I know there are lots of websites and blogs that show you how to convert various lenses to various DSLRs. Here are some pictures of my conversion. The flange-to-film/sensor distance on the MC Rokkor is 43.5mm and the EOS is 44mm so basically you need to remove enough of the old lens mechanism to offset the thickness of the adapter that you are using. I used the cheapest Hong Kong M42 to EOS adapter I could find in brass. I've since used alloy adapters and they work just as well and are a bit lighter.
1. Start removing the tiny screws from the back of the lens.
2. Keep removing things that are outside of the aperture ring (the ring that says 1.7 2 2.8 etc...)
3. Before you remove the aperture ring, make sure you keep the ball bearing and spring that makes it "click" from one aperture setting to the next.
4. At this point, you can re-work the spring mechanism. I just cut and bent a ballpoint pen spring to fit between the brass aperture mechanism and a nearby post. I can't remember why I didn't use the original spring. Maybe it was too long or too short or something else.
5. Measure your adapter thickness and see where that lines up with the various layers that you have removed. If you are lucky, you can just use one of the things you took off.
6. I wanted to use the original screws so I sanded down the silver spacer next to the aperture ring and put it back on.
7. I used the holes in the spacer as a template and drilled 2mm holes in the adapter.
8. I then turned the adapter over and drilled 4mm holes on the other side.
9. The aperture ring has a single inward facing "tab" that goes between the two vertical "prongs" of the aperture mechanism. As you focus, the tab moves up and down the "prongs." Depending on your adapter, you might need to clip the tops of the prongs so they don't hit the adapter. I clipped mine too far and had to solder a wire on top of my prongs to get the height back.
10. Put the screws back in and see what happens. If you try to focus and cannot quite get infinity to focus, you need to sand a bit off the spacer or the adapter and try again. If you were a bit too enthustiastic with your sanding, and you can focus "past" infinity, you might want to add a sliver of a spacer.
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