Originally posted by photolady Yes, that was a really stupid question. I know enough about lenses to know that A setting is locked to it doesn't shift when shooting. And there is something wrong with the lens because using it on my two cameras that are in my sig, this lens when pushing that button and turning the aperture ring, only goes as far as f22, thus shows as underexposed and refuses to move off that, at any aperture or shutter speed setting.
As I said, I knew it was a dumb question, and no offence intended but I generally try to look for simple answers first.
Now to the real problem.
It sounds as if the button itself is defective, as this is what stops the rotation past F22 to the A setting.
The button probably pushes on a leaf spring, or springy metal piece that has a tip on it, that hits a shoulder or bump on the inside of the aperture ring. I suggest a single bump because the tip will hit the bump and prevent rotation to the A position until the button is pushed, and once over the bump you need to push the button to get it back out of A.
If this piece is damaged, or perhaps bent a little from someone trying to force it perhaps the button cannot make contac any more to lift the tip.
If you show a photo of the lens with the mount removed perhaps I can identify which part to either fix, or remove (if you don't care about the A position ebing lockable,