Pentax Lens Review: SMC FA 31mm f/1.8 Limited

Pentax K1 and FA 31mm

As a ‘Pentaxian’, being the quiet underdog amongst photographers is what I have got used to. When Canon, Nikon, Sony and Fujifilm users pull out their latest and greatest gear, all I can do is to keep accumulating shutter counts with my Pentax K-1. (By the way, even the K-1 was what I have waited almost 6 years for.) Pentax is definitely not famous for their lens release frequency or sales records, but there is a reason Pentax lenses up to 50 years old are still traded frequently in second-hand markets today: Pentax is special. The lens I am reviewing today is Pentax SMC FA 31mm f/1.8 Limited. For those of you who took an interest in photography not long ago, this is a lens you may not have heard of but may well be your favourite after reading this review.

SMC Pentax-FA 31mm F1.8 AL Limited

Why review a 31mm lens on

I have no intention to cover more than photography equipment and technique specifically with a 35mm lens. However, reviewing the Pentax SMC FA 31mm /f1.8 Limited (I’ll call it FA31mm for short) is an exception I am more than glad to make. The reason is simple: The Pentax FA 31mm, together with the 43mm and the 77mm, are arguably the best compact full frame lenses for photography enthusiasts. In 1997 Mr Hirakawa Jun, a Pentax engineer created the FA 43mm and FA 77mm lenses following the groundbreaking invention of a ‘ghostless’ lens coating originally rumoured to have been developed for an automated traffic identification system. It was ordered by the Japanese police to address the issue that flares caused by the car headlights made it impossible for the police traffic cameras to clearly record number plates. This coating is developed specifically for its superior ability to reduce flare.
The Pentax SMC FA 31mm F/1.8 is a miracle amongst Pentax lenses. when released in 2001 it was immediately recognised as the best wide angle lens Pentax has ever made. Photos taken by FA 31mm are said to have this mysteriously pleasing character that can only be seen but not shown in MTF tests. The combination of 7 group 9 elements design and the 9 blades aperture ring provide smooth bokeh. The 3D effect almost pops the subject out of the photo. Popular Photography wrote in its March 2002 issue that the Pentax 31mm Limited was one of the greatest prime lenses they had ever tested. 17 years later, in 2018 when I am writing this article, the legendary FA31mm is still in production and is loved by Pentaxians globally with the latest Pentax K-1 ii full frame camera.

Pentax 'the 3 Amigos'
the Three Amigos: Pentax FA Limited Prime lenses (31mm – left, 43mm,-right 77mm-middle)

Secrets of ‘the Three Amigos’

The common wisdom among Pentax users is that the unique focal length of the ‘three amigos’, the 31mm, 43mm and 77mm were compromises Pentax made in order to achieve the best physical attributes and optical performances. Even this 2017 in-depth review from said:

The design philosophy that went into the creation of the FA 31mm and its siblings is different from the usual wisdom applied when creating lenses. Instead of working with given focal lengths, specific apertures, and stringent requirements regarding resolution, the designer was given more leeway with the lenses’ specifications. This results in odd focal lengths (31 instead of 30, 43 instead of 50, 77 instead of 85) and unusual maximum apertures. Thanks to this shift in paradigm, FA Limited lenses are able to reach an astounding level of aberration correction (at the time of launch, at least), and offer unique rendering.

This, however, is not entirely correct. The focal length choice was not a compromise for the sake of aberration correction of rendering abilities of the lenses. The ‘three amigos’ are not a result of engineering innovation at the cost of optical lens industry design standards. They (metaphorically) dropped out of the modern ‘metric system’ school intentionally to worship the masters of yesterday: the imperial systems.

Let me reveal the secret for you: all three lenses are standard prime cine lenses: lenses specifically designed for the demands of cinema production.

43mm: is the diagonal length of a full frame film, equivalent to 1⅔ inch. This is a “true” standard prime lens for 135mm full frame films. This focal length is used by lenses pre-dates 35mm film cameras, mainly used by cine lenses on movie cameras. Some early Leica lenses are 1⅔ inch movie camera lenses.

31mm: 1⅕ inch is the diagonal length of a movie film (28 x 14). Therefore you can say a 31mm lens is a ‘standard prime lens’ for movie cameras.

77mm: equivalent to 3 inch, this is the diagonal length of 6×6 120mm medium format film. Therefore this is a standard prime lens for 120mm medium format cameras.

Mr Hirakawa Jun may have hidden a subtle Japanese style “Easter egg” that was meant to be a secret murmured and revealed only to those who went through the trouble of researching the history of filmography and photography. After the launch of the 43mm and the 77cm, Hirakawa’s initial design of the FA 31mm was not approved. Sadly Hirakawa was later made redundant after Hoya’s take over of Pentax. According to a Pentax forum rumour, he later went on to work from Tamron and will be retiring from Tamron in 2019.

