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09-04-2013, 05:13 AM   #1
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How to disassemble F50/1.7?

Hi

Does anyone know how to disassemble an F50/1.7. I wanna fix the focusing. It is a little stiff from 0.8m to infinity.

09-04-2013, 11:34 AM   #2
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You can take off the front barrel by focusing to 0.45m and removing the three screws on the side. JIS screws as usual:



I think you can see the three screws that hold on the focus ring here, but don't just unscrew those and pull off the focus ring. You don't want to bend the part like in this thread:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/235890-what-pi...internals.html

It's possible that you can just work a small brush in where the barrel was and clean the visible threads, then work the focus and repeat. Some light focus grease might help and won't slow down AF. If that doesn't work, you may have to start from the mount. I know I've done this and gotten access to that contact brush, I just don't remember exactly how. Be careful not to lose all the tiny contacts and springs. I am pretty sure there's a bearing trapped under the aperture ring as well, and leaf springs like you'd see on the A50/1.7. See my thread on that lens in the Maintenance articles. Once you get the aperture ring off, there are 3 screws underneath it that separate the lens body. That's where my memory is not clear.
09-04-2013, 12:04 PM   #3
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Thanks for the answer. i'll test removing the front and brush it first. If it doesn't work I'll open i from the rear.

That metal brush thingy, where is it located?
09-05-2013, 03:34 PM   #4
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I don't remember exactly, and I probably don't have time to take mine apart to check. It wasn't hidden as in some other lenses, and I remember having to take the steps I outlined, I just don't recall the next part. (That's good, if it was hard I'd remember.)

09-06-2013, 10:42 AM   #5
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Ok. Now Im just waiting for my new JIS screwdriver to arrive before I can fix it.
09-19-2013, 10:41 AM   #6
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Just took mine apart and found the metal brush needed some adjustment. Some were bent but now it works fine.

For other people who want to fix their F50 I have a warning. The metal brush is connected with the focusing ring so be very careful when taking that out because the brush will get bent very very easily.
09-19-2013, 04:08 PM   #7
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I haven't opened up an F50/1.7 before, so I'm not sure it the following holds true for this lens.

I have repaired many F series zoom lenses and on some of them, you can access the fragile brush contact by peeling back the rubber that surrounds the barrel (or sometimes it's under the plastic bit). Once revealed, you should be able to unscrew the two screws holding it and remove the contact safely.
09-20-2013, 07:19 AM   #8
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That does make sense. The brush is outside the focusing ring so if it is accessible from the front it would be much easier to not break it, but I didnt pay attention when disassembling it. I just did it the spartan way.

09-21-2013, 02:10 PM   #9
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QuoteOriginally posted by striker_ Quote
disassemble
I just find this such a frightening word, let alone actually doing it.
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