Review: Adaptall-2 System Custom Mount for Pentax A

(03 December 2010)


I sort of thought that I would never sacrifice the money required to get a Tamron PKA adapter for my vintage Adaptall-2 lenses. After all, I have been a happy user of the common, completely manual PK adapter since 1982 and current prices - during 2010 ususally around GBP 60 - on e-Bay seemed rather exorbitant for a simple piece of metal with four electrical contacts. (The PK-M adapter typically sells, in 2010, for GBP 20-30 on e-Bay, and you shouldn't need be prepared to pay more than that).


But then came this auction for a Tamron 200mm f/3.5 Model 04B that had been on my wish-list for a long time ---- and there was an intriguing picture too:

There was absolutely no specific mentioning on the mount other than that the seller said, he had no knowledge of cameras and lenses and, therefore(!) included a picture of the mount. So, why not give it a try? To make a long story short, I won the auction in competition with just one other bidder at a winning bid of GBP 54 including postage. Since Model 04B typically goes for around GBP 30, one could either say that I got an Adaptall-2 PKA mount for GBP 20 which would be GBP 40 below current market prices - or you could say that I got the PKA mount for 10 GBP below market value and in addtion the 04B lens for absolutely free. Under all circumstances a good bargain ----- if the PKA mount worked, (rememeber there was no mentioning or guarantees about this mount in the ad).

Well, it did work.....

....and today I have three of these mounts so, clearly for me, these things are dangerously addictive. And here's just a little about how and why:

Some common(?) problems:

The Tamron PKA mounts do not have the very best reputation for reliability and stability. If you search the net, you will find, that quite a few have experienced electrical contact problems, some times solving these by scratching the rightmost screw to the (smaller) of the four electrical contacts seen on the pictures above. I have never experienced this kind of problems myself and sometimes wonder, if all users are treating the mount in strict accordance with the manual, (see link at bottom of page). I believe it is essential to follow the instruction that aperture should be set at maximum opening (lowest f-number) when attaching and dismounting the mount to the lens. On the other hand, others who like me have more than one mount have mixed experiences, and there may indeed be an insulation problem with some of the mounts out there. So, if you buy, do check that the seller guarantees "full functionality".


Another problem may be decibed as "occasional loose connections" which I do experience sometimes myself: The camera does not reckognize the lens as an A-lens when the lens is set in AE-position - the setting that allows operation of the lens with the camera in automatic mode(s). But this is a minor, trivial problem: Just releasing and turning the lens back again always solves that problem for me.


One final problem can be described as "too small maximum aperture setting". And that problem, I know of myself. The second mount that I bought (also on e-Bay - for GBP 40)stubbornly refuses to allow aperture settings below f/4 and that is irrespective of whether I use the lens in manual, program, aperture priority or shutter priority mode. The third and last that I bought on e-Bay (a recent buy-now purchase for GBP 60, November 2010) as well as the first one bought together with the 04B lens do not exhibit this kind of problem. They both go nicely down to but not lower than f/2.8 on my 01A lens to f/2.4 on my 01B lens and to f/3.5 on my 04B lens.


So, I should have returned the second mount and requested a refund - but I did not, and for reasons that will become evident below, I am happy that I didn't.


Some general limitations:

There are two fundamental constraints with the use of Adatall-2 PKA mounts:


1. Minimum aperture applicable

While most Tamron Adaptall-2 lenses have a minimum aperture of f/32, this minlmum aperture of f/32 cannot be used with any Pentax camera (analogue or digital) in any mode (M, Av, Tv, Sv or P). The position of f/32 on an Adaptall-2 lens with PKA-adapter serves as AE position only.


Thus, if you do want to use your lens af f/32 you will have to use the PK-M adapter, which will then work in M-mode only. However, since my experience with all my Adaptall-2 lenses is, that optimum performance lies in the range from f-numbers around 22 and lower, I do not really feel this as a severe limitation.


2. Underexposure risk with Adaptall-2 lenses slower than f/4.5

When using Tamron lenses with a maximum aperture of f/4.5 or slower in the Program, Sensitivity or Shutter-priority mode (P, Sv, Tv) the camera may "believe" that aperture settings below f/4.5 are feasible and thus, underexposure may result (ususally in low-light situations).


