Takumar Tales: Pentax 55s - Unsung, Yet So, So Good

"The Planar Killer."

    "It nearly bankrupted Asahi (Pentax)."

    "The Holy Grail of 50mm lenses."

     Three phrases that have never been applied to the unheralded, yet best-selling, Pentax 55/1.8 and f/2 "normal" lenses ;-). But these humble optics did more to establish Pentax' reputation as a purveyor of fine cameras and optics during the 1960s than any other. No, it wasn't through bold (if debatable) statements applied to the lovely, but now relatively scarce, 8-element Super Takumar 50/1.4 released with the Spotmatic in 1964. (Which was quickly replaced in 1965 with a 7-element version using "rare-earth", thorium-treated,  glass to achieve even better performance). Rather, it was through understated, sustained excellence. First introduced in 1958 & 1959 in plain Takumar and Auto Takumar forms, respectively, the 55/1.8 (and its budget twin, the 55/2) would maintain their basic optical formula (albeit with adjustments to the glass types and coatings) through multiple variants, culminating in early K-mount versions, for a two-decade run on the market. So what was so special about these ordinary lenses?   

  Origins

    The 55 1.8/2 Takumars did not come out of a vacuum. Instead they were improved versions of the earliest M42-mount 55mm lens conceived at Asahi Optical Co. (which would come to be known colloquially in the years ahead as Pentax, after their very influential, pentaprism-equipped SLR that debuted in 1957). The original standard lens kitted with the Pentax was (wait for it...) a 55mm f/2.2 plain Takumar ("plain" referring to the fully manual pre-set aperture system and 'Takumar' named after Asahi's founder Kumao Kajiwara's brother, Takuma) made up of 5 elements in 5 groups. Within months, the optical designers at Asahi had added another element (making the existing concave fourth element thinner, and cementing a new convex fifth element to it), also adding a semi-automatic aperture mechanism, thus birthing the first Auto Takumar (also a 55/2.2). The resulting 6e/5g formula became the template for all succeeding 55mm Asahi/Pentax lenses, and was quickly adapted into f/2 and f/1.8 versions during 1958. The f/2.2 would survive until 1963, when it was decided that there was no need for three moderate-aperture 55mms in the lineup. Just to muddy up things a little more: on re-badged Sears versions of the Pentax K (1958-59) labelled as "Tower 29" in the USA, the first Auto Takumar 55/1.8 was badged as an f/1.9 lens, but was identical in reality ;-). In summary, by 1964, there would be two 55mm Pentax lenses (in f/1.8 and f/2 flavors) and they shared identical optics. The only difference being the addition of a field stop to limit the maximum aperture to f/2 instead of f/1.8 on the 55/2, which was used as a kit lens on the budget Pentax SLRs while the 55/1.8 was standard equipment for the Spotmatic and SL models (the Spotmatic could also be had with the 50/1.4 as a kit lens).  

6-element in 5 groups optical layout that was used for two decades by Pentax for its 55mm lenses

    Why a 55mm focal length versus the standard 50mm used by rangefinders since the introduction of the Leica? Because at this early stage in SLR development, that extra 5mm of focal length made achieving sufficient back focus required by the reflex mirror easier to achieve. Double Gauss development would be rapid through the 1960s and soon 50mm was back as the standard focal length, but Pentax would stick with the 55s simply because they were that good. They would not make the jump to a 50/1.7 until the release of the M-series of compact SLRs along with their correspondingly-sized optics in 1976. We will confine ourselves in this article to the versions with automatic aperture operation as they are the lenses you will most likely encounter. 

