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Fixing Tamron Adaptall P/KA Adapter
Posted By: Class A, 02-11-2009, 04:18 AM

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.

Attached Images
 


Last edited by Class A; 09-15-2009 at 06:50 PM.
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09-19-2016, 12:42 PM   #61
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One black tab moves freely off camera, the other one doesn't move at all and pressing the black button has no affect on it whatsoever.

I think what I need is someone close by who can attach this thing to my Tamron 90mm and return it to me fixed. I'm having no luck at all. So, for the time being, I've reattached the one I had on there to start with, the PK adapter.

10-25-2016, 01:02 PM   #62
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QuoteOriginally posted by photolady95 Quote
I'm having no luck at all.
I might have another idea about your stuck PK mount, photolady. Have a look at the small screws that hold on the black ears/tabs that connect with the aperture ring on the lens. Does it look like these have been tampered with or even changed? If a screw of a slightly different length has been used to replace one that has been lost, it can easily cause one of the rings the tab/ear attaches to on the mount to jam. You could try slackening a suspicious screw to see if that frees things up (need ideally 00 JIS screwdriver or similar size cross head may with care suffice).
10-25-2016, 06:13 PM   #63
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QuoteOriginally posted by marcusBMG Quote
might have another idea about your stuck PK mount, photolady. Have a look at the small screws that hold on the black ears/tabs that connect with the aperture ring on the lens. Does it look like these have been tampered with or even changed? If a screw of a slightly different length has been used to replace one that has been lost, it can easily cause one of the rings the tab/ear attaches to on the mount to jam. You could try slackening a suspicious screw to see if that frees things up (need ideally 00 JIS screwdriver or similar size cross head may with care suffice).
Thanks Marcus. I'll try that when I get a set of those screwdrivers. I been meaning to order a set just other things needed more than a set of JIS screwdrivers. I can look at the adapter tomorrow with a magnifying glass to see if they're different though. I'll let you know then what I find.
6 Days Ago - 1 Like   #64
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PKA mounts TEST

Well I decided it was time to empty the box of mounts accumulated over the last year or so and figure out which are the good ones. Turned out I have 17 (15 in the pic, then I found a couple more) - more than I thought!
So I did a bit of structured testing. X-post with PKA reviews page.





Once you have a functioning mount, then the bug is inconsistent exposure results across the f-stop range. This is a bad one:



This is a quite common pattern: underexposure leading to increasing overexposure with higher F stop. This would be consistent with some mechanical "stickiness" in the mount. Pentax cameras operate the iris by holding it wide open, then relaxing that hold to match the set aperture when the shutter is pressed. We can hypothesise that if there are connections that are a bit slow or sticky in the chain camera-mount-lens-iris then the iris simply doesn't close the full amount.
However that's not the whole story by any means, as my qualitative ad hoc test results on 17 x PKA mounts with several different lenses show. I have tried 6 lenses (so far): a 35-80mm f2.8-3.8 01A (used @ 35mm); 28mm f2.5 02B; 90mm f2.5 52B; 300mm f2.8 360B; 35-210mm f3.5-4.2 26A (at both 35mm and 210mm); 28-135mm f4-4.5 28A (at both 28mm and 135mm). These are all adaptall-2 SP's, but I didn't see the need to include eg early adaptall-1's, the design and function of the adaptall mount never changed. All the lenses were tested first with a PKM mount and manual exposure mode to check that exposure results with the lens were relatively consistent. That they might not be was illustrated by a 52BB 90mm I tried initially :



So if you have inconsistent results don't necessarily attribute that to the mount, or only to the mount.
I have simply tabulated the results by hand. Each f-stop column has been divided into 4, this mirrors the dividing lines on the histogram display on the camera. I used a whitewashed wall as subject, this monochrome relatively uniform subject results in a single narrow peak on the histogram, as in the "filmstrips" above. The highlighter line marks the approx position of this peak. The centre line is correct exposure, the lines to L and R are approx -1⅓ and +1⅓ stops respectively.
The second PKA column indicates mount fuctionality.
  1. tick = AOK, mounted and worked;
  2. ! = wiggling/fiddling required but did work. It was noticeable that the 28mm 02B and 35-80mm 01A caused more issues than the other two lenses. Mounts #1, #2, #7 and #15 were pernickety on these lenses but not on the 90mm 52BB or the 300mm 360B.
  3. F4 = couldn't get the mount to show correct F2.5*/F2.8; Mounts 12 and 14 showed the "F4 fault" consistently, although #14 twice went down to f3.5, and with the zooms 28A and 26A showed f5.6. Also mount #6 also refused to show below f3.5 with one lens, the 90mm 52B. In these cases I still went through the same 5 or 6 stop range, F3.5/4/5.6 - F22.
    (*The PKA mount logic means that F2.5 lenses show as F2.4, this affects the 02B, 52B in this test and also lenses like the elicar 90mm f2.5, vivitar 105mm F2.5. See note 1 below.)
    F4 fix - see note 2 below.
  4. X = didn't work. Mount 4 proved non-functional (surprisingly, I'm sure I had it working previously, however nothing I tried, including re-scratching the screw head, worked).
The camera , a K3-ii, was set on Av, 100, 200 or 400ASA, default multi-segment metering, no exposure compensation, JPG - XS. One point to bear in mind is that the camera doesn't adjust the shutter speed steplessly but in steps of 1/3 stop (as per camera settings).
Charts: click on the link or on the chart to view 1250px sized.