One will see this happen as the indicated "apparent" aperture value in the viewfinder and/or on the top LCD-display is larger (smaller f-number) than the actual available maximum aperture value (f/4.5 or slower). In such cases one will have to operate the camera in manual or aperture priority mode (M or Av on Pentax cameras). In my user's manual (see link below) it is stated that this only applies for the SP 200-500mm f/5.6 Model 31A. However, this tells me that the manual that I have was written after 1984 when my SP 300mm f/5.6 Model 54B was phased out, because exactly the same thing applies to this model. And I am pretty sure it applies to model 06A (f/6.9 system released in 1985) also.


Note: These lconstraints are due to what one might call "limited compatibility between Pentax-A and Tamron Adaptall-2 lenses' contact patterns". The "standard reference page" for a detailed discussion of this limitation is Bojidar Dimitrov's Pentax K-mount Page: Features and Operation of the KA Mount


Now this is where my defect PKA adapter mentioned above comes in: Because it will never allow settings - apparent or real - of wider aperture than f/4, I can use it with my Model 54B without much concern in all modes. In the cases where the camera automatics calculates exposure based upon an "assumed" aperure of f/4 rather than the actual f/5.6 that will be used, I will get a slight underexposure but no more than can easily be salvaged by some gentle post processing - if at all required. Thus, I have this defect adapter permanently mounted on this particular lens and walk around happily, using any mode as the situations call for.


A few other links on PKA-issues:

PentaxForums: Fixing Tamron Adaptall P/KA Mount

PentaxForums: Adaptall PKA adapter works on K100D, not so well on K20D?


My experiences:

So, I got myself some fairly primitive metal rings with some electric contact patterns - purchased at some horrific prices on e-Bay. Their current selling prices equal or exceed the prices for many a good quality Tamron apaptall-2 lens of that area. Are they worth it, then? Well, to me they are!


I photograph a lot with vintage MF-lenses of the 1970'ies and -80'ies; not just for the sake of trying - in a sense this IS my photographic hobby. For a great many years, I was only using entirely manual lenses (on my trusty and fully manual Pentax K1000 which is still fully operational today without having ever needed repair or service since I bought it in 1982).


So, what's the big deal about having Pentax-A functionality - without autofocus - now, some 25 years after the Pentax A-lenses emerged? Well, to me, it simply means more successfull and better pictures!


It is a tremendous virtue of Pentax that they have preserved backward compatibility all the way to their SMC-M lenses - and even to the M42 mount, if you can live with stop-down metering. And in priciple, it is very easy to get the correct exposure: Just selct your aperture, press a button ("the green button") for light metering and the camera comutes the proper exposure time for you and you may the confidently press the shutter release. But whenever speed is of essence (action, children, insects.....), I tend to forget to press that green button, or I loose prescious fractions of a seccond before I can press the shutter release. Here's where A-functionality counts: I can concentrate exclusively on maintaining focus. And manual focusing is in many instances - depending on available light and lens quality, of course - as fast as autofocus. Who hasn't tried an autofocus that hunts for ages in less than perfect lightening condition???


And further, one is not constrained to working in M- or Av mode only. The Adaptall-2 PKA mount also permits operation in P, Tv and Sv Pentax modes. This adds greatly to the versatility of the system. And with the Tamron SP 140F, 01F and 200F teleconverters you will have the same functionalities preserved


There is an added benefit too: You get full EXIF data (apart from focal length, which one must enter manually in the (Pentax in-camera) Shake Reduction routines). This is very valuable for later evaluation of one's achievements - in particular in connection with special disciplines such as astro- and macro photography. And if you are into HDR-photography it would normally also be a requirement that there is full EXIF data for sensitivity, exposure time and f-number for the software to produce proper results.


Thus, vintage lenses with A-functionality have a lot to offer even in the digital era. A modern quality lens may easily cost, say, 800 - 1500 EURO (at least where I live). I can get some 10-15 quality vintage lenses for that money --- well, not genuine Pentax-A lenses of that time as they are horribly expesive today too, but Tamrons and certain other third-party lenses that were and are small design master pieces in their own right.


Granted, these vintage lenses may rarely be fully as good as their modern conterparts, but then, for the same money, I get a much wider pallette of optics with which I may actually take some pretty varied and pretty good pictures...........


.......and then there is of course the simple, plain fun of using and "keeping alive" those old craftsmen-designed and -built lenses.



Tamron Adatall-2 200 mm f/3.5 (Model 04B)

Pentax K200D in Aperture Priority (Av) Mode

ISO 200

1/90 sec @ f/6.7




Brochure: Tamron Adaptall-2 Custom Mount for PKA (adapted from complete user's manual)



Copyright 2010 - Steen G. Bruun