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10-15-2010, 08:51 AM   #1
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Stuck aperture ring on A 50 1.7

I'm soon to be the owner of a 50mm 1.7 with a aperture ring that won't turn past f11 (teach me not to read the details on an ebay auction closely enough). I will be using it on a K-7 and as such would really like to be able to get it to "A"

Any ideas on how to go about freeing the ring? At this point, I don't feel like I've got much to lose, so I'm up to doing some disassembly and tinkering about.

10-15-2010, 08:53 AM - 1 Like   #2
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Sounds like a job for Eric. But if you really want to tinker I believe A series lenses disassemble from the rear. You'll need a #00 Phillips head.

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10-15-2010, 09:33 AM   #3
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I wouldn't reccomend dissassembling it unless you have experience. Unless of course you want a pile of parts in a ziplock bag . I think the aperture "stop" thing is a little bearing that is pushed by a spring into a detent and releases when you push on the button. It is tricky to get it back together. Sell it on ebay as a parts lens. Someone who knows how will snap it up and repair it. Or you could try jiggling it to get it in the A position. If you get it there, you never need to move it again. The plastic aperture rings on the A series are kind of crappy. I have heard the M series rings are much more durable.
10-15-2010, 10:53 AM   #4
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if you have the courage to do it yourself here is an excellent guide how to fix it.
https://www.pentaxforums.com/forums/pentax-lens-articles/88051-pentax-50mm-f1...ng-repair.html

10-15-2010, 12:09 PM   #5
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QuoteOriginally posted by boriscleto Quote
. . . if you really want to tinker . . . you'll need a #00 Phillips head.
Just a caution: Those screws that look like Phillips 00 and 000? They aren't. They're JIS cross-heads and life's a lot simpler with JIS screw driver bits.

Search "JIS screw drivers" -- Amazon's got 'em and whether you do this only once and run into trouble, or intend to do it often, it's worth your sanity to do it with the JIS tools so you don't risk stripping a screw head.

Otherwise, if gentle torque with the common Phillips jeweler-type tools doesn't work, file a flat-blade bit to the correct angle. Sooner or later, you'll be sorry if you don't as the Phillips bit makes a great roto-rooter in a tight JIS screw. You can see why here.

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10-15-2010, 07:45 PM   #6
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Your problem is extremely common issue with the A 50/1.7 and is caused by a broken plastic part in the aperture ring assembly. Hopefully you did not pay too much for the lens. The link above for doing the repair is helpful as is the advice regarding screwdrivers. I would suggest buying tools at Microtools:
Micro-Tools
They have just about anything you might need to service/repair a camera. Alternatively, you might just ping Eric Hendrickson for an estimate...
www.pentaxs.com
Eric does excellent work and is quite reasonable in his pricing.


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10-16-2010, 11:50 AM   #7
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Thanks for all of the information. The instruction thread and screwdriver information looks particularly helpful.
10-20-2010, 07:14 PM   #8
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Having done it myself, I strongly recommend the tip of de-construction in a deep, long, white tupperware container - extra insurance against springs flopping away. Also, strongly recommend a pair of little tweezers....and that little spring/steel nipple thing is a freaking headache to work with.

10-21-2010, 03:34 PM   #9
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Before you take it apart, give this a try. As Steve said, this is common with this lens and is caused by a plastic tab in the lens breaking off and jamming it. Try working the aperture ring back and forth while holding down the A lock button. It may take a while but sometimes by doing this you can get that little piece of broken plastic to shift and the aperture ring will move over to A. Of course once you get it there, leave it on A and use the camera to control aperture. I've had this happen with two of these lenses and have been able to get both to move by working it back and forth. One now resides on my K100D Super and the other is on my wife's Super Program.

CW
10-22-2010, 07:17 AM   #10
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Well, upon reflection, I decided that sending it to Eric (thanks boriscleto) was the better part of valor - and a more realistic appraisal of my chances of doing it right. I don't have it back yet, but I can say his price for fixing it was good - $40 with shipping.
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