​  A Who's-Who of the 55/1.8 & 2s

   1960-65 

    55/1.8 Auto-Takumar (Product # 345; Introduced in 1960) - Although labelled as an "Auto"-Takumar (which originally denoted a semi-automatic aperture), this 55/1.8 was actually the first of what came to called "Super"-Takumars (Super = fully automatic aperture), with the aperture ring re-located to the rear of the lens instead of the front. Automatic here refers to the stopping down of the aperture before exposure and the subsequent re-opening of the aperture following exposure. Semi-automatic apertures closed down automatically when the shutter release was pushed, but required the user to advance the film to re-open the aperture for the next exposure...thus semi-automatic operation. The 55/1.8 Auto-Takumar (and all subsequent Super Takumars) automatically re-opened the aperture immediately following exposure, eliminating the step of re-opening the aperture via film advance. The optics of this lens were unchanged from the previous Auto-Takumar version. In a weird switch, the aperture ring labelling and operation were reversed from standard Pentax practice with the values increasing from left-to-right (a la Leitz, Canon, & Minolta) instead of right-to-left (a la Zeiss, Nikon, and all Takumars heretofore). The movement of the A/M lever was also reversed to match the aperture ring. Discontinued Oct. 1962. 

    55/1.8 Super-Takumar (Product # 345-2 Introduced Oct. 1962) - Identical to the Product # 345 except that it was now labelled as a Super-Takumar, as it should have been all along. On late-production copies, the focus ring now had a scalloped grip versus the flat grip of the previous version. Discontinued Oct. 1963.

    55/2 Super-Takumar (Product # 345-3; Introduced in 1962) - Identical to the Model # 345-2, apart from the field-stop which restricted the maximum aperture to f/2, and it also retained the flat-grip focus ring of the Model # 345 (at least until the stock of flat-grips was exhausted). "1.2/55" and aperture ring digits are butter-yellow in color. Coatings now were pink/blue instead of purple/blue. Discontinued Oct. 1963.

    55/1.8 Super-Takumar (Product # 345-5; Introduced Oct. 1963; # 34550 from Oct. 1966-on) - Aperture ring markings were now returned to standard Takumar practice (increasing from right-to-left), as did operation of the A/M lever. The scalloped focus ring was carried over from late 345-2 production.    

    ​55/2 Super-Takumar (Product # 345-6; Introduced Oct. 1963) - All of the same changes that were applied to the 55/1.8: aperture ring, A/M lever, and the scalloped focus ring. Discontinued 1966.

  ​1965-77

    55/1.8 Super-Takumar (Product # 371 Introduced in 1965; Product # 37100 from Oct. 1966-on; # 37101 from Apr. 1971) - Although looking almost identical to the preceding 345-5 version, save for a scalloped aperture ring that now mirrored the pattern of the focus ring, this lens received a major internal update. In concert with the new 7-element 50/1.4 Super-Takumar, the 55/1.8 was now utilizing glass that included "rare-earth" i.e.  radioactive (in this case, thorium dioxide) additives. This would be a major trend among the Japanese optics manufacturers for the next decade or so. The reason: a major boost in the refractive index of the optical glass along with lower dispersion, which led to better optical performance. The appeal of thorium-treated glass was that it presented a lot of bang for the buck. Case in point: by adopting such glass for the 7-element 50/1.4 Super Takumar, Pentax was able to equal and even exceed the optical performance of the previous 8-element version that required more material and labor to produce. Using about 2/3s the concentration of thorium in the 55/1.8 as they did in the 50/1.4 still made for a marked increase in optical performance over earlier versions. We will dig more into the advantages and drawbacks of lenses containing thorium later ;-). The optical coatings changed from blue to purple. The 37101 was a late version fitted with meter-coupling pins (but no multicoating) to function with the ES model introduced in 1971. Confusingly, Pentax used this same product number for the first Super-Multi-Coated version of this lens that had NO meter-coupling pins but DID have multicoating (face meet palm ;-)). Discontinued 1972.

Cutaway view of the # 37100 lens showing the beautiful mechanical and optical contruction of the Super Takumars

​    55/2 Super-Takumar (Product # 37102 Introduced in Oct. 1966; # 37103 from Aug. 1967-on) - Same changes as the Model # 37100. The #37103 brought a change of markings from A/M to AUTO/MAN. on the stop-down lever. Discontinued 1974.

    55/1.8 Super-Takumar (Product # 37106 Introduced in 1971) - Late-production Super-Takumar that was equipped with light-meter coupling pins for use with the new Electro-Spotmatic (ES) SLR. This made it mechanically-identical to the upcoming Super-Multi-Coated Takumar, but without the multicoating. Japanese market only.

