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08-04-2010, 07:13 PM   #1
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PK/A Adaptall adapter problems...

I just picked-up a nice PK/A adapter from eBay with the intention of using TAv mode with some of my better SP lenses. However to my disappointment, the adapter seems very problematic


The seller told me that he sometimes had to jiggle the adpater to get it to work(after the fact). But I was never able to get it to work.

However... after reading about other peoples experienced, I scraped the screw heads and it began working(so far so good).

Unfortunately... none of my lenses work with anything under f/4.0 and if/when I try to manually meter, the lens doesn't stop down. And if(for example), I try to force it(in M Mode) by adjusting the Aperture to f/5.6 etc, then the moment I take a shot or do anything it falls back to f/4.0 without a warning.

So imo. it feels as though the lens isn't stopping down at all.

Another possible tidbit with regards to the adapter is that the lever that moves the aperture is very very stiff. And I'm thinking that perhaps its to stiff for the camera to actually move properly.

Can anyone comment on this?
Am I the victim of a dud or... is this a common issue with these types of adapters?
Is there anywhere where I could buy these new?

08-04-2010, 07:34 PM   #2
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If the lenses all show F4 you have an open connection in the mount. I had to take mine apart and add a jumper
08-04-2010, 08:10 PM   #3
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QuoteOriginally posted by Lowell Goudge Quote
If the lenses all show F4 you have an open connection in the mount. I had to take mine apart and add a jumper
Sounds interesting... can you explain what this involves? I'd like to have a look, and hopefully have a chance at fixing it.
08-04-2010, 09:08 PM   #4
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QuoteOriginally posted by JohnBee Quote
... can you explain what this involves?
With the lens mating side of the adapter facing up you can see a (usually) white circuit board and one of the two brass rub strips to the left and soldered wires to the right.

Use a soft pencil to mark index lines for re-assembly.

Remove the three larger "Phillips head screws" around the barrel and you can safely access the contacts. Actually, they're JIS (Jap. Ind. Std.) driver heads, not Phillips, but a #00 Phillips works if you're careful -- or even a very small straight bit may do.

Sometimes you can easily identify and adjust a corroded or faulty rub strip. Helps if you have a known good adapter to compare with. Electronic switch contact cleaner may help too.

I don't have my notes handy at the moment, but using an ohm meter/continuity tester and info from Welcome to Bojidar Dimitrov's Pentax K-Mount Page or other Adaptall repair resources on the web (Google it) you can get photos and eventually understand the circuits.

The other common fault is a very slight misalignment of the lens latch pin recess.

Depress the lens release and rotate the lens about one degree as though you were removing it and see if the F-stop reading appears. This can be worked around by drilling out the latch notch for a slightly looser fit. You can re-bush the enlarged notch with epoxy-metal for a tighter fit afterwards if you like.

H2

08-05-2010, 05:15 AM   #5
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QuoteOriginally posted by pacerr Quote
With the lens mating side of the adapter facing up you can see a (usually) white circuit board and one of the two brass rub strips to the left and soldered wires to the right.

Use a soft pencil to mark index lines for re-assembly.

Remove the three larger "Phillips head screws" around the barrel and you can safely access the contacts. Actually, they're JIS (Jap. Ind. Std.) driver heads, not Phillips, but a #00 Phillips works if you're careful -- or even a very small straight bit may do.

Sometimes you can easily identify and adjust a corroded or faulty rub strip. Helps if you have a known good adapter to compare with. Electronic switch contact cleaner may help too.

I don't have my notes handy at the moment, but using an ohm meter/continuity tester and info from Welcome to Bojidar Dimitrov's Pentax K-Mount Page or other Adaptall repair resources on the web (Google it) you can get photos and eventually understand the circuits.

The other common fault is a very slight misalignment of the lens latch pin recess.

Depress the lens release and rotate the lens about one degree as though you were removing it and see if the F-stop reading appears. This can be worked around by drilling out the latch notch for a slightly looser fit. You can re-bush the enlarged notch with epoxy-metal for a tighter fit afterwards if you like.

H2
Hi, thanks very much for the info.
The strips look very good(clean, and it seems to have good contact tension with the wipers). I tested continuity between the strips and the wipers, and it showed good, so I suspect this is not the problem.

Also the adapter seems to line-up with the contact as it display F/## as soon as it locks into place. However, if I adjust it away from the lock position, all display information is lost(so I think it's good that way).

All issues(as far as I can see) seem to revolve around the aperture actuation mechanism, which is very stiff(even to turn by hand). Also all lenses register as as F/4 regardless of what the lens is attached to it(ex: 2.5, 2.8, 3.6). So it seems as though the camera is actually fooled into thinking the aperture changes as the blades never actually move(confirmed through optical preview and stop down metering).

