Originally posted by JohnX What did you do immediately before the spring came loose?
I had just unscrewed a "clamping plate) (on the left in the first photo attached) and then removed a short "tube" (on the right in the first photo attached and by itself in the second photo attached).
To be clear:
-When I first obtained the lens, and when it was not mounted on the Pentax camera, the aperture control "tab" would stop down the iris diaphragm when I pressed it but when the tab was released the diaphragm was "sticky" i.e. reluctant to open again.
-When I started to investigate the problem I unscrewed three tiny screws on the clamping plate, removed the clamping plate, then removed the short tube (both shown in the attached photos).
As the spring has a loop at its end it must loop over a pin or tab somewhere in the barrel of the lens. Its function, if I understand it correctly, is to stop down the diaphragm at the moment of exposure. that means that the spring must somehow be connected to the diaphragm but at present I cannot see how that connection can be made. I have tried looping the spring over a couple of features on the short barrel thing but that somehow is very tricky and doesn't seem logical.