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07-31-2015, 03:57 PM   #1
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Aperture not opening fully - ring issue?

I've got a Petri 28mm F2.0 that won't open to F2.0. By this I mean that it will open to F2.8, but when I attempt to move the ring round it only budges a little and doesn't go all the way. Furthermore, it doesn't close past F5.6, and adjusting the aperture darkens the viewfinder. Hopefully the seller will take it back and fix it, but should they be unwilling, or this issue sound familiar and fixable to you lovely people, I may as well try to sort it myself.

This ought to be a pretty good lens; my 50mm is lovely, and the limited reviews seem pretty happy with it as well.

07-31-2015, 04:14 PM   #2
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I think there are a number of issues that could be at hand here, but I will say...

I got a second hand Rikenon 28/2.8 in a batch of old m42 lenses I bought on a local swap site. It had the same sort of issue. Obviously no oil or wear on the blades, so I did end up taking it apart. There was a sprung coil around the aperture assembly that had popped out of place. I snapped it back where it should have been and put it all back together, but a second tiny spring was, I presume, aged and stiff/stretched and, even though the aperture ring would turn and click until the cows came home, I could never get the aperture blades to correspond. I ended up selling it for a song on Ebay.

I have some pictures of my disassembly of the Rikenon that I can email to you. PM me if you want 'em, but I'm not sure how similar the lenses are.
07-31-2015, 04:28 PM   #3
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Since it's K mount it should not darken when you stop it down. Can you take it off the camera, and see if the aperture blades move when you move the aperture ring? Does the aperture level move while turning the Aperture ring? Does the aperture lever open it back up? Is this an A series or K series lens(i.e. is there contacts to camera body on mount)
08-01-2015, 04:13 AM   #4
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QuoteOriginally posted by ToyTank Quote
Since it's K mount it should not darken when you stop it down. Can you take it off the camera, and see if the aperture blades move when you move the aperture ring? Does the aperture level move while turning the Aperture ring? Does the aperture lever open it back up? Is this an A series or K series lens(i.e. is there contacts to camera body on mount)
The aperture moves when the lens is removed from the camera - though still not all the way open. The aperture is not read or adjusted by the camera body. There are no contacts on the mount.

QuoteOriginally posted by severalsnakes Quote
I got a second hand Rikenon 28/2.8 in a batch of old m42 lenses I bought on a local swap site. It had the same sort of issue. Obviously no oil or wear on the blades, so I did end up taking it apart. There was a sprung coil around the aperture assembly that had popped out of place. I snapped it back where it should have been and put it all back together, but a second tiny spring was, I presume, aged and stiff/stretched and, even though the aperture ring would turn and click until the cows came home, I could never get the aperture blades to correspond. I ended up selling it for a song on Ebay.

I have some pictures of my disassembly of the Rikenon that I can email to you. PM me if you want 'em, but I'm not sure how similar the lenses are.
That'd be handy, cheers.

08-01-2015, 04:49 PM   #5
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Okay, so I gave into my impatience and tried opening it up. I now have different ... issues. One of the first things I noticed was there was a short, tiny screw floating around.

Anyway, I put that to one side and tried had a deeper look. Nothing particularly worrisome was to be found. After poking around I put it back together (have you tried turning it off and on again?) and put it back on the K-30. Hey! The aperture works properly now; great (though the VF still goes dark when I stop down)! Oh, hang on, I left the end on the table - that funny bit that the aperture lever sits against. I put that on and now the aperture won't close past F4.

So at the moment I have an incomplete lens which opens and closes fine, but is missing the end ring thingy (and a screw from somewhere?) and darkens the aperture when it stops down. It's fine for live view or up to F5.6 I guess, but doesn't feel right.
08-02-2015, 01:20 AM   #6
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