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SMC Pentax M 50mm lens fix (page 2)

6 You are now left with this. The silver ring is supposed to turn in the black ring, mine didn't. I have not seen these pieces disassembled, but I have the impression that protruding circles in one piece fit into grooves in the other to allow the necessary turning while holding them in their relative positions. When the lens is dropped the 2 rings are no longer aligned, or the grooves and protruding circles are no longer properly engaged and the focusing is jammed.


7On the "A" lens I was able to use a screw driver to pry the silver ring out a bit and it snapped into its proper position and started turning properly. The "M" seemed to be pushes so far back that there was no room for prying. So cut 2 notches on opposite sides of the back side of the black plastic piece (see picture on the right), cut a circular hole in a board that was bigger than the silver ring and smaller than the black one, placed the piece front down on the hole and used a hammer and a screwdriver to tap on the silver ring to move it out a bit. With a bit of tapping and fiddling about I was able to free up the mechanism.
Unfortunately that was not the end of it, when I tried to reassemble the lens I found that I had gone too far and I had to squeeze the silver ring back in a bit (I used a vise, gently). It took me 3 tries before I could reassemble properly.

8 Now it's time to put it back together. Screw the lens elements unit in so it sticks out slightly in the back, then align the grooves at 5 o'clock and 7 o'clock to replace the copper coloured tabs. The slot that gives access to the aperture has to be at 2 o'clock. The groove at 12 o'clock is not used. (how would one explain this in a world with only digital timepieces?). Install the piece that has the tabs that activate the aperture with its 3 screws.

 

9 Putting the aperture control ring back on is tricky because of that little metal ball mentioned in step 5. Make sure the spring is in the hole, I used a dab of grease to hold the ball in place. Then place the control ring on the ball from the top to hold it in place while you complete the installation of the control ring. If you don't do it right the ball slips off its spring and lodges in the second hole just in front (My "A" lens didn't have this second hole). I used a magnet to remove it from this embarrassing situation (see picture below). Be careful that the control ring does not slip out of position during the next step, or else you will have to repeat the above.

10 The washer with the dimple can now be placed, make sure the dimple is between the rear lens housing and the actuating arm that moves the aperture tabs, not sitting on top of it. Before replacing the K mount move the aperture control ring to f22 and place that dimpled washer so that there is space between it and the lens housing, a lip on the K mount fits in here. On the "A" lens you have to make sure the contact mentioned in step 4 is in place (I haven't figured out how to do this, I reassembled without the contact to allow me to test the lens). After having placed the K mount, before screwing it down, move the aperture tab that sticks out of it to make sure that the aperture blades move freely, if not the lip on the mount is touching the dimpled washer - wiggling things around seems to get everything properly seated and you can screw the mount down.