m42 screw thread ,confused

[the black fox]

just been given a eos to m42 chipped convertor ,now looking through available m42 lenses on e/bay i have noticed that some are just a screw thread ,while some have a small protruding pin on the end ,which once the lens is screwed into the mount will still protrude into the camera throat ??? so the question is will this cause a problem or is it safe to fit to a canon camera

 

[BacktotheFuji]

The pin is used to close the aperture blades once the shutter is released, and is found on 'auto' m42 lenses. Some have a manual switch which keeps the pin inside the lens mount.

Anyway, the pin won't damage your camera, they are not long enough. Most M42 to Canon adapters have a flange to keep the pin pushed in anyway. If your adapter doesn't have this feature, then you will need to look for either fully manual (preset) lenses or auto lenses with a manual switch. Alternatively you could glue the pin down. If you don't do any of these things, and don't own a flanged adapter, you will only be able to shoot auto m42 lenses wide open.

 

[the black fox]

Cheers I think I have just realised that myself ,my lad gave me two adaptors the chipped one is just a screw thread ,the unchipped one has a flange at the bottom of the screw thread .this is I believe exactly what your talking about and it all makes sense now .
Just got to find a lens to play with now