Based on what I've found, I suspect the adapter aperture mechanism is either worn of damaged which impedes the camera's ability to move physically adjust the aperture blades.

Having said all that, it looks as though the f/4 issue is a separate issue from the stiff aperture lever.
08-05-2010, 06:07 AM   #6
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Welcome to the quirky world of Adaptall-2 PK/A shooting, John. Two of mine do the same for no apparent reason. Just go PK-mode and enjoy the ride.

Sometimes I think the PK/A's were built by Lucas Electric (the Prince of Darkness) - if you ever owned an MG you'll understand.

H2
08-05-2010, 07:09 AM   #7
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QuoteOriginally posted by pacerr Quote
Welcome to the quirky world of Adaptall-2 PK/A shooting, John. Two of mine do the same for no apparent reason. Just go PK-mode and enjoy the ride.

Sometimes I think the PK/A's were built by Lucas Electric (the Prince of Darkness) - if you ever owned an MG you'll understand.

H2
What is it about us?

We have a history of owning MG's and (2-wheel and 4-wheel) Triumphs, quirky main-brand camera stuff - and if that isn't enough we have to mess with adaptalls.

Next thing somebody will post something about tube amps.
08-05-2010, 07:25 AM   #8
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just to clarify

what I found with mine, which displayed F4 not the correct aperture, was that while the PCB and the sliders (which perform the encoding of aperture) worked correctly, there was no contact back to the lens mount via the pin in the third location from the lens locking pin. Actually the spring loaded raised contact on the mount and second contact on the lens mount from the locking slot (since one pin location is omitted on the lens side).

The aperture coding works by selectively shorting pins to the lens mount voa this pin. If there is no contact then the displayed aperture is F4.

in looking back at my adapter, i actually put a small short circuit between the slider thatengages the aperture ring on the lens and the mounting screws for the slider which go through to the mount itself, insuring contact all the time

08-05-2010, 07:41 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
i actually put a small short circuit between the slider thatengages the aperture ring on the lens and the mounting screws for the slider which go through to the mount itself
The good news, is I lubed the aperture lever on the adapter and it loosened right up and so stopping down now works(yay for that!).

So it looks like the only issue left is where it display's f/4, however I discovered that f/4 is(in effect) still wide open(visually confirmed) so it looks as though its not a complete catastrophe in the end.

However... I'm very interested in your solution but the instructions I quoted above are still a little difficult for me to understand(I'm a bit of a daft when it comes to written instructions ). So I was wondering if you might think of a way that could help me visualize how you pulled this magnificent feat on your own adapter?

Thanks again to all who are participating with this btw. I really appreciate the help.
08-05-2010, 02:30 PM   #10
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Uhhh, . . .

QuoteOriginally posted by monochrome Quote
Next thing somebody will post something about tube amps.

. . . do ya need a box of slightly used amp and RF tubes?

H2
08-05-2010, 03:31 PM   #11
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John & Lowell

QuoteOriginally posted by JohnBee Quote
So it looks like the only issue left is where it display's f/4, however I discovered that f/4 is(in effect) still wide open(visually confirmed) so it looks as though its not a complete catastrophe in the end.
The problem here is the meter/body interprets the amount of light it "sees" through the "wide open" lens (say, f 2.8) as coming through an f 4 aperture and proceeds to calculate shutter speed vs. aperture ratios on that mistaken assumption. It 'thinks' it's lighter outside than it really is because it's sensing f 2.8-worth of light through what it believes is an f 4 window.

That's why pure manual exposure works in this case and AV doesn't. The camera calculates "match needle" exposure settings based on the actual light passing through what ever aperture you set by balancing speed against ISO for existing conditions. No false assumptions involved and it's re-calculated each time you change any parameter.

QuoteOriginally posted by Lowell:
. . . I actually put a small short circuit between the slider that engages the aperture ring on the lens and the mounting screws for the slider which go through to the mount itself, insuring contact all the time.
I believe I understand what you've done and but I think it would be very useful if you posted a picture of the results to show how you chose to accomplish the "short" - i.e., mechanically or electrically.

But to clarify the results, exactly which aperture reading results from your "constant" contact? I'm presuming the slider is sending actual max aperture of a particular lens and only during AE operation?

H2
08-05-2010, 05:06 PM   #12
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...And that, my friends, is why I prefer my P/K adapters over my P/KA and why I generally recommend the P/K over the P/KA. The actuator on my P/KA has been stiff since the day I bought it new. It works, but I don't really trust it.


Steve
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