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01-28-2015, 03:30 PM   #1
deus ursus's Avatar

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SMC A 28/2.8 won't open up wide on K20D

I recently bought a used K20D, and when I tried my SMC A 28/2.8 on it (aperture ring set to A, of course ) I found that the camera wouldn't open the aperture up to more than f/4.0. It was no problem twisting the aperture ring all the way from f/22 to f/2.8, so the lens seemed fine. I then took the lens off, and found out that when I pushed the aperture actuator, it moved freely most of the way, but I had to use some force to push it that last bit to open the aperture up wide.

When I looked a bit closer, I discovered a piece of metal that the actuator stops against (see attachment), and when I push the actuator further, it pushes the metal piece out of the way, so to speak. Does anyone know if the lens is faulting, or if it's supposed to be that way? Is there any way I can fix it?

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01-28-2015, 05:10 PM   #2

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Can't really tell what's going on it the picture, but it sounds like someone removed the mount and then put it back improperly. There is a little piece that slides that should be aligned properly. I'm guessing it is not quite flush that way -- does it seem like the mount is screwed all the way down at each point? (Don't tighten it more.) Does it mount easily on the camera or is there a hitch?
01-28-2015, 06:24 PM   #3
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QuoteOriginally posted by vonBaloney Quote
Does it mount easily on the camera or is there a hitch?
If the lever does not work smoothly and with a snappy motion, I would use caution mounting it on the camera and might not attempt it at all. I cannot speak to the aperture mechanism in your K20D, but I have a K-mount film camera whose aperture coupler was ruined by a defective lens. You lens may be repairable, but I would not fiddle with it mounted to the camera until you are sure the aperture actuator is fully functional.

01-29-2015, 01:52 AM   #4
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I've had the lens for about 25 years, it was mounted to an ME Super that I bought used then. It has worked fine with both the ME Super and the LX that I bought a few years ago. The aperture ring turns as smoothly as one would expect all the way from f/22 to f/2.8, so I've never thought of it being faulty before I mounted it on the K20D.

I don't know what has been done to it before I bought it, so I don't know if it's been disassembled and reassembled improperly. Everything else seems tight.

01-29-2015, 05:38 AM   #5
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I have exactly the same lens. It doesn't behave in the way you describe - it has a smooth progression through the apertures right don to (actually, up to) f2.8. Looking at the actuator I can see there is 'something' tucked away in the body of the lens but it does not protrude nor does it get in the way of the actuator. I guess you have a problem with the lens,

Good luck with it.


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