Control: 4 x PKA mount lenses. SMC-A 50mm f1.7; Vivitar 28mm F2; Elicar 90mm F2.5; Vivitar 105mm F2.5. My K3-ii demonstrated almost perfectly consistent exposures F1.7-16 with the SMC-A 50mm, good consistency with the vivitar 105mm, vivitar 28mm, the elicar 90mm was consistent through middle stops but showed large underexposure.

Click on a chart to pull up large.

















Observations:

1. My K3 underexposed initially (min F) with all the adaptall lens+mount combinations. Only slightly with the 02B, by almost a stop with the 360B. And the "F4" mounts #12, #14 underexposed by more, though I can't think of a reason why they would, or why there is a significant discrepancy between 01A + 02B and 360B + 52B, and between wide angle and telephoto with 28A and 26A.






The discrepancies between the two sets of results with each of the zooms 26A and 28A adds a frustrating extra variable to the use of these mounts.

2. Then first stop down there was a correction to, or near to, correct exposure with a majority of the mounts. This is most noticeable with the 52B and the 360B because the initial underexposure was significant with these two lenses. With 52B half the mounts jumped to near correct exposure, with 360B just about all the mounts moved near correct exposure, though the "F4" mounts #12, 14 were still showing underexposure. From this point, the "good" mounts would be pretty consistent with only relatively small + or - variances through to F11. Mounts which tended to vary more would show gradually increasing overexposure through to f11. Mount #3 above was the worst, mount #16 also showed this pattern, while mount #9 was one of the best:




3. Exposure variance did tend to increase with f stop, and most notably from F11 to F16. Mostly a jump to overexposure, but also in a couple of cases (mount #8 especially) a jump back to underexposure! Why mount 8 might do that is unclear.

4. Each PKA mount exhibited a broadly consistent pattern of exposure with each of the test lenses.

5. The mounts showed clearly bigger exposure variances with the 28mm 02B, and the least with the 300mm 360B and the 35-80mm 01A. So the lens can certainly be a significant factor.
So what can we conclude from all this? First: be aware of these inconsistencies. It's clear to me this is the nature of the beast. Check out your mount(s), familiarise yourself with how they perform and factor in exposure compensation accordingly. Second: wide open may not be the best f-stop to set exposure compensation from. With many, or even most, of these mounts that would be better done chimping one stop down (unless you are taking pics at wide open aperture), then the mounts are most consistent through those middle F stops. Finally, it's well worth IMO shopping around for PKA mounts, checking them out and when you find a good one, keep it! And the "F4" mounts are perfectly usable, particularly so with lenses like the 300mm f5.6 54B, 200-500mm f5.6 31A, with which the f4 issue doesn't matter (see link above in the description for how to get the mounts to read f5.6)

6. I also checked to see if a different metering mode made any difference, specifically to the initial wide open metering, it didn't. Also whether bright light/high ISO fast shutter speeds vs low light slow shutter speeds made any difference in the response of the mount + lens combo, but, broadly speaking, I didn't notice anything significant.


Note 1. Does the erroneous F2.4 with F2.5 lenses cause exposure error of around an eighth of a stop? On reflection, I don't think so. Two opposite things happen that cancel out. The camera registers the F2.5 lens as F2.4. Then, when you set the aperture to eg F4, the camera (in an auto mode) adjusts the shutter speed to compensate, assuming the base is F2.4. This adjustment will therefore be that 1/8 stop more ie slower than it should be. However the camera also calculates the movement of the iris from this same base. The closing of the iris will be ~ 1/8 stop more than it should be, causing an underexposure that cancels the overexposure from the slower shutter speed. So the net effect on exposure is ~ nil, but you will actually be at ~F4.15.
Note 2. I spent some time afterwards disassembling and inspecting the "F4" mounts 12 and 14, mount 3 (overexposure) and mount 4 (not working). I was able to fix mount 12 by fiddling/bending to improve the connection of the internal moving contact E, but mount 14 still wouldn't go past f3.5. I could not identify any particular reason for mount 3 overexposure. My tentative hypothesis is that the PKA mount may not be engineered well enough, it is easy to flex the aperture actuation levers ends by touch, flexion (or some looseness) under the implulse forces of shutter release could cause the observed inconsistencies. And as for mount 4 I probably need to fault trace the internal circuitry with a continuity tester.



Last edited by marcusBMG; 4 Days Ago at 06:23 AM. Reason: added observation 6
6 Days Ago   #65
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I have one where it seems to mount ok and the f stop shows on the LCD,etc, but aperture closes super slow. When unmounted lever moves freely, seems just as springy as any. Can't figure that one out.
6 Days Ago   #66
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QuoteOriginally posted by vonBaloney Quote
Can't figure that one out.
I have a PKA with a similar behavior. It appears to be due to friction binding in the aperture actuator linkage.


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6 Days Ago   #67
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As I remarked in the write up I have not been able to attribute a cause to the profile of eg mount 3, and I have had a number of these opened up for inspection, testing screw and mounting tightness, the movement of parts etc etc. I am not an engineer with an engineering set up to try to test if there are inherent inaccuracies/flexions/issues in the mechanical train. i do note that the leverage factors suggest that it wouldnt take much to produce such results.

Note that #3 was the worst case. Other ones had some similarity but half/more than half of the mounts (depending on lens) were actually pretty, or even very satisfactorily, consistent one stop down through to f11 eg mounts 1, 7, 9, 10, 15 16, 17.

Last edited by marcusBMG; 6 Days Ago at 04:43 AM.
6 Days Ago   #68
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Thank you for the update, I use few PK-A and not all are perfect. I was able to fix one, but maybe I will re-check another which works only partly as expected.

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