Data sheet: SMC Pentax-M 50 mm f/1.4

Pekka Buttler, 06/2023


The table below summarizes the lens’ key specifications (measurements are based on the pictured sample):

Brand:Asahi Opt.Co. (Pentax)Lens nameSMC Pentax-M 1:1,4 50 mm
Focal length(s)150 mmAngle-of-view247 °
Maximum Aperturef/1.4In Production1977–1984
Lens mountsPentax KSubfamily (if applicable)––
Length337,1 mmDiameter463,0 mm
Filter ring diameter49 mmWeight236 grams
Lens element count7Lens group count6
Aperture blades (S/R/C)58 SFocus throw200 °
Minimum focusing distance45 cmsMaximum magnification1:6,9
Has manual aperture ringYESHas Manual focus ringYES

Further notes:
• This lens is part of a long and highly distinguished lineup of lenses, starting in 1964 continuing even today. See version history below.
• NOTE! This lens has featured in a JAPB comparison of fast fifties. See here for details.

History of Asahi / Pentax

The camera business today known Pentax was founded in 1919 as Asahi Kogaku Kogyo (Asahi Optical Company). Initially the company manufactured lenses for eyeglasses, later diversifying into projection lenses and even later into photographic lenses, supplying lenses for camera makers such as Konishiroku (Konica) and Molta (Minolta) and binoculars.

In 1952 – the year of the Helsinki olympiad – Asahi released the Asahiflex, the first Japanese 35 mm SLR. Together with its SLR cameras, Asahi introduced a line of lenses that carried the name ‘Takumar’, in honour of the founder’s brother.

In 1975 Asahi/Pentax introduced its own bayonet mount – The Pentax K mount – and phased out the production of m42 lenses and cameras. The name Takumar would remain on Pentax lenses until 1979 (and made some sporadic reappearances). The Pentax K mount is still a current mount, but it has several versions/generations. For details, see the JAPB article on the Pentax K mount.

Pentax was among the handful of Japanese camera manufacturers to keep up with the introduction of autofocus SLR cameras, and even survived the shift from film SLRs to digital SLRs (albeit somewhat struggling).

History of the 50 mm f/1.4

The 50 mm f/1.4 lens has a very special significance to Asahi/Pentax. At the end of the 1950s Asahi/Pentax already was a successful camera company, but back then Japanese products were still often considered to be budget options and poor copies of American (in the case of e.g. cars) or German (in the case of optical equipment) products. Japanese companies were seen very similarly as we only recently viewed Chinese companies: only able to emulate, not to innovate.

This was also back when really bright (brighter than f/1.8) standard lenses on SLRs were still quite rare and often struggled mightily. Such lenses typically were forced be a bit longer than standard (> 50 mm) and often also were only limitedly usable wide open. The lens designers at Asahi set their sights on showcasing Japanese innovation prowess by doing what companies such as Zeiss and Leica had theretofore failed to do: design and produce a 50 mm f/1.4 lens that one would use wide open happily.

This goal they did achieve in the form of the 8-element 50 mm f/1.4 Super-Takumar (1964) – a lens that employed an extra element, turning the customary double-glass doublet group into a triplet to achieve a first: A 50 mm f/1.4 SLR lens that was actually usable wide open.

This original 8-element design has since garnered a number of nicknames, most of which are variations on ‘Planar killer’ (in reference to the Carl Zeiss Planar 55 mm f/1.4 – the lens to beat). While an undoubtable tour-de-force of Japanese lens design and manufacture, the lens was so hideously difficult and expensive (rare-earth elements in glass mixtures, large cemented triplet) to manufacture that Asahi/Pentax lost money on each lens they sold. in 1965 Asahi managed to come up with a lens of similar optical prowess, but using one lens element less, while (most importantly) being far less expensive to manufacture.

Today, that early 8 element Super Takumar has a near-mythical status among legacy lens aficionados. However, the subsequent 7 element lenses are by no means bad lenses (and some even consider them better). Importantly, the 7-element design was the one Asahi/Pentax decided was the way to go, and even the current 50 mm f/1.4 Pentax-FA uses fundamentally the same design. It is therefore fair to say that the fast fifty has been even more central to Pentax as a company than it has to other camera companies.


The list below summarises the major steps in the genealogy of the Asahi/Pentax 50 mm f/1.4 lenses.

m42 mount lenses:
• 1964–1965, ‘Super Takumar’ 8 elements in 6 groups, IR index to the right of f/4
• 1965–1971, ‘Super-Takumar’ 7 elements in 6 groups, Product code 37800/37801/37802 (on aperture automation switch)
• 1971–1972, ‘Super-Multi-Coated’, 7 elements in 6 groups, Product code 37902
• 1972–1975 ‘SMC Takumar’, 7 elements in 6 groups, Product code 37908 [data sheet]

Pentax K mount lenses:
• 1975–1977 ‘SMC Pentax’, 7 elements in 6 groups, Product code 20847 (K-type Pentax K mount)
• 1977–1984 ‘SMC Pentax-M’, 7 elements in 6 groups, Product code 20867 (K-type Pentax K mount) [this lens]
• 1984–1989 ‘SMC Pentax-A’, 7 elements in 6 groups, Product code 20887 (KA-type Pentax K mount)
• 1987–1991 ‘SMC Pentax-F’, 7 elements in 6 groups, Product code 20827 (KAF-type Pentax K mount)
• 1991–2023 ‘SMC Pentax-FA’, 7 elements in 6 groups, Product code 20817 (KAF-type Pentax K mount)
• 2023– ‘HD Pentax-FA’, 7 elements in 6 groups, (KAF-type Pentax K mount)
• 2023– ‘SMC Pentax-FA Classic’, 7 elements in 6 groups, (KAF-type Pentax K mount)


If you want to natively mount this lens you need to find a functioning Pentax K mount SLR (or a dSLR) camera. Luckily that should be relatively easy as Pentax K film bodies were produced in their millions and most of them – especially those manufactured by Pentax – have a good reliability record. Alternatively, you can use this lens natively on any Pentax dSLR.

Adapting this lens to a mirrorless, full-frame digital camera is a breeze thanks to the lens having full manual controls (aperture ring, focus ring). You simply need a dumb adapter from Pentax K to your mirrorless system.

Due to the medium flange focal distance used by the m42 mount (45,46 mm), whether you can adapt this lens to other than Pentax’ dSLR mounts depends on which dSLR mount: Canon EF, and Four Thirds can mount Pentax K lenses using a simple adapter ring. Minolta/Sony A and Nikon F on the other hand are not as problem-free, and – to retain anything near infinity focus – the adapter will necessitate corrective optics. In all cases, your camera will work only in stop-down metering.


1 Focal length is (unless stated otherwise) given in absolute terms, and not in Full-frame equivalent. For an understanding of whether the lens is wide/tele, see ‘Angle-of-view’.

2 Picture angle is given in degrees (based on manufacturers’ specs) and concerns the diagonal picture angle. Rule of thumb:
> 90 ° ==> Ultra-wide-angle
70–90 ° ==> Wide-angle
50–70 ° ==> Moderate wide-angle
40–50 ° ==> ‘Standard’ or ‘normal’ lens
20–40 ° ==> Short tele lens
10-20 ° ==> Tele lens
5-10 ° ==> Long tele lens
< 5 ° ==> Ultra-tele lens

3 Length is given from the mount flange to the front of lens at infinity.

4 Diameter excludes protrusions such as rabbit ears or stop-down levers.

5 S=straight; R=rounded; C=(almost)circular at all apertures.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.