Do you have a problem with a Tamron Adaptall PK/A adapter whose "A" functionality is not available or only if you do not completely mount the adapter to the camera, i.e., twist it back a little after mounting?

Chances are that it does not index on the body too far clockwise and that you can fix it within a minute.

The culprit may be one of the three screws which are fixed using a glue that electrically insulates them from the camera mount. If this is the cause of your problem then removing the glue from the end of the screw which is closest to the other electrical contacts (i.e., the top rightmost in the image below), e.g., with the tip of a knife, will make establish contact to the body mount again. This made my adapter work and I'm indebted to marvintm whose post "Re: How to fix bad Tamron KA mount" provided me with the solution.

However, since the illustrating images from his post are no longer available, I initially had trouble finding the screws. I finally found them and below is an image showing the location of the screw ends.

Contrary to marvintm's description, the glue on my screw end was not easily discernible by a light blue/green colour. I just lightly scratched on the screw end just in case and the adapter now works like a charm.

Good luck!

P.S.: This explanation of the KA-mount contains all the information required to know for which lens (minimum and maximum f-ratio) the pins should be shorted to the ground by the adapter. This should help troubleshooting if the camera doesn't use the correct aperture range. Note that the adapter does not fully support lenses with a minimum f-ratio slower than f/4 if the maximum f-ratio is f/22 and there is an "AE" setting or f/32 and there is no "AE" setting. Alternative explanations of contacts are Mark Roberts matrix metering mods page and this detailed explanation of the adapter contacts.

P.P.S.: You may want to try to convert a P/K adapter to one that supports P/KA functionality for a specific lens.

[Class A]

The "broken" adapter shows f/4 as max aperture when locked on the camera.

Given that the adapter works as intended when it didn't quite lock yet, I can only assume that it doesn't index properly. Seems hard to fix as well, since you'd have to change the angle/distance between the lens lock hole and the electrical contacts. I ran out of ideas, sorry.

EDIT: As a last resort, you could try to clean the contacts around the spring-loaded "A" contact and check whether they are straight or somehow looked bended. These contacts are referred to as "2" and "5" in the image attached to this post.

[pacerr]

. . . you'd have to change the angle/distance between the lens lock hole and the electrical contacts.

Actually, that's not too hard to do. If you're absolutely sure you have a radial indexing problem, simply elongate the existing latching hole a tiny bit (in the right direction!). Fill in the unused part of the hole with epoxy for a tighter fit.

A 1/32nd - 1/16th inch diamond burr in a Dremel tool works.

However, unless a micrometer measurement compared with a good adapter verifies an out of tolerance condition (very rare), you're probably dealing with a different problem.

H2

[pacerr]

I don't know if this is a fix or just a coincidence. I've got four PK/A adapters (had 'em for a long time, since they were cheap) and have tried many things to solve what appeared to be intermittent faults in the AE mode. Sometimes those "things" seemed to work, but for some stupid reason I never bothered to put a positive ID mark on the rings. They didn't often get swapped from lens to lens when they were working and when they didn't I was too busy swapping parts to keep track.

A few months ago I was messin' about with a ring that wasn't passin' the f-stop data (the F - - symptom) and intentionally engaged the AE mode before mounting the lens to the camera. The lens, which had to be unlocked and rotated slightly to report the f-stop, began working correctly in AE mode.

I now engage the AE mode before mounting AD-2 lenses if I'm using that mode and so far all my adapters are working as they should. After a quarter century of using Adaptall lenses, I don't recall seeing or hearing that tip anywhere before and had always treated the AE mode switch the same way one would use the AE switch on any SMC-A lens.

I don't KNOW that this is a procedural fix, and I'm still waiting for the other coincidental-shoe to fall because I hadn't kept track of other manipulations , but I thought it was time to get some other folks in on the experiment.

If you try this, let us know your results, please.

H2

[Reiner]

Worked like a charm. THANKS!

[BigDave]

This really helped I think. Between this trick and some fiddling I was able to get a ka mount I got used working perfectly!

thanks for the post and keeping it posted!

[i_trax]

excellent post!
yes, I always switch to AE before mounting and regularly clean all contacts with surgical spirt and cotton tips/buds

[arkusnandar]

helpfull post..
thx alot sir..

by the way i have an old dirty SMC-F 35-70mm F.3.5-4.5. the lens have a a lot problem, the optical contain of fungus and the important think the lens cannot using ring 'A' apeture. when i set on 'A' the aperture cannot read in body. my camera is pentax k100D and K20D.
is there anyone help me fixing this lens or maybe have some information how to fix it.

rgd

[ChrisJowett]

Oh my God, thank you!!!!!
I have struggled with my beloved 19AH for months. Just today i put in an ebay bid for a Pentax 70-210 f4 as a replacement option (hope I don't win).
I can't belief a little scratching with a paring knife qualifies as camera repair, but it worked.
Now I'm tempted to have a crack at converting a PK mount for a CW-28. I have access to a Pentax 28mm f2.8 to use a s a template. Should be interesting.

[Transit]

Coincidentally, my auction PK-A arrived in the post this morning.
Nice to have the dear old 90/2.5 back concious in Av
pity about the f/4 max
must read rest of thread
Pete

[fsdogwood]

Well here I am digging this several year old thread out.

Recently got a Adaptall-2 lens, and the pka adapter; after seating the lens firmly to the adapter, now the aperture is displayed on the top LCD and VF, the wheel can change the f value displayed but doesn't seem to have any effect on the lens (i.e., the lens seems to be left at f32). Any suggestion?

TIA

Pinwu

[excanonfd]

Is the lens wide open when it's mounted on the camera (as it should be), or is it closed down to the minimum aperture opening?

[vonBaloney]

And is it actually in the 'AE' position? (You must use little black button on mount to get it in there.)

[excanonfd]

He says he is able to see and adjust the f values with the wheel, which would be impossible without the AE lock engaged.

[vonBaloney]

He says he is able to see and adjust the f values with the wheel, which would be impossible without the AE lock engaged.

Sometimes it will make a weird connection and just display a default aperture even if it isn't controlling anything...

[excanonfd]

Sometimes it will make a weird connection and just display a default aperture even if it isn't controlling anything...

I guess anything is possible, though I've never experienced such phenomenon from any of my PK/A adapters.