Lens Reviews

This article has been many years in the writing. Of the three Pentax lenses Ethan owns, the 31mm is the one we have never commented or written about. Ironically, it is the one lens that sees regular use when out shooting with Pentax DSLR’s. It is also the most favoured of the three and has been quietly doing its job for more than a decade. We were recently carrying out an evaluation of the PhotoArk site and from this it became glaringly apparent that writing anything about it had slipped our attention. The reason for this is that when we onboard a new piece of kit, we do not ‘rush and gush’ our thoughts, preferring to let time and experience temper enthusiasm. By doing this we believe that it provides a more balanced opinion which can only be garnered long after the honeymoon period ends. And so it was that our favourite Pentax lens was completely overlooked. This article redresses this and after such a long time in use it gives this beautiful piece of engineering its moment in the sun from a PhotoArk perspective.

pentax fa 31mm lens 1When it comes to technical specifications, we are years too late producing anything that could be considered unique - the opportunity for that fled over the hill a long time ago. But what is interesting is that the lens remains in production more than 25 years after its introduction. In that time we have seen a couple of revisions that introduced HD coatings that purport to help with digital sensors, along with redesigned circular aperture blades. Whether these changes made any significant improvements in the optical quality, we do not know as we have never compared the different versions side by side. Aesthetically, little has changed externally resulting in the gradual evolution of a product that remains true to its design ethos of traditional lens manufacture. In these days of large austere looking prime lenses, the entire limited lens series looks like a throwback to an earlier time, in much the same way as modern Leica M lenses do.

The 31mm is one of a trinity (known to Pentaxians as the ‘Three Amigo’s’) of highly prized ‘Limited Series’ of lenses, the others being a 43mm f1.9 and 77mm f1.8. In the context of these lenses, the word ‘Limited’ does not relate to limited production runs or editions. It refers to a lower production volume where priorities are given over the materials used, assembly and quality control. Paying more attention to these aspects invariably reduces production capacity. As they can probably be considered niche products in today’s marketplace, it is unlikely that demand outstrips production.

What is immediately apparent when using the 31mm is its tiny size. Although it is the largest of the trinity, its dimensions are still pretty diminutive for an autofocus lens. We have only used it on the APSC format K3 mkII Prestige and, before that, a K5. As these bodies are also fairly small, it matches perfectly and does not appear unbalanced. The metal lens barrel and 9 elements in 7 groups optical construction give it a feel of robustness along with a jewel-like quality. It is one of those optics that I can simply pick up, study and admire without actually using it. The presence of an aperture ring gives the lens added appeal to those who appreciate a more old school approach. Click stops are well damped, not quite up to the feel of the ring on my Q2, but far better than nearly all of my older OM System film lenses - some of these were very rattly. 

Sadly, the lens is not fully environmentally sealed so care should be taken in harsh weather conditions or situations where there is a lot of airborne particulates. However, an all important rubber gasket surrounds the mount, going some way to protecting the camera internals. We have never experienced any problems using it in light rain or desert conditions in more than a decade of use. Adding extensive weather sealing would inevitability add to the overall dimensions, maybe compromising the limited series ethos. 

The autofocus design is archaic by modern standards and deploys a screw drive solution that is a tad noisy but very accurate. We have rarely had any issues with focus apart from occasional low contrast or hunting in poor light. It has never been bothersome and can easily be overrode with manual focussing (of which the presence of a grippy focus ring helps). In these days of silent autofocus motors and lightning fast focus speed, it could be argued that the 31mm feels dated. Using experience as a mitigating factor, we are confident in saying that it has never failed in all of the years we have used it and the speed, while not bleeding edge, has always been fast enough for our needs.

There has been some criticism regarding the 31mm’s performance wide open. This has been centred around the presence of Lateral and Longitudinal Chromatic Aberration in high contrast areas and an overall softness of the image. Some users found this unacceptable in a lens as expensive and highly prized as this, opting to sell their copies on. We do see this at f1.8, but CA is much less noticeable when stopping down to f4. Much of what is present can be removed in post processing with software such as Lightroom. The image sharpens up in the centre nicely by f2.8, becoming incredibly sharp across the entire Frame at f5.6. The softness at f1.8 can be exploited and should be considered part of the 31’s character. Using the lens wide open allows the photographer to lean into the soft nature in the same way as we did with our OM System Zuiko 50mm f1.2 from our film days. This was notoriously soft at f1.2 but at the same time, introduced a dreaminess to images that we found appealing. As with the Zuiko, simply stopping the lens down sharpened things up immensely. Having at least one lens with these qualities in a photographers arsenal expands creative horizons further than having all lenses aligned as close to optical perfection as possible. Also present at f1.8 is noticeable vignetting which again, can be exploited to taste. Unlike some other lenses we have owned, vignetting of the 31mm can be simply removed in post processing, but again this is gone when stopped down a little.

There is no doubt that the optical character of this, and other FA Limited lenses is a compromise between form factor and performance and will have been a design choice to allow this family of lenses to be built as small as possible. In the photographic world, perfection abhors miniaturisation and this was never more evident than with several of the old film Zuiko lenses we used. A lens that is just a couple of centimetres long, weighing in at less than 350 grams and containing minimal elements is never going to perform as well as a design that does not compromise on size and weight.

Ghosting and flare are very well controlled and have never caused us an issue at any aperture. The built-in lens hood included contributes excellently towards making these a non-issue.

pentax fa 31mm lens 2Overall, the results from the 31mm are incredible, and more so when you consider that it has been in production without any big changes since inception, more than two and a half decades ago.  The colour balance is neutral and realistic. Neither are the results too contrasty. As we only shoot RAW and enjoy post processing, this means the output is perfect for editing. On many occasions we leave the RAW colour profile well alone, preferring to let the lens’ capabilities shine. Black and white conversions work very well and remind me of conversions from some of our Leica lenses. I am not sure why this is…maybe the micro contrast and other optical nuances work in concert to reward the user. We would like to try it out with the K3 mkIII Monochrome, along with some of the other Limited lens series.

When it debuted, film was dominant and the 31’s performance became legendary. While we do not have a Pentax K1 to use the lens on, many users have stated that it complements the K1 mkI and mkII cameras beautifully. The APSC cameras we use it with introduce a 1.5 x conversion, making the focal length behave like a 46.5mm optic. Having it act as a standard lens was precisely the reason for its purchase all of those years ago. Embracing its relatively minor shortcomings ensure a life long companion, and one that barely takes up any space in a bag.

One thing that has surprised us both over its long production run is that it is still available in black or silver finishes. Given Pentax’s transition into the niche camera sector in recent years we thought that the silver finish would be discontinued. It is heartening to see that the people at Pentax remain committed to producing the Limited series of lenses in both colours. It shows true commitment and attention to detail that puts some mainstream brands to shame. A close family friend has the 31mm in the silver finish and it looks very classy.

Would we buy this lens again? Absolutely. Spending time writing this article has given me a renewed appreciation of the Limited range of lenses. In fact it has led to something of a renaissance in my own personal interest in the Pentax brand. At the time of writing, I am awaiting delivery of a K3 mkIII and 20-40 Limited lens, both in silver. Lens appeal aside, I am looking forward to using an optical viewfinder again although, being a Leica user for many years, not looking forward to using a camera bristling with buttons and menu options. A dalliance with Pentax is a means to an end for me; and that is to allow me to use some of the brands wonderful lenses more.