I am betting that you unscrewed the focusing helix. Large aluminum threads, greased? There should be a warning label, don't unscrew this. The large threads have (I think) three starting points. It takes a lot of patience to get the right one. When you have the wrong entry point, the rest of the parts don't line up in the right place.
The main reason for doing that is, your M50/2 doesn't focus any more. A drop or whack causes focus to stick. Often someone strong tries to force it, and the grip peels off too. Lots of these jammed lenses on eBay. The problem is not that obvious, and you may not have fixed it yet. You have to start at the front. Unscrew the trim ring with the lettering on it, or if the filter threads were damaged in the accident, pop it off; it's plastic and has little slots in it 180 degrees apart. If you unscrew the three screws holding the brass washer, you can remove the front lens group entirely. There are three more screws holding the focus ring on. Remove those and take off the focus ring. Your lens should look kind of like the last photo except that's an M50/1.7. The aluminum ring here is the jammed part. It will be tilted off axis, so the ring is not parallel to the parts underneath it. You have to pop it back onto its fine threads. I just look for the low side and pry it back up.
Once that ring turns properly, you can reinstall the focus helix. First screw that aluminum ring all the way tight, then loosen it about 10-15 degrees. In the third photo here, the lens on the right is almost stripped down. One L-shaped copper piece has been removed here. It's called a guide bar, and it keeps the lens moving in and out, not turning as you focus. What I did was remove both guide bars, screw in the focus helix, and see if everything lined up right. That meant reassembling the stuff on the back of the lens. If everything goes on right, you win, and can put together the front. Or try again, trying to rotate the helix 120 degrees each time to get it to start in a new place.
You'll have to reset infinity focus when you get the lens nearly back together. Once you have the mount and back end on, put the front lens group back on. Tighten the aluminum ring again, and back off the same 10-15 degrees. Put the focus ring on with only one screw tight and the orange diamond somewhere close to infinity. Now put the lens on a camera, point at something infinitely far away, and focus until it's clear. Once you get sharp focus on a distant object, loosen the tight screw, rotate the focus ring until the diamond points at the infinity symbol, then tighten all three screws. Put the rest of the lens back together.
These photos are about 5 years old, the last time I did this, so I might be missing something. Filter ring, I skipped that. Anyway, they should show just about everything in an assembled or unassembled state.
Last edited by Just1MoreDave; 07-28-2011 at 02:42 PM.
Similar Threads 
