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Tamron Adaptall Pentax P-KA auto aperture mount

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8 20,524 Thu October 10, 2019
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100% of reviewers $69.80 8.63
Tamron Adaptall Pentax P-KA auto aperture mount

Tamron Adaptall Pentax P-KA auto aperture mount
Tamron Adaptall Pentax P-KA auto aperture mount
Tamron Adaptall Pentax P-KA auto aperture mount
Tamron Adaptall Pentax P-KA auto aperture mount

Adaptall lenses are of particular interest to Pentax (and Nikon) users because the original mounts fit current DSLR's, with aperture connections to the camera.
The 4 main variants of adaptall mounts to use adaptall lenses on K mount cameras are as follows:
  1. A first generation manual P-KM mount, easily distinguished from the later mount by the lack of a black flange with f numbers on, and only one tab. With this mount you have mechanical aperture connections only. On camera the lenses operate in the same manner as "K" and "M" series manual focus Pentax lenses. PIC 2.
  2. A later/AD-2 PK-M mount with two tabs, this has the black flange with the f numbers on. Also just mechanical aperture connection. PIC 3. NOTE that these latter two mounts offer identical functionality on DSLR.
  3. A P-KA mount with two tabs. This has electrical contacts, a plastic aperture lever guard and no flange with f numbers on. When set on AE/F32 (press the small side button at quarter-after in pic 1 to click into AE/f32 and lock) the lenses operate in the same manner as Pentax "A" series SMC-A lenses: aperture is set on the camera using the speed dial, automatic modes Av, P, Tv can be used and DSLR's will record the F stop in the EXIF data. PIC 1.
  4. Finally, there are also new cloned mounts made in China, these have NO aperture connection and are therefore most like a t-mount. When one of these is used the lens works like a M42 or t-mount lens, all aperture stopping down has to be done manually. However "stop down" aperture priority mode can be used with one of these. The non conductive black paint (on the camera side) means that with most Pentax DSLR's Catch In (trap) focus won't work, and on some the green button won't work. No pic.
The earlier PKM mounts (pics 2, 3) let the lens be used in the same manner as a "K" series SMC or "M" series SMC-M lens. The later PKA mount makes the adaptall lens like an "A" series SMC-A lens.
It is the third, the PKA mount, that is reviewed here.

Mount not working (f numbers not being displayed)? First check that the tabs (ears) are correctly aligned with the spaces on the lens aperture ring, the lens and mount are correctly mated, the mount correctly clicked into f32/AE position. If that all seems correct, try scratching the small screw head nearest to the contacts (circled in PIC 4) on the mount with a knife point/small screwdriver. This is right on the data contact on the camera mount and thread locker can interfere with the electrical connection. Alternatively, cleaning the contacts and/or doing a little gentle wiggling of the lens on the camera can restore proper connection. More in this thread.
Note also that the PKA mounts don't recognise the slow lenses like the 300mm f5.6's, the SP 200-500mm f5.6 (the PKA mounts won't engage into auto mode at all on the 200-500mm f6.9's) correctly: your Pentax DSLR will display f4 (but will otherwise mostly work the same). They also read the f2.5 lenses like the 24mm 01B/BB and 28mm 02B as f2.4, and the f3.8 zooms (03A/103A) as f4. Getting the PKA mount to correctly show f5.6 with the f5.6 lenses is easily accomplished by placing a small piece of insulation between two of the contacts - X pic 4 and see here. Also be aware that a known fault that these are occasionally prone to is that the mount won't allow f numbers below F4. It's not known what causes this.
One possible fault that is potentially hazardous for the camera mechanics is a mount aperture lever that has become bent out of true. In this case the mount will not operate the iris because the lever doesn't properly engage with the camera, or the lever might ride over the mechanism and jam. For reference, the gap between the lever and the lever guard on the mount should be minimum approx 50 thou"/1.25mm.

Discussion of PKA mount exposure inconsistencies:
Part 1;
Part 2;
Part 3.

