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05-18-2009, 03:16 PM   #1
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M 50mm/1.7 - aperture ring stuck

I just received this lens after buying it on ebay, and it was reported to me as being fully functional. However, it turns out that the aperture ring is stuck at f/22, and therefore so are the blades. Using the aperture lever, I can open the aperture, and the blades move smoothly. I can't even get the ring to jiggle, though, let alone turn. I've contacted the seller, but if possible I'd rather just get this fixed. Any suggestions as to what I could do? I've seen a few other threads here about 50/1.7s with stuck apertures, looks like it's a bit of a trend.

05-18-2009, 04:33 PM   #2
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QuoteOriginally posted by jzietman Quote
I just received this lens after buying it on ebay, and it was reported to me as being fully functional. However, it turns out that the aperture ring is stuck at f/22, and therefore so are the blades. Using the aperture lever, I can open the aperture, and the blades move smoothly. I can't even get the ring to jiggle, though, let alone turn. I've contacted the seller, but if possible I'd rather just get this fixed. Any suggestions as to what I could do? I've seen a few other threads here about 50/1.7s with stuck apertures, looks like it's a bit of a trend.
In my experience it has been the A50/1.7, not the M, that has a recurring problem with the aperture ring. There is a heat-welded plastic retainer inside the A (and only the a50/1.7, no other Pentax lens of that period or earlier has it) that can come loose and block the ring from turning. Your M lens must have something else loose.

Try looking in the Camera Repair and Service Forum here and emailing Eric Hendrickson and Ralph Innes for their terms and advice. Both are excellent technicians.
05-18-2009, 07:31 PM   #3
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I've gotten the ring to move now, and I can get it to all of the different settings. However, the ring is still very stiff, especially at the two extremes of its setting. Any "home remedies" for this? I'm betting it's just some kind of grime under the ring from a good bit of use.
05-19-2009, 08:40 AM   #4
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Find a good place to work where you can keep track of small parts. You can get to the aperture ring by taking off the mount, five screws on the back. The aperture ring can just slide off now, but watch for a small ball bearing trapped between the ring and the lens body. It's where the orange diamond is on the depth of field scale. Here's a photo showing the mount and ring removed, with the bearing in place on the left:



It sounds like you can just clean the ring, apply a small amount of good quality grease to it and reinstall.

Here's an album of photos for more disassembly of that lens, some tools, etc.:

Picasa Web Albums - David - Disassembly

05-19-2009, 10:04 AM   #5
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Would parafin wax jelly be acceptable as grease? That's all I have for now.
05-19-2009, 01:52 PM   #6
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Probably not. The grease needs to have a high temperature rating so it won't vaporize and end up on the lens or aperture. No grease is OK, the grease helps things work smoother though. I use lithium multipurpose grease.
05-19-2009, 02:45 PM   #7
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Did you consider return the lens?

I just sold one on ebay. Mine copy is perfect when I inspected it. If you bought it from someone in Toronto, that might be me. I will grant a return if the ring stuck.
12-12-2009, 05:11 PM   #8
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First of all, I'd like to say this thread and pictures have been very helpful. I started off with a M 1.7 50mm with a slack aperture ring, improperly calibrated focus ring and dirty inner elements. My focus is now right on, aperture ring clicks into all positions and glass is clean.

However just like before I started doing any work, when I put the lens on a camera body, the camera does not recognize the lens. By that I mean it won't show any variation in meter reading as I turn the aperture ring.

I also checked when the camera fires if the blades close down fast and properly and they do. Same is the case when I test it with the DOF preview lever.

Any ideas?


Last edited by Halco; 12-12-2009 at 08:48 PM.
12-12-2009, 05:52 PM   #9
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QuoteOriginally posted by Halco Quote
First of all, I'd like to say this thread and pictures have been very helpful. I started off with a M 1.7 50mm with a slack aperture ring, improperly calibrated focus ring and dirty inner elements. My focus in now right on, aperture ring clicks into all positions and glass is clean.

However just like before I started doing any work, when I put the lens on a camera body, the camera does not recognize the lens. By that I mean it won't show any variation in meter reading as I turn the aperture ring.

I also checked when the camera fires if the blades close down fast and properly and they do. Same is the case when I test it with the DOF preview lever.

Any ideas?
I assume you are fitting the lens onto a dSLR? If so, you might want to review the manual lens tutorial (https://www.pentaxforums.com/forums/pentax-beginners-corner-q/59272-shooting-...x-dslrs-f.html). With your Pentax-M lens, there is no communication between the lens and the camera. The body does not "know" that you are changing the aperture. To use this class of lens, change the mode to "M" and use the green button or DOF preview lever to adjust the metering.

Steve
12-12-2009, 06:16 PM   #10
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Actually, I'm fitting it onto a film SLR. Same result from a P3, P5, and Super Program.

With some further testing, the lens meters properly with the DOF lever depressed as I turn the aperture ring but not without.

Thanks for any input.
12-12-2009, 09:19 PM   #11
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QuoteOriginally posted by Halco Quote
Actually, I'm fitting it onto a film SLR. Same result from a P3, P5, and Super Program.
On these cameras, the camera has a lever called the aperture simulator that fits into a slot on the lens. It moves when the aperture ring moves, so the light meter can read the aperture ring setting. The slot in the lens is opposite of the aperture lever. You should see a metal finger in the slot that moves when you turn the aperture ring. The photo above of the lens with the mount and aperture ring removed shows this finger at the bottom center, with a protrusion below it that connects to the aperture ring. This photo shows the full part on the right. Your lens might be missing this part, or incorrectly assembled so it's not functioning right.
12-12-2009, 09:32 PM   #12
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QuoteOriginally posted by Just1MoreDave Quote
Find a good place to work where you can keep track of small parts.
A baking tray. FOR THE LOVE OF THE GODS, a baking tray.

Better still, use a glass one with a sheet of white paper under it.

Trust me on this.
12-21-2009, 12:59 PM   #13
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Pentax-M 50mm f/2 with stuck aperture lever

Hello all,

I've nearly the same problem, except rather than the aperture ring being jammed, it is the lever which stops down the aperture.

It is stuck in "stop-down" position, so that the blades never fully open.

The ring rotates to all positions except 2.0.

I assume (so dangerous) that I can simply follow the steps above for disassembling the back and free things up. Before I do, I wanted to drop in and ask if there's anything different about this issue. Could it be deeper than the steps outlined? I'm not at all comfortable attempting this, but I acquired the lens at a very low price and why not give it a shot, eh? Thanks!
Chris
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