[Review] FA 31 mm f/1.8 Limited [2021]

FA 31
Lens test of Pentax FA 31 f/1.8 Limited was made with a Pentax K-1 mk II  -  Traduction : fyve & Micaz  -  French Version here

 

The FA 31 mm f/1.8 Limited began its career in 2001, shortly before the release of the MZ-60, one of the last Pentax films SLRs. When these disappeared, the 3 FA Limited lenses remained in the brand’s catalogue, despite Pentax only offered APS-C cameras. For many photographers , it was the hope of a full format DSLR (the « 24×36 » format). This hope was finally realised at the beginning of 2016. On this occasion, it regained all its original specificity, the one offered by this very special focal length that is the 31mm.

Nevertheless, although this lens was designed for Full Format, it can still be used on an APS-C body, even if the focal field is smaller (about 48 mm).

Overview of the Pentax lens FA 31 f/1.8 AL Limited SMC

This wide-angle lens belongs to the limited series. For some pentaxists, it is endowed with extraordinary powers in terms of photographic quality. The signature of the Limited ? An excellent optical quality and a colorimetric rendering that is supposed to be exceptional. The FA 31 is the most legendary of the FA Limited series (which also includes the FA 43 and the FA 77). That’s why we expect a lot from it.

The Limited label

The main ideas of the limited series were to :

  • make the photographer forget the lens, in order to focus on the photo itself (compactness and lightness),
  • propose a rendering and a finish of the images that would faithfully reflect the mood of the scene,
  • propose a larger aperture,
  • typical in the focal length,
  • retain the manual aperture setting,
  • stand the test of time thanks to their touch and elegance.

With the FA Limited series, PENTAX wanted to design lenses that were compact and easy to handle. The lens also needed to effectively control aberrations and optimize image depth and sharpness. Contradictory objectives when we see that modern wide-aperture lenses are increasingly heavy. Today, to optimize resolving power and contrast while minimizing various aberrations, engineers are add some complementary optical elements.

For this purpose, particular care is taken during the manufacturing process. FA 31 and 77 lenses are finished by hand. The barrels and all exterior components are machined from high quality aluminium material to optimize the visual design.

While the FA Limited (FA 31, FA 43, FA 77) fully respected these principles, the DA Limited (DA 15 , DA 21, DA 35 Macro, DA 40, DA 70 and DA 20-40) did not. The latter have indeed dispensed with the manual adjustment of the aperture When the DFA 21 is released, we will see if other hiccups will have been made to the original rules.

Do you know ?

A first version of the FA 31 was developed by Jun Hirakawa, the engineer who desisigned the FA 43 and FA 77. This FA 31 opened at 2.4 and was based on the optical formula of the K Prime 30 mm f/2.8 lens (produced from 1975 to 1984). This FA 31, although very compact, did not meet the expectations of the brand’s managers. They criticized it for being too slow to focus. The second and current version was designed by a new team (Ito Takayuki and Murata Masayuki).

An old-fashioned design

This is the first impression you get when looking at the FA 31. An all-metal lens. For those who are sensitive to the silver color, there is a classic black and a silver version. Both models, except the color, are strictly identical. To each his preference.

FA 31 limited, black et silver
FA 31 Limited, black & silver (© Ricoh Imaging)

 

What’s a 31 mm for ?

The FA 31 offers a very interesting focal length for photographers because it is versatile. It can be used for landscape, reportage, street photography, urbex, etc… And portrait if the subject is not too far away! Like a 35 mm, this focal length does not distort perspectives as much as a 24 mm and it does not tighten the different shots as a small telephoto lenses (77 to 120 mm) would do.

The 31 mm, by framing a little wider than a 35 mm, also allows more space in the image. This not only allows the integration of peripheral elements that may be of interest (set, scene, additional elements) and allow the reader to situate the subject in its context, but also to let the main subject of the image breathe.

Getting Started

An all-metal lens is becoming increasingly rare. This construction is one of the requirements of the « Limited » specifications. And, even if it makes the lens heavier than a polycarbonate construction, there is a typical nostalgic scent perfectly assumed. This perfume is also found in the presence of an aperture ring. Attention, unless you wish to manually change the aperture (in this case, you will have to set up the body), the ring must be set to « A » position (Automatic). I can’t count the number of times I couldn’t trigger because the ring had rotated without me realising it!

This ring is sometimes difficult to access on the K-1 due to the prominence of the pentaprism block. Pressing the push button to switch to « A » mode can be more complicated if you have big fingers. This is not an ergonomic problem related to the lens, but rather to the body.

