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07-07-2011, 06:44 PM   #1
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Aperture ring not closing

Hi, folks.

I just got an old Asahi SMC Pentax-M 135mm with a faulty ring. Or a faulty aperture lever, I don't know exactly.
The problem is that the ring doesn't move the aperture blades, at least to close them. If I move the lever by hand to close the aperture, then the ring can open it, but once opened, everything is stuck again.

How can I fix this?

Thanks!

07-07-2011, 06:47 PM - 1 Like   #2
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Note that the aperture will never close when the lens is mounted- all the aperture ring does then is limit the maximum aperture to which the camera stops down.

When the lens is not mounted, however, the aperture should be consistent with the ring's setting. If it isn't, then there's something wrong with the ring- but as long as it limits the aperture when you try moving the lever, the lens should still be usable on your camera.

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07-07-2011, 07:10 PM   #3
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Thanks for the quick answer, Adam.

I got that lens with another two Asahi Pentax-M, a 28mm f/2.8 and a 50mm f/1.4. Both lenses work the way you described, with levers and rings moving together.

I guess I can set the aperture before I mount the 135mm and I will try that later, but is there a way to fix it?
07-07-2011, 07:27 PM   #4
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Perhap the aperture blades have oil on them and are sticky? That is one possibility. For example one of my m42 lenses sticks wide open until I force it via the pin to close the blade.

07-07-2011, 08:10 PM   #5
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I don't think so, the blades move fine with the lever and with the ring, when they are closed.
The only issue is to close the aperture with the ring, it doesn't work only that way.
07-07-2011, 09:07 PM   #6
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I started fooling around with mine and knocked a spring off. Now it works like yours. Does your aperture lever have any spring action to it? Or if you set the aperture ring to f32, can you move the lever to have the blades closed halfway and have the blades stay there even not holding the lever? If so, a spring might have come off. It looks like it might have stayed within the lens unless your lens was disassembled and the spring lost then.

I can take some photos tomorrow to show you where the spring needs to be reattached.
07-07-2011, 09:28 PM   #7
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Thanks, some pictures would be nice.

If I turn the focus ring to move the rear element away, I can see a little spring near the inner part of the lever. I' ll take a photo of that too, as soon as I get my camera, tomorrow morning.
07-08-2011, 08:09 AM - 1 Like   #8
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If the spring is knocked out of place then the lever that controls the blades will not move back to reset position if I recall. If it is indeed out of place you should be able to tell right away.

07-08-2011, 08:54 AM - 1 Like   #9
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The spring on the aperture lever pulls the blades closed or rather moves the lever to the position to Allow them to close, down to whatever position you have chosen with the aperture ring. So if you have your lens set to f22 (off the camera) and pull the lever to Open the blades, as soon as you release it, they should spring back without delay. I don't remember about Pentax M lenses but Some lenses have 2 springs. The one you see on the top and another located in the body near the aperture blades.

IF the lens does not work as described as above, one of 3 things has likely happened.

1. The spring has come loose.
2. The spring has become too weak to do the job.
3. There is oil or some other lubricant on the blades.

In the case of 3, you may or may not see it but it will always prevent the blades from Closing or cause them to drag in doing so, not from opening. That's why lenses with stuck apertures will Always tend to Over expose photos.



6500
07-08-2011, 09:29 AM   #10
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OK, here's my M135/3.5 with the mount removed. Red arrows show the upper and lower connections for the spring, which is loose on the right.



With steady hands, I reconnected the spring without further disassembly of the lens. I used a bent paper clip as a hook holding the top loop, put the bottom loop on its conection, and pulled the top loop onto its connection. Usual warnings: The mount screws are difficult without a tool that fits them well. When the mount is removed, the aperture ring can slide off.
07-08-2011, 10:11 AM - 1 Like   #11
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It is about 50 times easier to put the spring on if you focus the lens to 1.5M/5ft. first. Reinstalled:



And I switched 90mm macros for this shot. The Tamron 52BB 90mm f2.5 Adaptall-2 had a purple spot in the center of the frame from reflections between its flat rear element and the sensor.

Last edited by Just1MoreDave; 07-08-2011 at 12:33 PM.
07-08-2011, 07:17 PM   #12
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You all are very helpful.
Unfortunately none of my small screwdrivers fits the lens screws, so I will buy another one to open it. But the spring seems to be in the right place, just like in the last photo.
I will keep you posted. Thanks again.
07-08-2011, 07:44 PM   #13
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A screwdriver article, then:

https://www.pentaxforums.com/forums/maintenance-repair-articles/119344-cross-...s-caution.html

If you have a Phillips #00 or #000, you can unscrew the three screws holding on the flat black light shield. One of these screws is right next to the red alignment dot on the mount; the others are 120 degrees away from that one. Although these screws are still JIS, they aren't usually as impossibly tight as the mount screws, and easier to remove with the wrong screwdriver. Removing the light shield allows decent access to the spring and is a good alternative to mount removal.

If it's not that spring, I think you'll need to remove the mount, slide the aperture ring off and unscrew three screws that were hidden by it. Then probably you'll see the rest of the mechanism. I think there's a second spring in there. When you slide off the aperture ring, there's a ball bearing trapped between ring and body, near the orange diamond mark. Make sure that doesn't fly off into space.
07-08-2011, 08:26 PM   #14
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Good advice. The smallest Phillips in my set is a #0 and it doesn't fit at all. A slotted 1.4mm does, but I can't even think about using it. I will bring the lens with me and look for the right one.
07-10-2011, 07:32 AM   #15
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Pentax lenses use the JIS standard for screws. If you want to be accurate you can buy JIS screwdrivers. I don't know what your budget is, but a search on ebay brought up these.
Moody 4 Pc Extended Reach JIS Screwdriver Set/58-0405 | eBay
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