HD Pentax DA 21 f3.2 Limited

The HD Pentax DA 21 f3.2 Limited is a moderate wide-angle “pancake” lens designed for APS-C DSLRs. Measuring only one inch in length and weighing just 4.9 ounces, this is a small, compact prime lens that can easily fit in a pocket and be taken anywhere. It’s in many a “throw-back” lens: all metal (aluminum) and glass build, with distance and DOF scales. Even the compact hood and felt-lined lens cap are made of metal.

There exist two versions of the lens: the first version makes use of Pentax’s “SMC” (which stands for Super Multi-Coated) coatings (possibly combined with Pentax’s “ghostless” coating technology introduced in the late nineties) and features irregular aperture blades; and the newest, second version, makes use of Pentax’s state-of-the-art “HD” (High Definition) coatings and features rounded aperture blades. I’ve written about the HD coatings in my review of the HD DA 16-85. Besides their technical excellence, they also appear to be relatively inexpensive to apply (unlike slightly more advanced “nano” coatings). Ricoh describes the process as follows:

Typically, multicoatings are formed by using vacuum deposition to apply a thin layer to the lens surface. However, this fabrication process also presents problems because of the difficulty in increasing the density of the coating film and the variation in refraction rates and film thicknesses. PENTAX's solution to these problems was our HD Coating, which is fabricated using PENTAX's exclusive special fabrication process, where high-density film is applied with high precision at the nanometer level. This enables the reliable formation of the designed film thickness for a dramatic reduction of the reflection rate (up to 50% compared to conventional coatings) over the entire visible light range. It is also effective in reducing ghosting and flare. Moreover, the film coating has an extremely high hardness for providing superior durability.

A graph demonstrates the difference between HD coatings and “conventional” coatings:

According to this graph, HD coatings show significant improvement between 450nm and 600nm (blue through red), with the biggest improvement at 500nm to 550nm (green) over “conventional” coating. The following illustrative graph shows how the color spectrum relates to wavelengths (as measured in nanometers):

The HD coatings allow the camera’s sensor to record more color information about blues, greens, yellows, and oranges for deeper, richer color rendition. The coatings also help reduce flare and ghosting for the production of rich, high-contrast images even against adverse lighting conditions, such as backlighting or strong side light. The DA 21, like the other DA Limiteds, is chiefly a contrast and color lens. It’s not particularly fast, it’s hardly the sharpest wide angle lens ever introduced, nor does it feature stellar control for vignetting or lens distortion. On the grounds pure measurements, its a good, but hardly a stellar lens. On the grounds of subjective perceptual evaluation, the DA 21 is capable of punching well above its numerical measurement weight. As Ricoh explains:

For the HD PENTAX-DA Limited lens, repeated performance evaluations using actual images were used to enable crystal-clear imaging with a deep richness and three-dimensional sensation going beyond mere numerical evaluation.

The emphasis on using actual images is the key here. Pentax, which is owned by Ricoh, has a long history of emphasizing actual images instead relying largely on numerical tests. In fact, this philosophy is so rooted into the company that they even go so far as to target specific colors. As Ricoh explains:

Even though it may not sound technically logical, it is the mission of PENTAX engineers to deliver the colors desired and favored by Pentaxians. Today, a camera is a cluster of high technologies, which continue to advance day by day. PENTAX believes, however, that, no matter how advanced technologies may become, image quality is always something perceived by the human eye, and is the product of human sensibility.

Such is the philosophy behind the DA 21. The lens itself, thanks to its pancake design and relatively slow aperture, features a fairly simply eight elements in five groups design:

The aspherical element, placed at the very back of the lens, is the only exotic piece of glass in the lens. What kind of images does this design produce? Let’s take a look, starting with some images shot at the sweet spot of the lens for edge to edge sharpness, f8. These are raw images processed to make fine prints. The first image shows a trail zig-zagging through the Del Norte Redwoods near the California coast:

Now let’s glance at a center crop:

And the corner crop:

This shows very good, if not quite outstanding performance. The center may be sharper than the corners, but the difference is difficult to discern even at the high magnification crops, and for practical purposes, is largely insignificant.

Next image:

Center crop:

Corner crop:

Fine performance here as well, with excellent contrast and color. It’s not only exhibits fine sharpness, but the tactile rendering of the detail, with rounded objects looking round against the background, and smooth objects looking smooth, is excellent as well.

Another sample:

Center crop:

Edge crop:

Corner crop:

What this series of images demonstrates is that resolution remains quite strong even out toward the edges. However, there seems to be some loss of resolution in the far corners. Nothing major or all that significant, but it is there all the same.

The online measurebators have complained that the DA 21 is not as sharp as a lens in its price class ought to be. I’ll have more to say of this a bit later. For the present, I will merely admit that the DA 21 is not quite as sharp as the very sharpest of Pentax’s DA Limiteds. As a point of reference, consider this image, shot by that “optical paragon,” (Mike Johnstone’s words), the HD DA 35 f2.8 Limited:

Now let’s look at the center crop:

As can be readily seen, this is somewhat sharper than the images shot with the DA 21 (look particularly at the first image of the set above, which has similar fine foliage detail). But it must be kept in mind that the DA 35 Limited is one of the finest APS-C lenses ever made. According to Johnston, it out-performed a Zeiss 28mm. So there’s no reason to be over dramatic about this. The DA 21 produces plenty of resolution, certainly enough for most practical purposes. In any case, if resolution is what you need, you’re probably better off shooting full frame lenses on a full frame camera. Nothing beats larger sensor size for gaining resolution.

Now, for those obsessed with wide-open performance, here’s an image shot at f3.2:

And here’s the center crop:

While obviously not as sharp as images shot at f8, this is not bad at all. The fine leaves to the right of the tree are blurry because of the narrower depth of field. But the ferns in the foreground have resolved quite nicely.

