tamron 2x t/conv bbar mc f system

Tamron tele-converter 2x bbar mc for pentax-k f system.(Thats whats on the lens) Just bought this from a little camera shop in Hertford. Don't know anything about it, just that it was in great nick, original caps and original leather case also in great condition(mint). As it had f system on it and I have several f series lenses I thought why not, only a tenner. Anyone know anything about this particular model? I won't be home til tomorrow so can't try it on camera.

It's not bad, in my experience one of the better low cost 2x teleconverters. I once compared a handful of these sub-£20 TCs and this one and the Vivitar/Kenko 2x macro focussing TC were the best of the bunch. The others I looked at included a Takumar-A 2x, Adaptall-2 2x and a generic Vivitar 2x. Nothing terribly scientific, just some brick wall shots and my own eyes. I ended up keeping the Kenko for the macro ability plus it has PKA contacts which my Tamron-F didn't.

Do note however that 2x TCs in general will noticeably degrade your image quality, no matter how good they are. Avoid using it on budget lenses

Thanks Tim, I know nothing about t/c's in general although I have a macro version of the Vivitar which works great with my 50mm A. I just bought this one because it was in virtual mint condition and seemed very cheap at a tenner. Regards, Ben.