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11-21-2011, 05:17 PM   #1
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Just received a SMC Pentax-A - Aperture Ring Question

Hi. I just received a SMC Pentax-A 28mm f2.8 lens, and it seems that the aperture ring does not turn even though the button is pressed (I am able to turn it on the 50mm A that way). It seems though that the lens works fine on the camera. When I change the camera dial, the aperture readout in the display changes as it should. And, the exposure changes as it should. However, I am wondering if anyone has any ideas what I can do such that the aperture ring itself can be turned manually. Or, since it is on A and works fine in that mode, is it best just to leave it alone?

Thanks.


Last edited by Spodeworld; 11-21-2011 at 05:24 PM.
11-21-2011, 05:31 PM   #2
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I have read that the aperture ring on A series lenses can be finicky. If your lens works as it should for the entire aperture range in the AE mode, I would leave it alone. Only reason for turning the aperture ring would be if you are reversing the lens and want to be able to stop down, use other MF lenses instead.
11-21-2011, 05:34 PM   #3
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If the automation works I wouldn't worry about it, it might be a more involved repair.

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11-21-2011, 05:39 PM   #4
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Thanks..the automation seems to be working fine...maybe I'll leave well enough alone. I think I know what would happen if I ventured inside the lens anyway, and it wouldn't be pretty.

11-21-2011, 07:39 PM   #5
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The aperture ring on A lenses is rather wicked, I took my A 28mm f2 apart to re-lube the focusing coil, took me about 2 weeks to put it back together.
11-22-2011, 08:00 AM   #6
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Just the kind of horror story I was worried about. Of course, my story might end "I still haven't been able to put it back together." I should leave well enough alone. It works perfectly fine in A mode.

QuoteOriginally posted by VaSA Quote
The aperture ring on A lenses is rather wicked, I took my A 28mm f2 apart to re-lube the focusing coil, took me about 2 weeks to put it back together.
11-22-2011, 08:49 AM   #7
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The A lenses tend to have a spring come unglued that then lodges in the mechanism and prevents the ring from turning.
See Pentax 50mm lens fix
I have done this repair before on a 50mm and the important thing is to disassemble in a Ziploc bag because the tiny detent bearing may fly out.
However if yours is already on the A position and you don't plan to sell it you may just want to leave well enough alone.
11-22-2011, 08:49 AM   #8
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One reason that the aperture ring is finicky on A level lenses is that most of them have not been twisted in 15-20 years. But there is no reason to move it imo.

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