[Sluggo]

I wonder if anyone else has run across this problem with an SMC-A 50mm f/1.7 or similar lens: the aperture ring doesn't always turn freely. It's okay between f/1.7-f/5.6, but if you try to close it down beyond that it sometimes sticks. Apparently the problem is the mechanism under the little release button that lets you get in and out of the 'A' position; while you hold that button down, you can move the ring to any position.

Optically the lens is fine, and I've experimented with it in the A position on my DL and found it works in all picture modes. But my plan when buying this lens was to use it on an older manual camera, and in that context the aperture ring hangups would be an annoyance.

I'm mechanically inclined, so was thinking about trying to take the lens apart to see if there is anything I can do - but first, has anyone run into the same problem before, and is it a simple fix? If not, the thing to do is to leave it intact, not risk having it fly apart in a thousand pieces on my workbench, and find someone who wants to use it in A-mode on a newer camera.

It would be fine on my *istDL, but I don't need it for that, because I snagged one of the last FA50/1.4 lenses in the world a few weeks ago.

[Ole]

I have a similar problem with exactly an A 50/1.7. It appears to me that Pentax switched to plastic for the ring on the 1.7, whereas the 1.4 is metal. My 1.4 performs flawlessly, whereas the 1.7 is less than perfect. On mine it is in the 4.0 - 2.8 - 1.7 end of the ring that it is "sticky". I suspect that the pastic changes shape over time.

Would definitely be interested in your experience when you pull yours apart!

[Sluggo]

Would definitely be interested in your experience when you pull yours apart!

Haha - how 'bout you first?

[Ole]

Sure, send me your lens!

[Arjay Bee]

Try this for starters:
http://homepages.ihug.co.nz/%7ESrawhiti/pentax50mmf1.4.html

I have seen elsewhere that you then soak the blades in lighter fluid to dissolve the grease that has gotten on to the blades to make them stick. blow dry with a warm hairdryer and reassemble.

Good luck

[Sluggo]

Thanks - interesting to see the disassembly - hopefully the lenses are similar enough that it will be helpful. It seems odd to me to go from the front of the lens toward the back, although fungus was what this author was after. I was going to start at the mount end, because that's where the visible screws were, and the aperture ring is back there anyway -- I wonder what difference it makes. Maybe it's just correct to work from the other end?

FWIW, the iris blades in this one are fine - it's the adjustment ring that is messed up. From the way it feels, I'm guessing it's not gunk I'll find in there, but honest wear -- not something I expect to fix by cleaning. Still I won't know till I look...

[rola]

There's a discussion of this problem, with directions to fix it (and pictures of the process) on the Pentax board at DP Review -- search for "Fixed snagging aperature" in the Thread Title...I'm new here, and don't know the protocol for linking to other boards, so I don't want to step over the line by posting the actual link.

Rob H.

[Ole]

Thanks - interesting to see the disassembly - hopefully the lenses are similar enough that it will be helpful. It seems odd to me to go from the front of the lens toward the back, although fungus was what this author was after. I was going to start at the mount end, because that's where the visible screws were, and the aperture ring is back there anyway -- I wonder what difference it makes. Maybe it's just correct to work from the other end?

FWIW, the iris blades in this one are fine - it's the adjustment ring that is messed up. From the way it feels, I'm guessing it's not gunk I'll find in there, but honest wear -- not something I expect to fix by cleaning. Still I won't know till I look...

I agree that you start from the back in your case. Here is a link regarding disassembling the mount (and more...) of an F 70-210:

http://members.shaw.ca/hargravep/70-210.htm

[Sluggo]

I thought it might be time to report on this as a partial success: rather than working only in A mode, the lens now works only in M mode. The problem was, as somebody in one of the above-referenced threads mentioned, one of a pair of spring metal clips held in place by plastic welds. The welds look pretty thin to start with, and they must have grown brittle with age, When one of them broke, the spring clip was left rattling around in there getting stuck in various positions.

I was able to retouch the weld and get the spring clip back in place, but was unable to get all the other bits in place -- after a lot of putzing and puzzling over where things belonged, I thought I had it figured out, when one of the bits slipped out of my fingers and vanished into nothingness, never to be seen again. As "mechanically inclined" as I like to think of myself, my aging fingers and eyes weren't up to this particular fine motor task. Anyway it had come to me for next to nothing on an as-is camera and now it's essentially an M lens forever, so I'm pleased enough to be able to use it on a (different) manual camera.

[Tonytee]

I wonder if anyone else has run across this problem with an SMC-A 50mm f/1.7 or similar lens: the aperture ring doesn't always turn freely. It's okay between f/1.7-f/5.6, but if you try to close it down beyond that it sometimes sticks. Apparently the problem is the mechanism under the little release button that lets you get in and out of the 'A' position; while you hold that button down, you can move the ring to any position.

Optically the lens is fine, and I've experimented with it in the A position on my DL and found it works in all picture modes. But my plan when buying this lens was to use it on an older manual camera, and in that context the aperture ring hangups would be an annoyance.

I'm mechanically inclined, so was thinking about trying to take the lens apart to see if there is anything I can do - but first, has anyone run into the same problem before, and is it a simple fix? If not, the thing to do is to leave it intact, not risk having it fly apart in a thousand pieces on my workbench, and find someone who wants to use it in A-mode on a newer camera.

It would be fine on my *istDL, but I don't need it for that, because I snagged one of the last FA50/1.4 lenses in the world a few weeks ago.

I do now have the same problem with my SMC-A 50mm 1.7 lens. The aperture does not become unmovable, however it is difficult to make adjustments. It takes a lot more force to move the ring in any direction. The A button works just fine, but the rest of the f stops are tough to move. Thanks for reading. I wonder how long the lens can last in this condition. Anyone have any idea on the cost to repair?

Tonytee

[Not a Number]

This is a common problem with this lens. See this thread as to the causes and how to fix it:

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/88051-pen...ng-repair.html