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09-30-2010, 08:37 AM   #1
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KX sticky aperture follower

OK, I know the answer is to send it to Eric which I may end up doing, but meanwhile I'll try to find if there's a simple solution to this.

In the camera mount, there's the aperture follower, it's like a ring that rotates around the mount, pushed by the aperture tab on the lens. This bit tells the meter circuit the aperture the lens is set to.

On my KX, the issue started as an occasional refusal to meter, fixed by remounting the lens. I also noted that closing down the lens had more resistance than opening it up. Actually this is how it still behaves - though recently when I moved the aperture follower by hand, I think I heard it squeaking.

Everything else on the camera works fine.

What's the fix?


09-30-2010, 09:40 AM   #2
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The "follower" is spring-loaded and should have resistance when moved clockwise (facing the body), so you would expect a little greater resistance when mounting the lens than when removing it. There may also be more resistance when moving the aperture ring to the wide end. Stickiness on the return is another matter. I would suspect damage (bent/deformed ring) to the assembly, perhaps from an ill-fitting lens or a third-party M42 adapter over-rotating in the mount.

You may be able to gain access to the assembly by removal of the mount face, but as always, there is some risk!

09-30-2010, 10:35 AM   #3
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That's what I was thinking - the resistance is more than typical for these Pentaxes so I'm suspecting dirt along the path, especially now that it squeaks. It doesn't stick on the return, or not much anyway. I'll take a look at what's behind the mount face, virtually of course
10-01-2010, 06:16 AM   #4
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I tried spraying air around the ring, in case there is dirt... if anything it made things worse, the ring is definitely sticking. I think it's off to Eric for the camera.

10-03-2010, 03:43 PM   #5
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Ack - slow reply. I was vacationing the last few days, with no Internet.

A couple of years ago I bought an MX with that symptom, and close inspection showed that the coupling tab (the part of the ring that protrudes into the lens body) was slightly crooked. Conclusion was that the ring was sticking not because of any dirt or corrosion, but because it was binding inside. Maybe the previous owner simply had trouble mounting or unmounting a lens once.

The permanent cure was a tiny little tweak with needle nose pliers. It freed right up, and has stayed fixed to this day.

That said, I more recently acquired a KX with a sticky aperture ring, but since it also had a bad light meter, I didn't want to risk [un]bending anything, and instead sent it to Eric, who did a fine job fixing both problems.
10-18-2010, 01:41 PM   #6
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My Minolta XD5's aperture follower tends to stick around f/8 in humid conditions, but my Pentax hasn't had that problem, probably because it's inside the bayonet.

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