More info - Stone-G's web page
Scan of original user manual here. - comprehensive overview of most adaptall lenses, and also info on the earlier adaptamatic and t-mount lenses.
Mount Type: Pentax KA
Price History:

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Site Supporter

Registered: November, 2012
Location: North Wales
Posts: 2,068

1 user found this helpful
Lens Review Date: October 10, 2019 I can recommend this lens: Yes | Price: $40.00 | Rating: 8 

Pros: "A" utility
Cons: mechanical and connection glitches, exposure inconsistencies
Camera Used: K-r, K5, K3-ii    Handling: 7    Value: 8   

The first thing is: if you are using adaptall lenses then pretty much you do want one of these. These PKA mounts turn your adaptall lenses into the equivalent of Pentax SMC-A lenses. The most important benefit: on the fly metering in auto Av, Sv, P or Tv modes, no need to press a green button, spin a dial, chimp or guess. And the additional conveniences of aperture adjust using the on-camera dial, aperture data recorded in EXIF.
However these mounts aren't straightforward. The first thing is that everything has to be correct for the mount to function in auto modes in the first place.
  1. Mount correctly engaged and clicked in on the lens. Note that on occasion you may need to press the wee black button on the mount rim to free up the movement of the ears.
  2. Ears correctly engaged in the spaces on the aperture ring. Note that slightly bent ears (quite common with used mounts) may not click into place, and can easily move out of position.
  3. Lens aperture ring properly clicked in to AE/F32 position. Problem? check #1, #2.
  4. Electrical connection good - see "mount not working" in description above. Wiggling and fiddling a bit is commonly required. But usually once the f numbers are displayed on both the rear and top lcd's (must be both), you are good to go.

And 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 Pentax KA mount logic means that F2.5 lenses will 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.


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.
Site Supporter

Registered: May, 2015
Location: Hampshire
Posts: 851
Lens Review Date: June 29, 2016 I can recommend this lens: Yes | Price: None indicated | Rating: 10 

Pros: Better to use than non P-KA adapters, aperture on exif.
Cons: Can require a little work on contacts.

I received my third adapter today, along with a Super A and a Tamron 28-70mm (59A), I like these because I still cannot get used to finding the green button to meter manual lenses with easily.

I bought the bundle as I believed the lens had this P-KA attached...and was not unhappy at getting a Super A (Super Program) along with it, plus the lens though that will probably be sold on. Cost was totalled at approx. $50 including postage at todays poor post exit sterling rate. I'm not the most confident buyer on Ebay but as I have 4 SP lenses and had only 2 adapters, until now, I will not stop until I have enough. Though swapping them is not hard, it is fiddley and I would be happier not to have to.

The first adapter bought was a fluke, it came with a bundle attached to a Tamron 28mm F2.8 which I sold on, having a Vivitar close focus 28mm with A contacts, Sigma 28mm and a Pentax-M 28mm already.

The next two were bought on cameras that the seller presumably didn't realise featured this adapter and would probably made more than double their selling price if they had listed it as such. Both times I got lucky I was able to tell from the images on the listing that the adapter was a P-KA because of the lack of an aperture ring and the small button used to move the aperture to the AE mark. (See image below).

So while I am probably going to reduce my future success rate I recommend anybody wanting one to look closely at the images on listings that look like the seller is just selling off a bundle of old camera equipment.

A note of caution, read the links at the top of the page, my 2nd purchase required taking off the insulation from the screw head as others have had to, thereby getting it to work. Plus there is a detailed explanation on what you need to do to take the adapter off and fit it to another lens.
Site Supporter

Registered: December, 2008
Location: Twin Cities, Minnesota
Posts: 650
Lens Review Date: October 3, 2014 I can recommend this lens: Yes | Price: $40.00 | Rating: 10 

Pros: Allows "A" functions on legacy glass
Cons: can be fussy to mount

I have recently been acquiring these for all my Adaptall lenses. Back when one cost well over a $100 I put it on one of my favorites the 24 f2.5 lens. That one did malfunction but the cleaning corrected it. They can be fussy to mount if you are inexperienced with the adaptall system or have not read the mounting instructions. I was lucky to have my first one come with the Tamron instructions. I never remove them unless I am going to use a teleconverter with the lens and this seems to keep them working. These mount make very good older glass into a much more modern lens. Most of mine are on zooms of various focal lengths and they are all as sharp as any other zooms I own, just not AF. This is an outstanding and unique piece of engineering since I do not believe that Tamron was able to ever make another electrical mount for any other camera brand. I now own 7 excellent examples of Tamron's good lenses from over the years of 80's to 90's. I feel lucky that I have been able to buy them from $45 to $65 in the last few months.

Update as of 9-20-2016:
I now own 5 of these mounts and I have no trouble with them on 4 of the lenses but I discovered that the 24 has a little bit different mounting method. But once mounted it makes that little jewel something my wife likes to use! I am adding to my adpatall-2 collection and may need more in the near future. Ebay has them priced way too high but there are a few private sellers that sell them reasonably. Just bought number 5 for $40.
Site Supporter

Registered: April, 2011
Location: Lost in translation ...
Posts: 17,558

1 user found this helpful
Lens Review Date: March 11, 2012 I can recommend this lens: Yes | Price: None indicated | Rating: 9 

Pros: "A" feature on AD2's and SP's
Cons: Sometimes difficult to engage quickly


I have 2 PK/A's and both work well ... much more prefered as compared to my PK/M mounts. Also works well with the 2x TC (01F). Worth the investment. Used with 103A, 23A, 22A, 02B.