FA 31, an old conception lens
An old conception lens (© Ricoh Imaging)

 

The last nostalgic detail is the presence of a very complete screen printing for the distance indicator (from 0.30 m to infinity). An « assistance » to the development that some people will appreciate when they think back to their younger years. An older, but more complete version of what can be found on some modern lenses. At least when it is present…

The dimensions of the lens are modest (69 x 65 mm) which makes it practical to use. The all-metal construction is less warm, in every sense of the word, than a polycarbonate/rubber construction. In winter, the lens will remind you of its coolness!

The tooth focusing ring is wide enough to allow good use even with a large hand and/or somewhat thick fingers. No discomfort, other than the one mentioned above, hinders its use. It rotates smoothly and flexibly. In terms of ergonomics, there is not much to be reproached. And its stylish design gives it a crazy class.

 

Handling : 7

 

Main technical data of the FA 31 Limited

Technical data (click to see)
PENTAXPentax FA 31mm f / 1.8 AL ED LimitedMonture KAF2
KAF2 Mount
Specifications
Focales
Focal lengths
31 mm
Equivalent 35mm sur un APS-C
35mm equivalent on an APS-C camera
48,8mm
48,8mm
Angle de champ / de vue
Angle of view
70° avec un boîtier numérique Pentax

70° with a Pentax DSLR
Plage d'ouvertures
Aperture Range
f/1,8-22
Diaphragme
Diaphragm
9 lamelles
9 blades
Lentilles - Groupes


Elements - Groups
9 lentilles en 7 groupes
1 lentille asphérique AL- 1 lentille en verre ED (Extra Low Dispersion) 1-lentille à dispersion anomale (Anomalous Dispersion)

9 elements in 7 groups
1 aspherical lens -1x element with Extra Low Dispersion (ED) glass -1 element with Anomalous Dispersion glass
Distance minimale de mise au point
Minimum focusing distance
0,30 m
Grossissement maximum
Magnification ratio
0,16X
QuickShiftNon - No
Moteur AF
AF Engine
Non - par le boitier
Screwdrive
Autres
Others
Diamètre de filtre
Filter diameter
58 mm
Tropicalisation
Weather protection
Non
No
Dimensions
(longueur x diamètre) (Length / diameter)
68.5mm x 65mm
Poids
Weight
345g
Accessoires

Accessories
Bouchons avant & arrière - Pare-soleil - Sac

Front and rear caps - Hood - Bag
Compatible FF
FF compatibility
oui - objectif FA

Yes - FA type lens
Optical formula

This optical formula consists 9 elements divided into 7 groups. Pentax did not use a historical Planar or Sonnar-type optical formula (French version only). The formula seems original. It is complex for a simple 31 mm lens.

Schéma optique du 31 mmf/1.8 Limited
Optical formula of the Pentax FA 31 mm f/1.8 Limited (© Ricoh Imaging)

 

 

The construction includes 2 ED (low-dispersion) glasses to reduce chromatic aberrations and increase sharpness and color rendering. They are both placed at the outer end (positions 1 and 3). An AL (aspherical) element is present at the other end (sensor side), in the penultimate position. A design with a dual purpose :

  • improve optical performance at the image periphery
  • reduce geometric distortions as much as possible.

As the design is old, the results obtained by this arrangement will have to be carefully examined.

The diaphragm consist of 9 blades. From f/1.8 to f/5.6, its shape remains relatively rounded. Beyond that, the shape is not really round anymore.

The mount is KAF2.

Nostalgia does not only have good sides

This objective dates back to 2001. It was designed with the criteria for use in the late 1990s. Since then, the standards have changed and some features have become essential for the public. For example, to be able to use the FA 31 when it rains, when going to the beach, to the snow or during a particular climatic event. These are photographic practices where the risk of dust or water getting into the lens and body is highly increased.

Tropicalization is one of the features expected by photographers. Especially for a lens that has such a wide range of possible uses. It is a shame that one have to limit its use out of fear.

Construction quality

As already mentioned the lens is an « all-metal » type, including bayonet, and the weight is moderate. These are great advantages.

By modern criteria, this Limited is technically outdated. It is not tropicalized as we have seen, but there are other issues that may trouble some photographers. For example, the absence of a silent DC, SDM or PLM type motor. But for a wide angle, is a motor important? Shooting comfort is improved, especially when the sound volume is low (the use of the motor inside the camera body is always noisier). Nevertheless, adding an engine has a disadvantage, that of being overweight. Size and weight are increased, as we will discover with the future DFA 21 Limited.

Last significant missing is the quickshift. A feature to be forgotten on this FA 31, the design being too old.