Jorah Mormont - Game of Thrones
Jorah Mormont – Game of Thrones

The Knight of the Fallen Empire

Jorah Mormont in Game of Thrones is the exiled Northern lord from Westeros, a knight of the fallen empire. Lost the king he was loyal to, he wanders around the seven kingdom until became a spy. Later after growing respect and affection, he sworn fealty to fellow exiled Daenerys Targaryen.

Jorah’s story is just like the fate of the Pentax FA 31mm. After Hirakawa’s initial design, a 31mm f/2.4 lens was rejected by management for being too slow, and so the f/1.8 version came to be developed by another two designers, Takayuki Ito and Masayuki Murata. When it was released in 2001, Pentax was a huge camera manufacturer with 6000 domestic Japanese employees. 5 years later, it was taken over by Hoya in 2007 followed by a major restructure, leaving a tiny 400 domestic workforce in the Pentax camera department. The lens production has been shifted to South-Eastern Asia, mainly Vietnam. This includes the product of the Pentax SMC FA 31mm f/1.8 Limited. Despite all these changes of ownership, nothing has stopped the global interest in this lens until today. FA 31mm is used and praised with K-1 and K-1ii full frame digital bodies.

Why is the FA 31mm f/1.8 so darn good?

It starts from the very beginning. The lens was designed with the philosophy that technical measurement is a concern second to its actual photo rendering abilities.  The barrel distortion of the lens creates a ‘popping’ effect of the subject in the center of the frame. The sharpness at wide open is far from great in today’s standards, especially poor around the edges, yet the design is said to replicate the way human eyes see the world. At f/2.8 sharpness improves greatly, at f/4 the sharpness is excellent (some say it even beats the Leica R 50mm f/1.4 standard prime lens). The FA 31mm lenses were initially built in Japan before the production moved to Vietnam. If the serial number on the lens is before 16000, it was made in Japan with lead glass which is not as sharp and contrasty when wide open. When buying second hand, do check out for the ones made in Vietnam which do not contain lead-glass lenses with overall improved optical characteristics.

FA31mm is a compact, full metal lens with premium velvet lined lens cap and integrated, retractable lens hood. To make the lens as compact as possible, it uses a screwdriver autofocus system rather than a built-in electric motor. It does not have image stabilization for the reason that all modern Pentax DSLR camera bodies have them already. Being fully constructed with alloy, it has a beautifully grooved aperture ring and focusing ring which allow full manual control in precision. Without the use of plastic and rubber components, the lens construction is not weather sealed. It is only made to fit the Pentax PK mount but can potentially be used on other camera bodies with the right adaptor. People complain that the screwdriver autofocus system is a technology of yesterday. It is slow and not very accurate.

FA31mm is a full frame lens. Ironically during the majority of its production life, there was no full-frame digital SLR available from Pentax. FA31mm performed exceptionally well on the APS-C sized cameras, more or less as a 50mm equivalent standard prime. The softness at edges of frames is not an issue on the smaller APS-C sensor size due to the cropping factor, making the overall photo clarity and sharpness of FA 31mm on APS-C even better. Following the release of the Pentax K-1 and more recently K-1ii, the lens is becoming a prized item again with a steady increase in resale value.

Who is this lens for?

FA31mm is not for anyone using photography to complete an assignment or running a business. It is compact and sexy, almost too beautiful for the big, black, all mighty K-1. However its aut0- focus is mediocre: slow, noisy and sometimes cannot focus correctly with that screwdriver technology of the 90s.

The FA31mm is great for the more casual travel photographers who do not wish to carry heavy loads of gear when on the trip. To complement the Pentax K-1, you are able to bring along the ‘three amigos’ the 31mm, 43mm and 77mm (sometimes not even the 43mm) which when added together, weight less than a modern f/2.8 Canikon standard zoom lens. I usually mount the FA31mm on my camera and have a FA77mm in a lens pouch clipped onto my belt. This meets 95% of my photography requirements.

More generally, the FA31mm is for those who enjoy the photography experience as much as the end results. Just by turning the precision-machined focusing ring you will be able to not only see, but feel the quality of the top-notch craftsmanship of this lens. Like musical instruments, it is a lens with attached sentimental value beyond utilitarian value. It is one of those things that once you own and carry it, gradually it becomes part of you.

Buying New or Second-hand?

As mentioned earlier, there is a constant second-hand market for the Pentax SMC FA 31mm f/1.8. If you understand and accept the risks of buying second hand, have a look around your local camera shop and online forums. is a good starting point especially for those living in the US.

As of 2018, it is still possible to buy this lend brand new. For those who wish to collect it before Pentax eventually decides to cease producing this lens, it is not a bad idea to buy it new. We all know that Pentax as a brand is not doing extremely well now in this competitive market. From a commercial perspective,  I will be unwilling to see this yet will not be surprised if its parent company, Ricoh, makes a decision to end its production.

Did you know Pentax make other great 35mm lenses? Check out the 35mm Lens and Camera Database.

Books about the history of cameras and  lenses:

Check out my other articles on 35mm photography gear here.

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