Old manual focus lenses are super cheap, and very compatible with current Pentax digital SLRs.
Because the CMOS sensor in digital SLRs are not as larger as a 35mm film cell, you end up with the lens delivering 1.5x the focal length it would on a film camera, which is kind of nice on a telephoto lens, but a hassle with wide angle.
Anyway, some old Vivitar lenses won’t fit on new Pentax digitals, the little guard for the aperture pin is too wide. I got myself a very cheap ($20!) Vivitar 70-210mm zoom off ebay, and needed to trim down the guard so it would fit.
I am going to cut the guard back to just after it reaches its full height.
2) Remove the two *tiny* screws that hold the ring in place. Don’t lose them!
You might want to do this in an environment less dusty than my workshop, but I like to live dangerously.
3) Clamp the ring securely in a vise. Be careful, the metal is quite brittle and more likely to snap than bend.
4) Carefully saw away the superfluous guard metal. I found the waste piece easily snapped off when the cut was long enough. It is necessary to support the ring while you are sawing – I held it firmly with my fingers next to where the blade was cutting. I also only used the draw stroke so the cutting was more gentle.
5) Re-attach the ring. You can see the silver arc where the guard was cut away. I was intending to file the rough edge, but it is not too bad, so didn’t bother. Now would be the time to find the screws you lost earlier.
7) All done. Here are some snaps showing the zoom range:
For more details on using manual lenses with Pentax digital SLRs see here.