So after seeing jaeaetee take the lens apart and reading the post
Originally posted by Edzo I do have the same problem with my Pentax DFA 100 mm f/2.8 WR lens especially on apertures f/11 and up (to f/32). I don't have any problems on f/2.8.
I think I have located this problem today to the aperture pin on the lens. When moving it to "aperture open" it will go back very slowly to the small aperture where the pin on other lenses will go back very quickly.
When pushing the aperture pin somewhat to the outside of the lens you will hear a "click" inside the lens and when you let the pin go, it will go back very quickly again.
Is there someone aware of this problem with the DFA 100 mm WR version?
Probably you will have the same issue?
I did the same.
No Exxon Valdez, no bent or broken parts or scuff marks on anything, just a mystery.
I did experience jamming of the aperture lever while tightening the screws on the bayonet mount when putting it back together. Wiggling the lever while cranking down on the screws took care of it.
End result of the dis-assembly and look-see is a working DFA 100 WR macro with snappy aperture and no answer to why it was sticky in the first place.