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04-25-2021, 03:21 AM   #1
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Pentax KM - lens sets itself to smallest aperture

Hi all. I have this strange thing going on. My Pentax KM film camera works without any problem with all lenses I have. However, for the last few days, whenever I attach my SMC Pentax-M 1:2.8 28mm lens, the aperture ring turns by itself and resets to the smallest f stop of f/22. This only happens with this lens. I thought it might have something to do with the fact I've been using it a lot adapted to a Fujifilm X-T3 -- but all other lenses have been working fine despite being adapted as well. Any ideas?
Thanks!

04-25-2021, 06:19 AM   #2
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Sounds like the aperture mechanism is damaged - check the tab/pin that sticks out of the camera-side of the lens for damage.
04-25-2021, 07:56 AM   #3
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QuoteOriginally posted by raindog Quote
Hi all. I have this strange thing going on. My Pentax KM film camera works without any problem with all lenses I have. However, for the last few days, whenever I attach my SMC Pentax-M 1:2.8 28mm lens, the aperture ring turns by itself and resets to the smallest f stop of f/22. This only happens with this lens. I thought it might have something to do with the fact I've been using it a lot adapted to a Fujifilm X-T3 -- but all other lenses have been working fine despite being adapted as well. Any ideas?
Thanks!
The physical ring is turning? Can you turn it wide open once mounted it is it stuck at that position? Can you share a photo of the rear of the lens?
04-25-2021, 08:21 AM   #4
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The camera works as normal with all other lenses, and this lens works as normal when attached to the fuji camera. But this one lens on the one Pentax body does the following - see video here: Shared album - Pierre Friedmann - Google Photos.
Back of lens looks like in the attached picture.
Thanks!

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AC2003  Photo 
04-25-2021, 09:06 AM   #5
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I think we'll also need a picture of the other side.
The photo you have included is of the actuation lever, which closes the lens when the photo is taken.
That one doesn't move with the aperture ring, but there's another lever on the other side, recessed in a slot, that follows the aperture ring around... so it moves when the aperture ring moves...
That other lever interfaces with a tab in the mount of the camera to tell the camera what aperture you've selected.

-Eric
04-25-2021, 10:00 AM   #6
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QuoteOriginally posted by TwoUptons Quote
I think we'll also need a picture of the other side.
The photo you have included is of the actuation lever, which closes the lens when the photo is taken.
That one doesn't move with the aperture ring, but there's another lever on the other side, recessed in a slot, that follows the aperture ring around... so it moves when the aperture ring moves...
That other lever interfaces with a tab in the mount of the camera to tell the camera what aperture you've selected.

-Eric
Right. Here it is:
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04-25-2021, 08:34 PM   #7
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I'm still not clear - is the actual physical aperture ring moving to f22 or only the iris stopping down to f22.

04-25-2021, 08:55 PM - 1 Like   #8
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QuoteOriginally posted by UncleVanya Quote
I'm still not clear - is the actual physical aperture ring moving to f22 or only the iris stopping down to f22.
No. I can set it to whatever f stop, then as soon as I attach it the ring turns by itself to f 22. See the video in the link I shared above.
04-25-2021, 09:36 PM   #9
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QuoteOriginally posted by raindog Quote
No. I can set it to whatever f stop, then as soon as I attach it the ring turns by itself to f 22. See the video in the link I shared above.
That means that the aperture actuator is not engaging the coupler in the camera or that the aperture mechanism is not proper. When the lens is off-camera and the aperture ring at f/22, is the aperture full-open or full-closed or somewhere in-between.


Steve
04-25-2021, 09:41 PM   #10
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QuoteOriginally posted by stevebrot Quote
That means that the aperture actuator is not engaging the coupler in the camera or that the aperture mechanism is not proper. When the lens is off-camera and the aperture ring at f/22, is the aperture full-open or full-closed or somewhere in-between.


Steve
When the lens is off the Pentax body, or attached to any other camera it works fine. Also when any other lens is connected to the Pentax body, everything works fine. That's the misery, everything seems to be working, just not when this specific lens is attached to this specific body... Needless to say they used to work fine together too...
04-26-2021, 04:00 AM   #11
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Firstly looking into the camera, the actuating lever should be in the position shown below. If moved by hand it should return to this position rapidly.



On the back of the lens, the lever should be in the positions as shown below, the lever will move when the aperture is changed. It should not be possible to move the lever by hand.
Although if the lens has been declicked (the physical stops to the aperture ring removed) then this may be possible.



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Canon EOS 7D Mark II  Photo 
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Last edited by Ray-uk; 04-26-2021 at 08:36 AM.
04-26-2021, 05:11 AM   #12
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QuoteOriginally posted by raindog Quote
No. I can set it to whatever f stop, then as soon as I attach it the ring turns by itself to f 22. See the video in the link I shared above.
I get an error, “the album is empty”. Could be on my end?
04-26-2021, 05:56 AM   #13
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QuoteOriginally posted by UncleVanya Quote
I get an error, “the album is empty”. Could be on my end?
Sorry, here it is again: Shared album - Pierre Friedmann - Google Photos
04-26-2021, 06:03 AM   #14
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QuoteOriginally posted by raindog Quote
That’s freaky. I assume the aperture on this lens is de-clicked? Maybe the person who said that connected something wrong in the lens?
04-26-2021, 07:38 AM   #15
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QuoteOriginally posted by Ray-uk Quote
Firstly looking into the camera, the actuating lever should be in the position shown below. If moved by hand it should return to this position rapidly.



On the back of the lens, the lever should be in the positions as shown below, the lever will move when the aperture is changed. It should not be possible to move the lever by hand.
Although if the lens has been declicked (the physical stops to the aperture ring removed) then this may be possible.


I understand there should be pictures here but for some reason I can't see any...
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