    55/2 Super-Takumar (Product # 37107 Introduced in 1971) - Same upgrade as the 37106. 37107 is engraved on the back of of the AUTO/MAN. lever.

    55/1.8 Super-Multi-Coated Takumar (Product # 37101 Introduced in 1971; # 37104 from Sept. 1971-on; #37106) - Here the waters get a bit muddy as Pentax began another major transition: this time to multicoating and meter-coupling, and not necessarily in the same order on all lenses ;-). The 37101 had no meter coupling pins, but was multicoated. The 37104 had meter coupling pins AND multicoating. The 37106 was a Japanese-market-only lens with minor internal changes from the 37104. Clear as mud? Perfect ;-). Discontinued 1972.

    55/1.8 SMC TAKUMAR (Product # 37108 Introduced 1972) - The first major exterior re-styling in a decade. The focus ring grip was now a waffle-pattern rubber and the aperture ring had coarse, straight knurling. Internally, the lens was identical to the previous version. Another possible major update: Very late copies also reportedly received revised optical glass that eliminated the thorium content, with no loss of performance. Such an introduction of a feature from an upcoming generation of lenses, would fit with Pentax' previous behavior with prior generations of these lenses, so I would call this plausible, but I have yet to see hard evidence to prove it :-). Discontinued 1975.

    55/2 SMC TAKUMAR (Product # 37109 Introduced in 1974) - Same updates as the 37108. Discontinued 1977.

Final version of the SMC Takumar 55/2 mounted on the SP1000

    Even though they are not labelled as Takumars, there are two final versions that qualify in my books, seeing as they are optically identical to the last of the SMC Takumars: the SMC PENTAX K-mount models introduced in 1975 with the K-mount SLRs. Along with the change of mount and cosmetics, there was one other major change: the elimination of thorium dioxide from the glass = no more radioactivity. The 55/1.8 could be kitted with the K2, KX, and KM and the 55/2 was paired with the first run of K1000s (introduced a year after the three other K-model SLRS). 1977 would see the end of the 55s...truly, the end of an era.  

Same optical design...same great build quality...but now a Takumar only in spirit ;-)

  The Elephant in the Room - Radioactive Lenses

    A large proportion of the 55mm Taks (manufactured from 1965-75, approximately) contained rear elements that had thorium dioxide added to increase the refractive index and lower dispersion of the glass to improve performance. Many other manufacturers also made use of thorium during that same period to achieve the same objective (pun intended ;-)). Without getting too far into the weeds (and also getting into a debate about personal views regarding radioactivity :-)), there were both advantages and consequences to its use.

    An obvious and immediate advantage was higher optical performance for very little financial outlay (thorium is a common byproduct of the uranium refining process, which increased exponentially in the post-WWII period, driving costs down). The optical downside is the fact that over decades of non-use (which the majority of these lenses experienced) a byproduct of thorium decay is "yellowing", or more correctly, "browning" of the thoriated elements (usually most noticeable in the center of the affected element(s), with a concurrent loss of light transmission. This can, however, be reversed by exposing the lens to UV light, thus restoring optical performance. 

    A second disadvantage (for some people), is the fact that these lenses are radioactive. This is very much a matter of personal preference :-), as for some individuals any amount of radioactivity is too much. For others, it is not an issue, as the amount of exposure with one of these lenses mounted on an SLR for two hours is roughly comparable to having a chest X-ray performed, or making five consecutive transcontinental (using North America as an example) flights, things we rarely, if ever, contemplate as jeopardizing our health. Again, this is a matter for personal decision, so do your research and determine for yourself your own threshold of risk. There is also a simple solution if you determine that you do not want to have anything to do with thorium-fortified lenses: get a K-mount version. No radioactivity and all of the optical performance, as standard optical glasses had also been improved in the intervening decade after the thorium Super Taks debuted.