What about the bokeh of the lens? Of course, it’s only f3.2, but the lens does feature rounded aperture blades. Let’s look at a few samples, all shot wide-open:

Perhaps these backgrounds are a bit unfair, as they contain so much cluttered detail; even so, bokeh hardly seems to be the DA 21’s best attribute. Part of the problem is the f3.2: that’s not fast for a wide angle lens, particularly when matched with an APS-C sensor. Let’s just put it this way: if its background isolation and bokeh you’re looking for in a lens, the DA 21 is not for you. This is not an ideal lens for hand-holding in low-light or for isolating backgrounds with creamy bokeh. It just wasn’t designed for that. As I said earlier, it’s a color and contrast lens. That’s where it excels. The advantage of a slow aperture prime lens is that it uses less glass than zooms or faster primes. Less glass means less chances for flaring and ghosting, which, in turn, increases the odds of contrasty images with rich color. Photography is all about trade-offs. With the DA 21, you trade bokeh and fast aperture for small size, flare and ghosting control, and outstanding color and contrast.

Curiously enough, one of the differences between the HD version of the DA 21 and the original SMC version, other than coatings, is that in the newer lens, the aperture blades are rounded, which is supposed to improve the bokeh. Alas, this only works if you stop the lens down. But once you’ve stopped the DA 21 down, it becomes increasingly difficult to blur out the background, because the lens is just too slow. For this reason, some people are complaining about the rounded aperture blades in the DA 21. They don’t really improve the lens’ bokeh, but they do take away the ability to make very distinctive starbursts, which irregular blades help facilitate. With the rounded blades of the HD version, you have to stop the lens down to at least f16 to get even moderately decent starbursts, as the follow two images demonstrate:

I would contend that color and contrast is to landscape photography what bokeh is to candid portrait photography. The aforementioned Mike Johnston has even gone so far as to suggest that lens contrast, rather than sharpness, is the most important contributor to image quality:

In my opinion, lens contrast of fairly large image structures is a primary determinant of subjective optical quality in a camera lens.... But resolution of very fine structures seldom helps pictorial photographs much, and, in my opinion, is an overrated property where lens quality is concerned.

The DA 21 is often considered the weakest of Pentax’s DA Limiteds. Much of this, I suspect, comes, not from users of the lens, but as a result of measurebator reviews, particular the Lenstip.com travesty. In their review of the DA 21, the folks over at lenstip.com pontificated as follows:

There is another problem [with the DA 21]. Most standard zoom lenses offer us 21mm focal length. The purchase of a prime lens makes sense only when it offers something more than a zoom. This “something more” mainly consists of a better fastness or/and higher image quality. Here, unfortunately, such advantages are debatable because a lens like the Sigma 17-70 mm f/2.8-4.0 DC Macro OS HSM at 21 mm is not slower than the Pentax and the quality of images is the same, momentarily even better. What’s more, the Sigma is cheaper.

When the lenstip reviewer insists that the image quality of the DA 21 is similar to the image quality of the Sigma 17-70, he means that they exhibit comparable resolving cabablilities. What about other attributes of the lens? What about contrast and color rendition? That certainly must affect how an image looks to the observer. After all, when we examine images on flickr or in a gallery, we don’t normally pixel peep in order to determine minute and (largely) insignificant differences in resolution. But we definitely see the colors and the contrast. So why isn’t that included in the lenstip.com review? Our intrepid reviewer explains:

Even if sometimes it is difficult to find a rational reason of buying [the Pentax Limited lens] — like in the case of the DA 21 f3.2 model, tested here, which, optically, is bested by the cheaper Sigma 17-70mm – you don’t always take only purely rational aspects of a purchase into account. I don’t mean here that mythical image vividness which might be important to some users but I certainly don’t fall for it. I rather mean the pure joy of owning something truly original, untypical and made in a less cliché way than most of the equipment available nowadays on the market.

So color and contrast, or what the reviewer calls “mythical image vividness,” just doesn’t count! What’s important, rather, is how an image appears when viewed at 100% on a computer screen, along with the joy of owning something “original” and “untypical.”

The reviewers over at lenstip.com may define image quality any way they please. But if they insist that image quality is solely the product of the “numerical evaluations” of the lens, of which resolution of course forms the most important metric, than they are sadly deluded. Images are made to be seen, not measured, and those reviewers who know the measurements of the lenses they review but are clueless as to the value of the actual images such lenses create have very little to contribute to the discussion. We can safely ignore them.

The HD DA 21 f3.2 is primarily an image creating device. It produces photos of great clarity and contrast, with rich, vivid color and excellent rendering of tactile objects. While the DA 21 may not be the sharpest lens in the DA Limited drawer, it still features plenty of resolving power for most practical needs. And the lens itself, although entirely metal and glass, leaves a very small fingerprint in terms of weight and size. Even the hood is diminutive. Instead of the usual petal type of hood, that sticks out and takes up space, the hood for the DA 21 lies flat at the end of the lens, as so:

One odd feature of the DA 21 is that it has not one but two filter rings. If you take the hood off, you have access to a 49mm filter ring. If, however, you wish to keep the hood on, there’s also a 43mm filter ring below the hood. I’m not sure how practical that 43mm ring would be, if you wished to use a polarizer filter. But it’s there nonetheless for those who might think it useful.

To sum up: if you want a lens that provides superb color and contrast along with beautiful life-like rendering in a small, well-crafted package, the Pentax HD DA 21 f3.2 Limited will make an excellent addition to your kid. If, however, you need fast aperture and/or very high levels of resolution, it would be best to look elsewhere.

And now for some more images from the lens. First, at f5.6:

At f6.3

At f7.1:

At f8: