Sorry yes you are right, the iris closes when its removed from the camera so the spring holds it closed.
I hope you dont think I was being bolshy there.....promise I wasnt I was just trying to explain why the FD adaptor is awkward. Ther is much stuff online saying its completely backward and forward compatible and for OM and PK thats true enough but for the FD, and I suspect the Konica mount, where the adaptor seems very complex, they arent.
Its a massive pain because whenever I have bagged off an AD1 lens I am stuck trying to find an original AD1 adaptor which for the FD type means a specific aperture as well.
Lucky for me so far I have bagged them easily but some seem harder to find like the 2.8 one. Its worth bearing in mind for anyone with an FD camera.
Oh also I have read there were two types of OM adaptors as well. The OM amd the OL. The OM4 demands the OL type.
I am not a particular fan of Tamron but I now have so many bodies PK, OM, FD, Nikon pre AI lobster claws and AI the Adaptall stuff has a certain sense plus OEM kit has gotten mad on prices of late especially Pentax and Olympus.....Nikon always was so no change there.
I have no love for Canon FD glass unless its the early types, the later nFDs are impossible, look horrid and completely unrepairable in most cases thanks to glue and cheap and nasty construction.
---------- Post added 08-21-19 at 10:18 AM ----------
Oh ps I should have mentioned when the AD2 adaptors are mated to an AD1 lens the aperture will stop down...it just wont stop down all the way so if you are shooting wide open you wont see a proble, it may stop down to the halfway mark so if the lens has a midpount at f8 that might work as well but it sure wont stop down to say f11 or f16 or whatever the smallest aperture may be and its may be very erratic at all settings. My FTb will make all of them stop down to about 3/4 of the way through the range but the AE1 is super erratic and all over the place.