[ripit]

How can I tell a sigma mount auto focus lens from a k mount lens? based on pictures it looks like the electrical contacts are in the center like a canon lens on sigma mount but I have been unable to confirm it? Is there an obvious way to tell them apart?

[Adam]

Here are photos of the K mount, which should make it easier for you to compare the two:
https://www.pentaxforums.com/forums/pentax-lens-articles/87589-photos-k-m42-m...-k-mounts.html

[ripit]

Thanks. I actually have lots of pentax and 1 m42 lens but I can not confirm for sure what the sigma auto focus mount looks like. From what I have found the bayonet is very close to the same so I'm trying to find where the contacts are on sigma. I found one picture and thew contacts for sigma were in the center ring like a canon lens, not on the flange. I couldn't confirm for sure it was in fact a sigma mount though. The lens I want has contacts on the flange.

[newarts]

Sigma SA mount - Wikipedia, the free encyclopedia

The SA mount uses a bayonet mount which is physically similar to the Pentax K mount[1] but uses a flange focal distance of 44 mm, identical to that of the Canon EF lens mount. The mount uses electrical communication between body and lens, like the EF mount, and in fact uses the same signalling lines and protocol as the EF mount, despite the physical incompatibility. Sigma has long produced EF-mount lenses for Canon cameras, and thus had the ability to use this protocol. ............
Pentax K mount (PK) lenses can be fitted straight onto the SA mount, after the protruding AA lever and AA protector outcrop are removed, though the fit is slightly loose as the SA mount has a slightly bigger bore than the PK mount.

[ripit]

I found a wiring diagram in google images that showed the contacts in the center ring so I think the lens is pentax (contacts on the flange). Thanks for the help everybody.