Allez et salut, John le Frog

Veteran Member

Registered: January, 2009
Location: Melbourne Australia
Posts: 2,115
Lens Review Date: August 8, 2011 I can recommend this lens: Yes | Price: None indicated | Rating: 7 

Pros: works with all the adaptall 2 range of lenses
Cons: Occassionally circuitry doesn't talk to the camera and the F stop reading vanishes, fiddly to fit.

I've used this adapter with the Tamron 90 f2.5 macro and the SP300 f2.8 and both have displayed the same annoying trait of occassionally failing to properly connect to the camera body causing over exposed pictures. It is remedied by jiggling the mount but can be annoying when taking pics of living beasties that won't keep still for too long.
As a concept the Adaptall mount is a great idea allowing for one lens to work with many different mounting systems the glitches of the system suggest R+D might have gone a couple of steps further to better refine the product.
Site Supporter

Registered: November, 2010
Location: California
Posts: 2,223
Lens Review Date: April 22, 2011 I can recommend this lens: Yes | Price: $140.00 | Rating: 10 

Pros: Best thing ever after sliced bread - Makes life easier with Adaptall lenses
Cons: A bit too high in price

Nothing to say, I have two PK, one Minolta, three PKA, they make Adaptall lenses work with the A setting. Wonderful complement.
Otis Memorial Pentaxian

Registered: March, 2007
Location: Vancouver (USA)
Posts: 33,950
Lens Review Date: September 27, 2010 I can recommend this lens: Yes | Price: $29.00 | Rating: 6 

Pros: Allows full exposure mode compatibility with crippled AF mount bodies
Cons: A bit fussy in use, not as durable as P/K variant, "Yes" recommendation is qualified by the user finding a good copy
Handling: 8    Value: 4   

I am a real fan of the Tamron Adaptall-2 product line, but am only giving the P/KA adapter a rating of 6 because of poor value at the current market price. My reasoning goes as follows:
  • Current market price (Sept 2010) is often over $100 USD as compared to $15 to $20 USD for the P/K version
  • The aperture coupling mechanism is relatively fragile and somewhat fussy in its implementation. Although mine works fairly well, it has always felt stiff/rough in operation when compared to the Adaptall-2 P/K mount and my other "A" contact lenses.
  • The adapter may be positional on the mount such that a small shift in position may result in loss of "A" contact functionality on my K10D (...yes, I have cleaned the contacts and the screw heads...)
Given that the P/K version delivers excellent results using green button metering in M mode on the K-x and K-7 (and presumably the new K-r and K-5), my suggestion is that high price of the P/KA adapter is not worth the money. As for me, I generally use my P/K adapters in preference to the P/KA and have no intention of selling my P/KA version because of the deficiencies I have noted.

One additional note is that the P/KA adapter lacks the second aperture scale to support the Judas window for viewfinder aperture display on KX, MX, and LX film cameras.

Update 11 March 2018: Since the original review, I have acquired a second copy that works much better. My first copy has been relegated to use as a rear lens cap on a "junk" Tamron zoom. It developed some sort of internal short that led to it being detected as being the the "A" position regardless of where the ring position. This second copy works consistently with no positional issues or need to scrape the contacts. The aperture actuation is also much smoother.

Despite having better luck the second time around, I am still down-rating the P/KA adapter due to poor value in the current market and reported general fussiness by most users. The "Yes" recommendation remains qualified by the user having a good copy.

Moderator Emeritus

Registered: May, 2007
Location: Edmonton Alberta, Canada
Posts: 10,644
Lens Review Date: February 3, 2009 I can recommend this lens: Yes | Price: $100.00 | Rating: 9 

Pros: works well. flexible
Cons: bit of a PITA to mount

This adapter works well for the Adaptall system. The lens attached will give AE controls and all program modes work resulting in a full function lens without auto focus. The only issue (slight) is the adapter is a bit fiddly to attach and detach making it a bit slow to set up. But that feature (removable) makes it possible to have a large number of lenses at a low overall cost.

For more Tamron Adaptall lens info this is an excellent site that lists all the Adaptall 2 lenses that will work with this mount.
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