sorted thanks

[wack61]

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[CT]

I'm pretty sure, it's the Pentax K bayonet, which Pentax introduced when they swapped from their previous screw mounting system. Sigma and several other manufacturers also used the Pentax K bayonet on their camera bodies as it was a popular system

In it's simplest, earliest form it was just a 3 prong bayonet with no electrical connections. However, as time passed more and more electrical connections were added to the mount as the degree of auto coupling between camera and lens increased, and electronics in the camera increased with auto focus etc, being added.

Can't help more than that I'm afraid, but have a read of this which may be of some help.

CLICK

 

[wack61]

Thanks for that, looks like it's headed back to ebay, do the current line of Sigma/pentax DSLRs still use this fitting, it's a 70-300mm sigma so hopefully I can sell it on

 

[Slipper-one]

It's a Pentax. Sigma use the same/similar bayonet but the electrical contacts are different and no actuator(?) left side.

 

[silverJON]

Thanks for that, looks like it's headed back to ebay, do the current line of Sigma/pentax DSLRs still use this fitting, it's a 70-300mm sigma so hopefully I can sell it on

Yep - autofocus, and perfectly compatible with all new Pentax and Samsung DSLRs.

 

[wack61]

Brilliant, thanks very much to all that took the time to reply