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02-18-2010, 09:26 PM   #1
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What mechanism causes aperture ring clicks/snaps?

Ok I know there are some lens dissectors here, I recall a post replacing the little metal fingers with some household item. This should be easy!

I've taken my F 50mm 1.7 apart to investigate a situation with the focus gears feeling rough

Everything went ok, didn't really solve the problem but at least I have a better idea of what is going on inside now. Theres very few gears to go wrong which I'm pleased about, no missing teeth or anything.

Anyway, I got it back together without any leftover parts. Everything is great except:

When I turn the aperture ring, the aperture functions with no hard stops, it is completely smooth without the half-stop clicks.

I can see on the aperture ring where the indentions are to make it click, but I can't figure out, what interfaces with those to make it snap?

Pardon the poor photo


02-18-2010, 09:34 PM   #2
pbo
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You probably lost a small ball bearing - can't really tell where it goes from the photo though. Those are quite tricky to notice when you're disassembling and hard to find if you lost them - good thing they're cheap though. Micro-tools sells them here - but it's kind of a guesswork to find the right size that would make apertures click - but not overly stiff.
Or, if you've got a cheap FA/F donor lens - you can just get it from there.
02-18-2010, 09:43 PM   #3
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There is (was) a ball bearing trapped between the aperture ring and the lens body, with a spring pushing it outward. The bearing makes the clicks as it moves in and out of those grooves you saw. Here's a photo of the bearing perched on its spring on an A50/1.7:



The spring launched the bearing into another dimension when you slid the aperture ring off. The bearing is probably 1.5mm. You can find them at Micro-Tools. I don't know where to find the spring, so I hope it's still there. Micro-Tools also has some light focusing grease which might help your other problem. It's a little pricey though. I have an F28/2.8 with the same issue, and it helped but wasn't a total cure.
02-18-2010, 10:12 PM   #4
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Wow thanks, I know the hole even I think. That's funny because I've already spent a good bit of time on the floor looking for things that I dropped. Even if I find it, getting that in doesn't look like much fun.

I have wood floors at least, and I've found that a flashlight parallel to the floor lets you find just about anything.

It still works as-is but I would like to get it back to like new if I ever want to sell it. I paid $75 for it last year and now I see them going for nearly $200

02-19-2010, 06:19 AM   #5
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QuoteOriginally posted by mrcrontab Quote
Wow thanks, I know the hole even I think. That's funny because I've already spent a good bit of time on the floor looking for things that I dropped. Even if I find it, getting that in doesn't look like much fun.

I have wood floors at least, and I've found that a flashlight parallel to the floor lets you find just about anything.

It still works as-is but I would like to get it back to like new if I ever want to sell it. I paid $75 for it last year and now I see them going for nearly $200
Pentax used to have these parts and there not expensive. Not sure about that anymore.
They are tiny and hard to find since they roll so well..... especially when launched.
02-19-2010, 07:33 AM   #6
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Don't forget you'll also need the spring behind the ball. Hope you didn't lose that as well.
02-19-2010, 08:29 AM   #7
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I played carpet patrol and didn't find it, however there is an old konica 50mm here that I can't use, and it just happens to have a lens mount full of conveniently sized ball bearings

It is back together now and clicks at the stops as it did before. Learned my lesson!

Of course after reading this I found the numerous guides on using a plastic bag and warning about the spring.
02-19-2010, 09:13 AM   #8
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Aha, found the real parts

Method: use swiffer to sweep floor dust into a pile, then apply neodymium magnet

02-19-2010, 09:22 AM   #9
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a lens with a continuously variable aperture is sometimes a benefit!
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