 

Construction & Finition : 7

Specification (technical) : 8

Main optical data

PENtaxKlub does not have a laboratory. Our tests are not measured by tools. We wish to bring a user and essentially photographic point of view. Our comments and technical note are therefore the result of a visual analysis.

Please note that for any lens, even the best one, it is always possible to obtain visual imperfections (especially with ACs), whatever the focal length and/or aperture.

Test pictures

All the photos used for the tests were taken in RAW format (PEF or DNG). Unless explicitly mentioned, not developed or not retouched.

Focusing areaFocal lens length 31 mm
FA 31, zone de mise au point
In pink, the focusing area

Framing without the right and left flaps was impossible.

ApertureEntire pictureDetail
f/1.8  (W.O.)f/1.8 image entièref/1.8 extrait au centre
f/2f/2 image entièref/2.8 extrait au centre
f/2.8f/2.8 image entièref/2.8 extrait au centre
f/4f/4 image entièref/4 extrait au centre
f/5.6f/5.6 image entièref/5.6 extrait au centre
f/8f/8 image entièref/8 extrait au centre
f/11f/11 image entièref/11 extrait au centre
f/16f/16 image entièref/16 extrait au centre

Any lens is likely to produce chromatic aberrations (CA) and flare.

CAs appear as a purple (or green) fringe, unpleasant to the eye. They form when the 3 colors of white light (Red, Green and Blue) pass through a lens, separate and do not meet in the right place to produce a sharp image.

Flare occurs in certain light conditions, such as when the sun sends its rays at an angle to the lens.

This is why we prefer to judge a lens in common and not exceptional image situations

Chromatic aberration

Chromatic aberrations (CAs) are (very) present. They are both green and violet. The association of the 2 colours is not frequent. Very present from WO up to f/2.8, they gradually disappear until f/4, at which point the CAs become almost non-existent.

But this phenomenon should be put into perspective for several reasons. The result is much better than it seems.

  • CAs are present in specific surfaces, but not everywhere.
  • They remain light and do not really disturb. Moreover, it’s easily corrected with modern post-processing tools.
  • With a 31 mm, taking pictures full aperture is not frequent. And when it happens, it is often in the presence of light conditions that do not lend themselves to the appearance of CAs.
  • This is the low price to pay for a compact and light lens!
Flare

If you place yourself in conditions that favour them such as strong backlighting or sun in the field at 45°, flare phenomena can appear at large aperture. Even the most expensive lenses can be affected ! They generally disappear after 1 or 2 f-stops down.

In common use, the flare resistance seems very good even if it can be provoked. When there is, by stopping down between f/2.4 and f/4, it disappears. This FA 31 mm seems to be quite resistant to this phenomenon. When the latter does occur, the aperture is often below f/2.8. Some modern lenses (like the DFA 24-70 / 2.8) are more sensitive than this FA 31 Limited.

Vignetting

When there is, by closing between f/2.4 and f/4, it disappears. If in the majority of cases, at f/2.8 the problem is solved, in certain very bright conditions, it will be necessary to wait for f/4. But again, this is not a true problem.  It even brings an interesting feature to the pictures. Like a signature. In addition, Post-Processing software tools will be able to correct it easily.

Distorsions

The optical formula works wonders because the barrel type distortion at f/1.8 is not disturbing. And most importantly, it is easily corrected using the Post-Processing tools. This distortion persists up to f/22.

FA 31 à 1.8, distorsions corrigéesFA 31 à 1.8, distorsions non corrigées

Unfortunately, even if this distortion is minor, it does exist and causes points to be lost for the lens rating.

For those who take pictures in JPEG, remember to activate the automatic lens correction proposed by your Pentax camera.

Image Homogeneity

The homogeneity between the center-field and the border-field is already good. This is quite impressive for an « old » formula, not intended for digital cameras. Especially at a time when engineers are telling us that we need to add optical elements to meet the needs of digital sensors.

At f/1.8 (WO), sharpness is present around the focus point, but it’s not perfect. We notice the presence of fog. Closing at f/2, sharpness becomes as good in the centre-field as in the border-field. There is still an impression of blur over the whole of the shot, but it is very weak (remember that at f/2, the focus area is narrow).

f/1.8  (WO)  CenterCentre champ à f/1.8Centre champ à f/1.8 extrait
f/1.8  (WO)  BorderBord champ à f/1.8Bord champ à f/1.8 extrait
f/2   CenterCentre champ à f/2Centre champ à f/2 extrait
f/2  BorderBord champ à f/2Bord champ à f/2 extrait

Since good sharpness is obtained from f/2 (barely 1/3 of IL after the WO), we will not consider this point as discriminatory for the final score.

