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04-11-2009, 06:19 AM   #1
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Adaptall PKA adapter works on K100D, not so well on K20D?

I recently picked up from a local sale a Tamron 90mm F2.5 and Adaptall 2 PKA adapter for a good price.

Everything works perfectly on my K100D - but on the K20D, it doesn't recognize the aperture unless I physically push up on the lens. This seems especially weird as the contacts are closer to the bottom. Attempting to twist it makes no difference, pushing in on the whole lens doesn't do it... only pushing up helps. Occasionally it will keep the connection after releasing upward pressure but only until it has the slightly movement in another direction. Meanwhile, on the K100D, it works great even if I put pressure in any direction.

Has anyone seen this before and/or have an idea for a fix? I'd like to sell the lens (it's kind of redundant with my Dine 105mm) and keep the adapter and pick up some other Adaptall lenses, but the inability to work consistently is holding me back. The connections on the adapter look fine and it's overall in very nice shape.

I was thinking about trying a little brush-on conductive paint to enlarge the contacts just a tiny bit to see if that would help make the connection more consistently - any thoughts on this idea?

04-11-2009, 08:41 AM   #2
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I had the same problem, 'A' adapters that worked better on my K100D Super than on my K10D and K20D. Eventually I ran across this thread that helped to mostly solve the problem:
https://www.pentaxforums.com/forums/pentax-lens-articles/50689-fixing-tamron-...a-adapter.html

I still found that some lenses would loose the ability to transmit aperture info if you twisted the lens the wrong way on a K20D body. It happened more often with a heavy lens like the 300mm f/2.8 than with the smaller 135mm f/2.5 I had.
04-11-2009, 11:15 AM   #3
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Wow, that was easy. I've been looking for a fix for a couple months but I guess I hadn't found the right combination of words to search for. Thanks!

It is working much better now (even though there's no real obvious change in the height of the screw, it's just scratched up a bit around it)... but one thing I do notice is that if I twist it slightly, the max aperture changes between F2.4 and F2.8. The correct max is F2.5 - which I occasionally see very briefly when it's jumping between the two settings.

I don't know exactly what the mount is trying to tell the camera - I wouldn't be surprised if it's not relaying the exact correct information - but it's strange. FWIW, on the K100D, it showed F2.8 as the max (I haven't tried mounting it back on there yet.) From a few quick test shots, I don't see much different in DoF between F2.8, F2.5, and F2.4. The latter are slightly darker than the F2.8 which would make me think that it's not changing the aperture any, just using a faster shutter speed. Strangely, F2.4 seems a tad darker than F2.5 even though the shutter speed and ISO are identical. Strange indeed!
04-11-2009, 12:26 PM   #4
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Glad it is working better for you. Maybe try a little more gentle scraping on #3.

I had the exact same experience with the exact same lens and AD-2 mount on my K10D. I gently scraped screw head #3 with the tip of a pen knife, then cleaned with Residual Oil Remover.

FWIW, everything works perfectly and consistently now @f/2.5 & up.

Wonderful lens, AMAZING snap into focus and really sharp pictures. I found a MIB 01F 2x TC for literally less than the cost of shipping - there is no degradation of sharpness or IQ.

Just an amazing lens - I might actually sell my Viv S1 105/2.5. PM me if you need more help. I kept all the contacts on the Forum who helped me.

04-11-2009, 12:57 PM   #5
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What does your lens show for max aperture? The "correct" F2.5 or something else?

It seems like a nice enough lens but I'm not sure that it is quite to the level of the Lester Dine 105mm, but to be fair to the Tamron, I've barely used it yet. I don't have the 1:1 adapter and I'm not sure how hard I'd look for it, since I'm mentally ready to let the Tamron go. (I got the lens and adapter for less than a PK/A adapter usually sells for alone, so that's how I justified buying them - make a small profit and get a free adapter in the process!)
05-20-2009, 07:19 AM   #6
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Groucho, I have a lester a dine on a pka on a chinon cp-7m. Do you know if it will mount on a k100d super? Do you know of any other dslr's it will be compatable with? Thanks.
05-20-2009, 08:07 AM   #7
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It looks like your Chinon takes standard Pentax K-mount lenses so yes, all your lenses will work on any Pentax DSLR including a K100D Super. The Lester A Dine 105mm is a fantastic lens!
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