4.8mm shorter than K mount.
The conversion involved dismantling the lens, removing about 4mm of metal from the back of the lens mount and the aperture ring, machining a new recess into the back for bits of the aperture mechanism, drilling and tapping new holes and fitting a flanged M42 adapter. So that I didn't have to stop the lens down before taking a picture I made and fitted a new aperture actuating lever so the lens workes as an M lens as the original K mount version did. It also reaches infinity focus.
As with previous conversions, I had a go at making it an A lens as can be seen from the photo. Unlike most of the previous lenses, in this one the aperture mechanism provides a linear change in aperture area with lever movement so I was hopefull it would be more sucessfull than previous attempts. However the aperture lever movement of the K AR lenses is greater that K mount. At the wide end it was OK but at the smallest aperture the exposure was almost 3 stops too high so I took the A pin out again and now just use it as am M lens. I haven't tested it much yet but it is another impressively sharp lens. A photo of the converted mount is shown bellow.
One thing I have noticed in converting vivitar and Kiron lenses from Minolta or nikon to PK mount is that you don;t have to remove any metal at all.
THe vivitars made by Kiron, and the Kiron lenses I have modified have a very long focusing helix. In fact I believe they did this as the means of accounting for all the lens makers in the main mechanical design.
THe focusing ring is attached to the helix by three screws visible when you take off the cosmetic collar at the front of the lens.
There is a small set screw and the collar threads off whe this set screw is backed out a little.
You can see past the fllange a at the front the 3 screws and large washers.
Just losten these off and you can modify the infinity focus point to suit the new mount distance as the focus limits are only based upon the focusing collar.
I will try to attach a few shots later or perhaps a sketch.
But I now have 2 fast wide angles, a 24mmF2.0 Vivitar by Kiron, with Nikon AI mount, and a 28mm F2.0 Kiron for Minolta MD mount, and both focus just fine to infinity after mounting flanged K mount M42 adaptors