Bokeh

It’s a 31mm and therefore a Wide Angle. Bokeh is not excellent when you’re far enough from the target. When the main subject is near the photographer bt far from the bottom, you can have some good sensations. We still manage to take test photos. Up to f / 2.8, the bokeh is very nice. After 2.8, we start to see the background better. At f / 8, if the background is far enough away, it is present, but still a bit blurry.

Focusing area - Aperture f/2.8focal length 31 mm

FA 31 à f/2.8 - Bokeh zone de map

f/1.8 (WO) – Subject to approx. 1.2 mf/4 – Subject to approx. 1.2 m
Bokeh à f/1.8Bokeh à f/4
f/8 – Subject to approx. 1.2 m
Bokeh à f/8

 

Image quality (homogeneity, sharpness, distorsion) : 31

Optical quality (Aberration, flare, vignetting) : 21

With an APS-C body

The conversion factor of 1,52≈ which affects the focal field (it « becomes » a 53 mm ≈) has the same behaviour on the aperture. The « real » aperture will therefore be closer to f/2.4. This will directly influence the production of AC (there will be less of it), the flare, the sharpness and obviously the bokeh (we are closer to a 50 mm f/2.8 in the rendering). The interest is therefore less.

Price and Competition

A point on competition. The tests follow one another and the comments are more and more identical on this subject. There is almost no competition from independent opticians. Tamron has not produced for Pentax for a long time and Sigma has decided to do the same with the few remaining K bayonet products. If you find new Sigma, it will necessarily be from the end of the series in destocking.

The competition is therefore internal. In the absence of a fixed focal length at 28 mm, we will turn to the FA 35/2 HD (with aa nearly aperture) which is experiencing a new lease of life with the HD version (and its falling price). There also remains the zoom solution with the DFA 15-30/2.8 (at 30, we are only at 1 mm) and DFA 24-70/2.8. But in all cases, the rendering will be different.

The price remains. At 1499 € (in France), it seems monstrous, especially when the FA 35/2 HD is at 399 €. For second hand, it’s worth between 750 and 850 €.

 

Conclusion

Not very convinced when using it with an APS-C, I fell in love with this lens when I got my K-1. So it joined my collection.

Its focal length is more atypical than the 35 mm, because it offers, thanks to its 4 mm less, something more. But it is more about the rendering of the images that it is superior than the other lens. The Limited brings an extra magic. Not that of silver, no, but something else, quite indefinable. Once you’ve appropriated it, you can come up with fabulous shots. This is an excellent lens, whose note does not really reflect its deep quality. This paradox is due to the rating, which places great importance on sharpness and resistance to CA, reflecting what the public of the 2020s expects from a lens.

The only thing one could regret is that an optimised version does not come out. A tropicalized HD version, all for 1000 €.

 

PROsCONs
  • The atypical focal length
  • Colour rendering
  • Homogeneity of the image
  • Sharpness from f/2
  • Sometimes a little too much CAs (but that can be corrected very easily)
  • Price

 

Logo EN Recommanded

Note

Handling7Light and well-balanced, it is forgotten once installed.
Construction & Finition7An excellent construction that will only really suffer from the absence of tropicalisation.
Specification (technical)8Lack of tropicalisation and internal motorisation? But in the 1990s, these functionalities were almost non-existent…
Image quality (homogeneity, sharpness, distorsion)31An almost faultless course, which is remarkable.
Optical quality (Aberrations, flare, vignetting) 21It loses points because it produces CAs up to f/4. and vignetting under certain conditions.
Overall rating74/100

 

Gallery

The photos in the gallery may have been developed.

Esplanade de La Défense (ajout d'un vignettage en PT)
Esplanade de La Défense (vignetting adding in PT)
Palais du Luxembourg
Palais du Luxembourg… before Covid 19 !
Paris la nuit
Paris at night, when there was no curfew
Fontaine, place de la Concorde
When you could still take pictures at night!
Entre Aubagne, Marseille et Toulon
Just after midnight, between Aubagne, Marseille and Toulon
Métro confiné
The Saint-Lazare subway station, a day of confinement!
Face à la mer… ???
Facing the sea… no, facing the Seine!
Grande marée parisienne face au FA 31
The FA 31 to the test of a big Parisian tide
Là où Benjamin Franklin arriva
Where Benjamin Franklin arrived
Le FA 31 et les lumières d'hiver
The FA 31 and winter lights

 

Photo credits: © fyve – The pictures are the property of the author (unless specified) – Click to enlarge