Pentax SMCP-DA 21MM F3.2 AL Wide Angle Lens

In a recent review of the Pentax DA70 Limited lens, I discussed the time in history when lenses were hand assembled with precision metal components. I recalled my father's Olympus OM2n SLR with its metal lenses, smooth-operating focus rings, and compact feel of quality. Nowadays, we have grown accustomed to plastic lens barrels, polycarbonate components, nylon assemblies, and even rubber. We've almost forgotten what true quality feels like.

Pentax knows that there is a growing number of purists and enthusiasts out there; people who appreciate the way things used to be made. Photography is supposed to be fun, after all, and our tools should be inspiring. To that end, a few recent years ago Pentax began manufacturing and selling "Limited" lenses. The Limited designation in a Pentax lens denotes a lens made with real honest to goodness metal, and with top notch optical quality. They feature a metal barrel, metal components, superb optics, innovative ergonomics and designs, and by-hand construction to precise tolerances. They made no attempt at filling the spectrum with dozens of focal lengths. They picked three key focal lengths, and designed the best lenses they could in the three categories chosen. First they introduced a set of FA (optimized for film SLR's) Limited lenses; one wide, one standard, and one telephoto. And more recently, they've begun producing a set of DA Limited (optimized for Digital SLR's) lenses. The DA Limiteds have the additional distinction of being "pancake" lenses. Without their ingeniously designed hoods, each DA Limited lens is less than an inch thick when mounted on a body.

The SMC Pentax-DA 21mm f/3.2 AL Limited is a digital-optimized "Limited" for Pentax DSLR's designed to fill the need for a general purpose wide angle lens. The look and feel of this lens are excellent. Its metal construction, smoothly operating focus ring, and precision tolerances speak for themselves; this is a lens designed to be a pleasure to own and use... not unlike the well-made lenses of years gone by, but with new innovations only made possible by modern technology.

While we're on the topic of look, feel, and ergonomics, I should mention the hood. This lens features a click-twist-on metal hood of fairly unique design. It only extends less than a quarter inch from the front of the lens's body. Rather than extending forward, it instead resembles a lens cap with a rectangular hole cut in the front of it. This design enables it to provide a degree of protection and shading without adding considerable size to the lens. You might be wondering how a filter could work with this arrangement. The lens may either be used with no hood and a 49mm filter, or you may thread a 43mm filter into the inside of the hood. It's an interesting approach, and seems to work out fine. I'm reluctant to start accumulating a collection of 43mm filters though. Fortunately my standard 49mm ones will work too.

There are three caveats regarding the DA21 and its stylish hood: First, the stock push-on lens cap will only fit onto the lens with the hood attached, or with a 49mm filter attached. Without either hood or a filter, there's just not enough flange for the cap to grip. Second, the hood can accidentally be twisted off (unlatched from its bayonet) by twisting the lens cap the wrong way as you remove it. This can result in someone unfamiliar with the lens's operation actually disengaging the hood and losing it. ...and third: as of December 2007, Pentax USA doesn't stock the hood by itself. That means neither consumers, dealers, nor repair facilities (including Pentax USA's headquarters in Colorado) are able to obtain a replacement hood if you should happen to lose yours. Pentax Japan does stock the hood, so if you speak Japanese and have a means of arranging payment, you can order a replacement hood through Pentax Japan. Pentax USA's customer service department expressed to me that eventually the part will probably be offered, but at this time it's just "not in their system." Just be careful not to lose your hood, that's all. Now back to the lens...

The 21mm focal length, when mounted on a digital SLR, has the same field of view of a 32mm lens mounted on a film SLR. This is a very useful focal length for wide-angle photography. It presents one of those fields of view that a photographer can begin using and simply forget about for the rest of the day. My old FA28 was in a similar category, though the DA21 is obviously wider, and consequently more useful in landscape, street, or close-quarters photography. Ultra-wide angle lenses, in my opinion, are very difficult to use effectively. Composing a shot with a 14mm lens, for example, takes a lot more thought and patience than with a 70mm lens. I find that the DA21's field of view is right at that boundary; any wider would become difficult to use, and any narrower would reduce its usefulness as a wide angle lens. To me it feels like its focal length is in the proverbial sweet spot; still fun and easy to use, and still wide enough.

Optically the lens is very good. Wide open there is some vignetting, which evens out fairly well by f/4.5. Of course this light fall-off in the corners is easily correctable in post processing, and in fact is to be expected of a wide angle lens. At any rate, at worst its right around one stop of fall off, and stopped down one stop or so, it drops down to the point that it's not noticeable.

Chromatic aberration -- the divergence of colors as light hits the glass (think of what a prism does to light) -- is very well controlled with this lens. Only on a few instances did I feel compelled to correct for it. Most of the time it's really a non-issue with this lens. Pentax's digital-optimized lens coatings control it well, and also seem to keep purple-fringing at bay.

Sharpness is best in the center field, and falls off a little in the corners at open apertures. Overall it's quite good for a wide angle lens. I usually find that my own less than perfect ability to judge focus and my ability to hold the camera steady contribute more to degrading sharpness than the optics of this fine lens.

Rectilinear distortion is slightly stronger than I would have anticipated for a lens in this class, but the barrel distortion is by no means excessive. It would probably never show up except in the edges of a shot of a building or something similar. But it is there and should be mentioned. Fortunately simple barrel distortion can also be easily corrected in post-processing. ...fortunately for someone, I suppose. In my case I haven't yet felt the need to mess with it.

When I consider a lens for review, I try to think of one or two things that might bother people about the lens. I mean if I just wrote only the good, the review wouldn't be that helpful, now would it? Here is a list of what I might consider drawbacks. First, the hood has to come off if you're going to use ubiquitous 49mm filters. This issue is mitigated by the fact that a 43mm filter may be used with the hood in place. Second, the light falloff in corners, as well as reduced corner sharpness at open apertures. Both of these issues take care of themselves as you stop down a little, and at least with regards to the light fall-off, even if you do shoot at open apertures just about any modern post-processing software can quickly and effectively correct for it.

Another issue for some might be that its maximum aperture is f/3.2. Having shot a couple hundred frames with it already, I have to say that in the trade-off between size and maximum aperture, Pentax got it just about right. I wouldn't want to see it become 25% larger just to achieve 1/3rd stop faster. In fact, the other night I took it out shooting at night on Hollywood Blvd. It performed very well, and I never felt the need for a faster maximum aperture. The difference between f/3.2 and f/2.8 is apparently a non-issue.

Back to the positives: This is one of the first lenses for which Pentax has coated its front and back optics with a special coating that repels dust and fingerprints. It's easy to keep clean, and very durable. That comes in handy as the lens gets put through the paces out in the field. Despite its aesthetic beauty, this lens is made to be used.

Another feature now found in Pentax's DA lenses, but not in its older FA lenses is "focus shift." Once your AF camera body locks in an autofocus, you can still turn the lens's focus ring to "touch up" the focus. This is a surprisingly handy feature.

In conclusion, this lens is a pleasure to mount on the camera and just use. It's small, lightweight, and has a feel of quality that is rare nowadays. Image quality is very good; seemingly well above average, even when compared the standards set by nice prime (non-zoom) lenses. Together with the DA40 and DA70 (or their FA cousins), this lens rounds out the Limited kit, providing a perfect wide-angle focal length in a reasonably fast lens.