   The greatest risk of radioactive exposure with these lenses was actually during production when the glass was being made, with the brunt being borne by the workers adding the thorium dioxide to the molten glass in the crucibles. And this issue was likely a large reason for the almost complete abandonment of thorium in Japanese lens production by the mid-'70s, over two decades before it was officially banned in 1999. The risk of future litigation could have been a major motivation as companies in Japan saw what happened to the Showa-Denko corporation in 1971, and the Chisso corporation in 1973, for their culpability in the propagation of Minimata disease due to decades of chemical dumping. Together with the improvements in standard types of optical glass by the middle of the decade and the easier availability of alternatives such as lanthanum oxide (1/10,000th the level of radioactivity of thorium), the benefits of using thorium dioxide in optical glass versus the drawbacks were basically negated, at that time.

  Using the Pentax 55/1.8 and 55/2 Lenses

    Optics aside, these lenses (both Takumar and K-Series) feature beautiful build quality and are a pleasure to use. Focusing is silky-smooth with aluminum-on-brass helicoids, the knurling of the focus and aperture rings is beyond reproach on metal grip versions, and the resulting tactile experience is all the more amazing given the prices these lenses are still available for nowadays. But that's just the cherry on top: you will be hard-pressed to find anything that exceeds their optical performance in the nifty-fifty (f/1.7 - f/2) category from the era. They pack a bit more outright resolution than the famed 50/1.4 Super-Taks (take your pick from the 7 or 8-element versions, it doesn't matter) while still giving delightful out-of-focus performance that catches most users by surprise when they try one for the first time. If you are into reversing your normal lenses for close-up use, these are also a better choice than the f/1.4s. I have run a K 55/1.8 reversed on my Nikon D300 (sacrilege, I know ;-)) with superb results. It is easily done, as Pentax seemingly arbitrarily changed the filter ring diameter to 52mm (same as Nikon's standard lenses back then) for the SMC Pentax series, before reverting back to their familiar 49mm with the second-gen K-mount SMC-M lenses (the 55 Ks were killed off and replaced by new 50/1.7 & 2 M lenses, at that time, unfortunately). 

    Of course, that is not to say they are "perfect". Vignetting and softer corners wide open are par for the course, but from f/4 to f/11, you will not find better performance from any comparable lens from their heyday. They will easily keep up with modern digital sensors past 24MP at those apertures. Using M42 or K versions on mirrorless digital ILCs (interchangeable lens cameras) is a mere adapter away :-). M42 versions can also be adapted to K-mount SLRs and DSLRs with Pentax' M42 to K-mount adapter, although the cost for genuine copies of the adapter has gotten increasingly ridiculous due to its scarcity, nowadays.  

    For my money, the K-versions are the pick of the litter:

• All of the optical and build quality of the M42s.
• You don't even have to think about radioactivity.
• They are just as easily adapted for mirrorless, if that is your bag.
• There are still a slew of K-mount SLRs available that they work perfectly on.
• They are also usable on several Pentax DSLRs, albeit with some exposure niggles. 

​
    However, if you are a dyed-in-the-wool M42 user, you will not be disappointed with any of the Super Taks, provided the copy is in proper condition. My personal pick would be a very late SMC Takumar as they have the best coatings of the M42s and could possibly also feature non-radioactive glass, as it was Pentax' custom to introduce new features on very late versions of generations that were about to be replaced as a sort of beta-testing procedure. I have not yet come across one of these personally to verify the reports of non-radioactivity, so I cannot say that this is conclusive.   

  Wrap-Up

    My K 55/1.8 remains my favorite Pentax lens. Sure, there are other lenses that Pentax made that better it in some, if not all, technical respects. But it just feels right, not only in actual use on a K-mount SLR, but also in the feel of the images it produces. The first time I used it was at a local conservatory. When I got the images back, it wasn't that the lens had somehow vaulted my photographic capability into the stratosphere (far from it ;-)), but I immediately got the same feeling of the place I had been. The colors...the way the bokeh rendered...I swear it recorded the smells ;-). In other words...it matched my memory. I can think of no higher complement for a lens than that :-).

  References:

    The Definitive ASAHI PENTAX Collector's Guide 1952-1977 by Gerjan van Oosten
    ASAHI PENTAX Lenses & Accessories Brochure c.1966
    Honeywell Pentax Product Catalog - 1973-07
    Various Pentax Brochures & Manuals @ https://www.pacificrimcamera.com
    Pentax Lens Reviews @ https://www.pentaxforums.com/lensreviews/