After a full twenty years on the market, Pentax is refreshing one of its most beloved lenses, the FA 31mm F1.8 Limited. Its unusual focal length, wide-angle view, bright optics, and aluminum construction have made the older SMC 31mm an all-time classic. The new HD edition features up-to-date coating for better durability and flare resistance, and rounded aperture blades to smooth out background blur. At $1,049.95, the HD FA 31mm Limited is a splurge, but it’s a lens you’ll be able to use for years to come, and one of our favorites for the Pentax system, earning it Editors’ Choice award.
Not Your Typical Wide Angle
The HD FA 31mm Limited comes in at an oddball focal length, in between more common 28mm and 35mm views. It splits the difference between the two, but has always felt closer to a true wide angle than the more in-between angle you get from a 35mm prime, at least on full-frame cameras like the K-1 and K-1 Mark II.
The view is more standard angle with Pentax’s APS-C line, which includes the most recent Pentax K-3 Mark III. The tighter view is good for singular subjects, and the wide aperture makes it an ideal choice for photographers with an eye toward subject isolation in photos.
Mechanically, the HD edition of the lens is the same as the original SMC FA 31mm introduced in 2001. It measures 2.7 by 2.6 inches (HD), weighs about 12 ounces, and supports 58mm threaded filters. The lens is exquisitely constructed, with an aluminum barrel, integrated petal-style lens hood, and felt-lined metal lens cap. A leatherette drawstring pouch is included too. Pentax sells the 31mm Limited in a black or silver finish; we received the former for review.
Like many other Pentax lenses from its era, the FA 31mm Limited includes on-lens aperture control. You’ll leave the ring set to its A position when using a digital Pentax or a 35mm SLR with electronic aperture control; it can be set manually from f/1.8 through f/22 for use with older film cameras, as well as with simple mechanical adapters for mirrorless cameras.
Broad compatibility is welcome. The aperture ring means you can use the lens on vintage film cameras dating back to 1975. This includes the K1000, still a favorite in used camera shops, and the 1980s-era LX. I used the latter to run through a bit of film with the HD 31mm and its updated siblings, the HD 43mm and HD 77mm.
There is a feeling that, in looking backward, Pentax is limiting what it can do with the FA 31mm. Whereas Pentax has put weather sealing into its SLR line as a baseline feature since the K10D era, the 31mm isn’t protected from the elements; it’d likely take a redesign to incorporate the feature. The new-for-2021 FA Limited 21mm F2.4 DC WR, the only all-weather lens in the series, skips the aperture control ring.
I paired the FA 31mm with a few different cameras for review, including the K-1 Mark II and K-3 Mark III. I also tried the lens with the Sony a7R IV using the MonsterAdapter LA-KE1, the first cross-system adapter with autofocus and electronic aperture control for Pentax lenses. Autofocus with the adapter was a smidge slower than with the K-1 Mark II, but other than that results were good.
Handling and Autofocus
The FA 31mm is the largest of the original Limited trio, but is relatively undersized compared with many modern prime lenses, including the chunkier Sigma 35mm F1.4 Art (3.7 by 3.0 inches, 1.5 pounds), one of the few third-party lenses available for the Pentax system. At around 12 ounces, the FA 31mm balances well on the K-1 Mark II and K-3 Mark III alike.
Autofocus is driven by your camera’s screw-drive system. It makes for quick acquisition—the K-1 Mark II drives across the full range in a half-second, and the K-3 Mark III is a little quicker. It’s noisy, though; you can hear the autofocus whir across a quiet room.
There’s also some movement during autofocus. The front of the lens extends a little, less than a quarter-inch, and the manual focus ring moves along with it. The ring is metal, with a textured ridge finish, so you’ll want to keep your fingers clear when using autofocus.
It’s a joy to use for manual focus. The focus ring turns with enough resistance for fine control, but a light enough action to twist with just your index finger. A cutout window shows the set focus distance in feet and meters, complete with a corresponding depth of field scale.
Focus is available as close as 11.8 inches, good enough for 1:6.3 life-size magnification at its nearest distance. It falls short of macro—if you’re in search of close-up focus, the HD DA 35mm F2.8 Macro Limited is made for APS-C cameras, but does a pretty good job on full-frame and focuses close enough for 1:1 capture.
The mechanical focus system offers a linear response, good for videographers who want to repeat the same shift in focus from take to take. Focus breathing, a distracting effect where the angle of view shifts along with focus, is visible though, so the FA 31mm is less than ideal for rack focus shots.
