Good evenig!

Some months ago, I bought a used SMC-A 20 2.8 lens, which in this period is my most used lens. I was on a hike this weekend, the camera was well protected in my backpack, but when I wanted to take a picture of reflections in a lake, I noticed that I could not focus to infinity anymore. I did not want to force anything, so I put the lens away and looked at it at home: one aperture blade shifted; it moves with the others, but it "lags behind", it does not open compleately at f/2.8 and at f/16 it block almost the entire pupil. I can't focus to infinity any more independently of the chosen aperture, the focus ring does block earlier than usual.

Has anyone of you ever taken apart an SMC-A lens? I have cleaned and/or repaired several SMC-M lenses (with fungus) and a FA 50 1.4 (where the focus barrel detached), but I never took apart an A lens. I certainly have JIS screw drivers, but before opening the lens, I hope to get some suggestions / pieces of advice how to proceed / what might have happened / if this happened to you / how to fix it.

Best regards,
Rapfl

[Rapfl]

Oh well, I opened the lens from the back to get to the diaphragm mechanism, which is broken; first of all, it's a much more difficult construction than the SMC-M lenses I cleaned / repaired so far; evidently I am not the first person to open the lens, as some internal screw heads are pretty much stripped; I have JIS screw drivers so at least I managed to remove most of them, but one last screw is stripped so deeply that the head has a conical hole instead of a cross (the equivalent screw on the other side does have a cross, so it's not a feature, as I can also tell from the metal dust...).
Not sure how to remove this one (I guess it's the last I need to open the diaphragm mechanics and put the blades to their original position)....

Raphael

[jimr-pdx]

Ouch that's sad news. I suppose you could drill it out and rely on the other screws to keep things in place, assuming all other repairs go well. I have the f/2.8 1:2 macro version, so I understand why you like your lens so much!

[Dicknet]

Oh well, I opened the lens from the back to get to the diaphragm mechanism, which is broken; first of all, it's a much more difficult construction than the SMC-M lenses I cleaned / repaired so far; evidently I am not the first person to open the lens, as some internal screw heads are pretty much stripped; I have JIS screw drivers so at least I managed to remove most of them, but one last screw is stripped so deeply that the head has a conical hole instead of a cross (the equivalent screw on the other side does have a cross, so it's not a feature, as I can also tell from the metal dust...).
Not sure how to remove this one (I guess it's the last I need to open the diaphragm mechanics and put the blades to their original position)....

Raphael

I had exactly the same problem with a 35mm Kodak Camera in my collection. In my case it was caused by the pivot point that the blade moved on being totally worn through and there was nothing that could be done. It was a pity because up until then it was a nice usable Camera but it is now an ornament.