SMC Pentax M 50mm lens fix
Wherein I fix a SMC Pentax -M 1:2 50mm prime lens.
I got this lens on eBay with a Pentax MG (which was good for parts and the disassembly experience only), a flash with the battery gloop seeping out around the battery compartment door (it actually works after having been cleaned up) and a Sears KS Super that was dirty, but in decent shape. But it was the lens that interested me and I was a bit disappointed that the focus was jammed solid. It was also missing the rubber on the focus ring and generally ugly on the outside, although the glass was fine under a layer of dust. Later I bought an SMC Pentax -A 1:2 50mm that had the same problem, having been dropped on its front end (I presume with a K 1000 attached to its rear end) - the repairs were almost identical.
I was never able to find a service manual for the lens, only an exploded drawing of the similar SMC Pentax -A 1:2 50mm that I found on a couple of camera sites. Not having documentation means that I don't have the proper names for the various pieces, I hope that the descriptions are understandable with the aid of the pictures.
The good news is that disassembly and assembly are very easy.
I take no responsibility for what happens if you use these instructions.
1 First to come off is the front decorative ring (The "M" lens has its name on it. The "A" lens is blank) I have a rubber crutch tip that is used as a friction wrench to remove such rings, but in this case the filter ring was in such rough shape that I ended up drilling a couple of little holes in the ring and use my spanner wrench on it.
2 Next remove the three screws that hold the filter ring in place and remove it. There is a copper coloured washer held in place by three other screws that is now visible, do not remove this unless you need to remove the front lens element (which I didn't have to do for my repair).
3 Before doing this step read step 11.
There are 3 small screws that hold the focus ring in place, they catch on a lip around the circumference or the focus ring and hold the ring on (the picture is of the "A" lens which is identical at this point).
4 Now we start in from the rear of the lens, remove the 5 screws and the K mount lifts off. On the "A" lens there is a little contact with a spring that will probably fall out.
5 You can now lift off the odd shaped washer that is part of the aperture mechanism. Note that there is a dimple on this washer that faces the front of the lens (on the bottom in the picture). Now you can remove 3 screws and lift off the piece that has tabs that connect the camera to the aperture. Next the aperture control ring, CAREFUL when you remove it there is a little metal ball that causes the ring to click into its F stops, it will drop out somewhere, there is also a spring that this little ball sits on that you don't want to lose either.
There are now 2 copper coloured tabs, each held by 2 screws that prevent the lens elements from turning when the focus ring is turned, remove them and the lens elements can be unscrewed as a unit.