The HD coating is a step up from the older SMC version for shots into the sun or against a similarly strong backlight. Pentax Super Protect (SP) is another addition. The fluorine material repels grease and moisture, and adds some scratch resistance to boot. With some care, the FA 31mm Limited should stay in service for decades.
Pentax manufactures the HD FA 31mm in Vietnam. The first decade or so of SMC FA 31mm Limited production was in Japan, and while some are willing to pay a premium for Japanese copies, there’s no discernible difference in quality between the two made-in-Japan copies of the SMC FA 31mm Limited I’ve owned over the years and the made-in-Vietnam HD FA 31mm.
HD FA 31mm F1.8 Limited: In the Lab
The HD FA 31mm is sharp in lab tests. I paired it with 36MP K-1 Mark II and software from Imatest to check its performance. As expected, it delivers right in line with the SMC version of the lens, with good results wide open (2,300 lines) and excellent marks stopped down (3,000 lines).
The field of focus isn’t quite flat, so the lens doesn’t score well at the periphery when photographing test charts and other flat objects. In the real world the curvature gives wide aperture photos a bit more pop against a blurred background, especially when working closer to your subject.
Distortion is well controlled, too; there’s only a hint of the barrel effect in photos. If you use your camera in JPG mode a correction is applied automatically, and Lightroom includes a one-click profile for distortion in Raw files. The profile also compensates for an optical vignette, visible at apertures wider than f/2.8.
The optical design is two decades old, and it shows more chromatic aberration than we’re used to seeing in modern lenses. The lateral type, purple color fringing, is fairly modest, and easily wiped away using software tools when it does pop up. The K-1 Mark II suppresses it for JPGs and Raw processors rub it out easily.
Longitudinal chromatic aberration (LoCa) is what’s troublesome—it shows up as false green and purple halos in the areas of transition between focus and blur. It’s not visible in every image (far from it), but if you’re sensitive to LoCa, this may not be your lens. On the other hand, you might be looking at the FA 31mm because of its character, and technical flaws are part of it.
Another part of the FA 31mm’s character is defined by the way it draws backgrounds. Rounded aperture blades make a very slight difference versus the older SMC 31mm—instead of octagonal highlights at f/2.8 and f/4, you get circles. There’s less difference at f/1.8 and f/2—both versions of the lens draw circular highlights, with only a slight cat’s eye shape at the edges of the frame.
The bokeh can be a little busy, too. The lens tends to draw very small circles in the background, a bubbly look, and if you catch the right light the LoCa effect gives highlights a slightly hard edge. It’s not as extreme as a soap bubble specialist like the Meyer Optik Trioplan 100 F2.8 II, though.
Rounded apertures can be bad news for sunstars, but that’s not the case here. The SMC 31mm doesn’t show defined sunstars until stopped down to f/8 or smaller. The HD 31mm’s sunstar effect also kicks in at f/8, and shows more clearly defined points down through f/22.
An Heirloom Lens
When older photographers lament that newer photo gear isn’t made as well as the old stuff, the FA 31mm is the type of old stuff they’re thinking of. I suppose I should count myself among them, as I’ve got some personal history with the SMC FA 31mm F1.8 Limited. My first DSLR was the 6MP Pentax *ist DL, and I went with the 31mm when it was time to upgrade from the 18-55mm starter lens.
Even in the 6MP days, the jump in clarity and depth was apparent. It’s the lens I used most when I was learning how to use a camera, and remains one of my favorites to this day. At one point I sold my first copy, in silver, only to buy another (in black) a few years later. It still gets use, though not as much as I’d like.
Picking up the HD FA 31mm F1.8 Limited for review felt like reconnecting with an old friend. The updates are modest, but make the HD edition a more practical choice. The new version of the lens better suppresses flare, is easier to clean (and keep clean) thanks to its SP coating, and has all the character of the original.
You pay for it, though. Prices for the SMC FA 31mm have fluctuated over time, but it’s always been a spendy lens. At $1,049.95, the HD edition comes in $50 lower than the SMC’s most recent retail price. Pentax photographers have a couple lower cost options to consider—the Sigma 35mm F1.4 DG HSM Art for $900 and the Pentax HD 35mm F2 for $400—but neither ticks the same boxes as the Limited.
While we would have welcomed a redesigned housing with weather protection, we can’t fault Pentax for keeping an old favorite in circulation. In an ever-changing photo market, the FA 31mm has endured for decades, and its deserved reputation has only improved. This is one of my all-time favorite lenses, a must-have for any Pentaxian, and an Editors’ Choice.
