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07-18-2012, 02:28 PM   #1
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Stuck focus ring (Pentax-A 50mm F/1.7

Just got this lens today and I was curious if anyone had any advice regarding a stuck focus ring. I can't move it at all. I am good with my hands and have taken other lenses apart, so I don't mind taking a shot at this one.

07-18-2012, 02:49 PM   #2
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Hope this helps

This seems to be a common problem for the A 50mm F 1.7.
There was a thread about it sometime back that offers a solution:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/23058-pentax-5...-troubles.html

I fixed mine, so it isn't that difficult a fix
07-18-2012, 02:54 PM   #3
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Stuck aperture is typical - stuck focus I have not heard of.
07-18-2012, 03:50 PM   #4
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Ya - that thread is for a stuck aperture, not a stuck focus ring. Anyone else?;-)

07-18-2012, 04:18 PM   #5
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oops!

Guess, I didn't read the question well enough.
11-08-2018, 12:09 AM   #6
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Hi

Same problem with the jammed focus ring.
Anyone? (:



thanks

(I know the post is a bit old)
11-08-2018, 02:30 AM   #7
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QuoteOriginally posted by krajan Quote
Hi

Same problem with the jammed focus ring.
Anyone? (:



thanks

(I know the post is a bit old)
Welcome to the forums

There really are only a few things that can cause the focusing ring to jam on a simple prime lens like this... Either (a) the lubricants in the focusing helicoid have dried out, (b) dirt and/or debris has become lodged in the focusing helicoid, or (c) something is stopping the optical block from moving back and/or forward (perhaps something broken off internally). Either way, the solution is to dismantle, clean and re-lubricate the lens.
11-08-2018, 09:30 AM - 1 Like   #8
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I have seen a few A50/2 lenses with jammed focus rings. These had evidence of being dropped. Usually they had evidence of someone trying to fix the problem by extra force on the focus ring, like the rubber grip coming off. The fix is to remove the beveled trim ring around the front element, remove the three screws holding on the front barrel, and remove the three screws holding on the focus ring. Possibly these are loose from that extra force. Those three screws went into an aluminum ring with inner and outer threads, mostly hidden from view. The inner threads are large and move the lens elements in and out for focusing. The outer threads are fine-pitch and threaded into the lens body. I think on the A50/2, the mating threads are plastic. A sharp impact can cause the fine pitch threads to partly jump tracks and wedge the aluminum ring firmly in place. If this is the problem, you should be able to see the aluminum ring is slightly tilted. What I've done is find the low spot and use wedges to push it up. You can use a flat-blade screwdriver but that will dent the plastic. I use wood, but if you want to buy something, find an auto parts store and buy a set of plastic tools for interior body work, maybe $10. These are meant for removing door panels or plastic trim and have many useful wedge-shaped ends. Harbor Freight has them. You'll know when the aluminum ring snaps back into place. It should turn after that. You have to reset the infinity focus again when you attach the focus ring. That is similar to most Takumar or Pentax manual-focus primes.

The A50/1.7 is pretty much the same construction and that's my guess. I just haven't seen one jammed. Maybe the 1.7 owners were more careful. Anyway, if you don't lose the six screws the repair should be easy and you will feel like a hero.


Last edited by Just1MoreDave; 11-08-2018 at 09:35 AM.
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