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Pentax DA* 300mm f/4 Lens Review
by David Rasnake -  5/29/2008

In the build-up to PMA 2008, Pentax announced that a pair of new telephoto primes – a 200mm f/2.8 and a 300mm f/4 – would be joining its high-end DA* (say: "DA star") series of lenses this spring. We took a look at the DA* 200mm f/2.8 back in March and were, to put it mildly, blown away by the price-to-performance ratio it offered.

Pentax DA* 300mm f/4

Two months later, its much anticipated larger brother, the Pentax DA* 300mm f/4 ED [IF] SDM, has made its way into our eager hands. With a lot to live up to, we were interested to see how things would play out for the latest high-dollar, long-reach offering from Pentax.


ERGONOMICS

Lens Mount

The DA* 300mm uses Pentax's current-generation KAF2 lens mount, which updates the basic K mount with communication contacts for basic lens function control, as well as a pair of contacts supporting the lens's SDM internal AF motor.

Pentax DA* 300mm f/4

Back compatibility with older DSLRs that use the first-generation KAF mount (the *ist cameras, for instance) as well as newer K digitals not running the latest firmware is ensured through the inclusion of a screw drive connection on the mount as well.

Feeling intrepid, we actually taped up the lens's KAF2-specific AF drive contacts to see if it would be possible to improvise an auto focus solution in the unlikely event that the internal focusing motor should fail, but while we succeeded in disengaging the SDM drive, we could never make the screw drive engage. Clearly there's some other communication voodoo at work in the KAF2 mount that lets the body know it's dealing with an SDM lens. There may yet be a simple field solution (short of reverting the firmware on your K10, that is) to accessing this backup drive function, however, which would be a boon for working photographers looking for AF system redundancy.

Design and Build Quality

Pentax has supported lenses similar in basic construction to the latest 300mm for several decades now, though the DA* version adds some key upgrades to this basic formula. As noted, the lens – like all of Pentax's DA* high-end optics – uses an internal supersonic focusing motor (a technology termed "SDM" by the manufacturer), as well as a traditional screw drive connection for focusing support on older Pentax digital bodies. Likewise, the new lens is sealed against water and dust, with a gasket at the lens mount providing an impervious connection to Pentax's weather-sealed DSLR bodies.

Pentax DA* 300mm f/4

A digital-only lens (like all of Pentax's DA offerings), the DA* 300mm f/4 shows a field of view equivalent to a 450mm lens in 35mm terms. Pentax's SP coating protects the front element. Internal construction features eight elements in six groups, with ED elements to compensate for chromatic aberration.

Pentax DA* 300mm f/4

With a 77mm front element and an overall length with the included hood attached totaling nearly a foot, light and inconspicuous are simply not in this long prime's vocabulary. The alloy-body lens weighs in at a hefty 2.8 pounds, creating some balance issues on even the larger Pentax K bodies without the additional counterweight of a battery grip.

Pentax DA* 300mm f/4

External construction is first rate, with an amply sized focusing ring providing the only moving part on the lens body's exterior (as there is obviously no zoom, and all focusing motion is internal). As with all of the DA* lenses we've looked at, the quick-shift focusing ring, which allows for on-the-fly transitions between auto and manual focus, doesn't feel as "connected" to the focusing element motion as a ring with a heavier throw would, but some users will undoubtedly appreciate a lens with such physically large glass that moves with such a light touch.

Pentax DA* 300mm f/4

The DA* 300mm features a distance scale, though there are no hyperfocal markings.

Pentax DA* 300mm f/4

A dedicated AF switch on the lens body can be used to disengage the auto focus system without taking your hand from the lens (though the camera-body switch is also active). As noted, quick-shift focus allows full-time manual focus override simply by turning the focusing ring.

Pentax DA* 300mm f/4

Pentax includes a large, thickly built lens hood with the DA* 300mm. It's a nice addition to this kit, with enough size to be useful in flare control. The interior of the hood is lined with felt, a Pentax-trademark filter notch allows easy access to polarizer and the like with the hood installed, and the unit can be reversed onto the lens barrel for storage when not in use.

Unlike the FA* 300mm f/4.5 it supersedes, the new DA* lens sports a built-in tripod collar. The smoothly machined collar is in keeping with the rest of the lens's thick metal construction. Detents at the customary positions (zero degrees and ninety degrees) provide firm, secure stops, and turning motion is smooth and well-damped. To make more a more comfortable grip space for hand-holding the lens, the base plate can be removed via a single slot-head screw (the wide slot of which appears to have been cleverly designed to perfectly fit a penny if you have no screwdriver handy).

All in all, it's hard to find much to pick it with the DA* 300mm's construction – even in light of its price and target market.

Handling

Although it's fair to say that the 300mm f/4 is compact and lightweight relative to what it is (compared to most constant aperture zooms covering out to 300mm, it's downright small), hand-holding the DA* can still be a bit of a chore. Of course, the integrated tripod collar makes flexible use of a monopod easy: not surprisingly, I found that my arms were happier and my shots were appreciably sharper with this arrangement. At this focal length, getting shutter speeds high enough to compensate for motion amplification without some external stabilization in place can often mean shooting at sensitivity or aperture settings that are less than ideal.

Pentax DA* 300mm f/4

As mentioned previously, if you do choose to work hand-held, throwing the battery grip on your K body is probably not a bad idea. The extra weight was more than offset in my experience by significantly improved balanced (the arrangement feels fairly front-heavy on a K10D body without the grip). Finding a grip position where your brace hand isn't interfering with the large focusing ring – which, if even slightly touched, will automatically clutch into manual focus mode – can also be a bit of a challenge, though removing the tripod base plate helps somewhat. An f/4 maximum aperture also means that the barrel is slightly narrower than many high-grade telephotos, flaring out slightly to its front element size of 77mm.

Pentax DA* 300mm f/4

Though it's a bit too tight for even close-in portraiture (unless you like standing a good distance from your subject) and it definitely won't replace a good 100mm macro, the DA* 300mm's minimum focusing distance of around 4.5 feet allows for some fairly tight work.

Pentax DA* 300mm f/4

Nice smoothness and good detail capture play well with this relatively close focus, allowing for interesting abstract compositions and perspective compression effects.

Pentax DA* 300mm f/4

The lens is a bit too large and conspicuous for my taste when it comes to urban shooting, though the distance it puts between you and your subject can make for some nice candids. Still, with its sizeable barrel and imposing overall appearance (especially with the hood attached), it's the kind of lens that gets you noticed a little more than may be preferable in an urban setting: spend too much time hanging around shooting photos with this piece of kit and you'd best be prepared to explain yourself to nervous onlookers.

Pentax DA* 300mm f/4

For sporting events, nature photography, or even a day at the zoo, however, the DA* 300mm's range is perfect, and its acceptable size and weight compared to many lenses in this class makes it an excellent choice.


PERFORMANCE

Auto Focus

The DA* 300mm f/4 uses Pentax's supersonic drive motor (SDM) technology to drive the AF system on compatible bodies. Coming from screw drive AF, the system feels significantly quicker (though at least some of this is unquestionably psychological) and is eerily quiet. Though there seems to be some variation from lens to lens regarding how much noise the SDM makes, our test unit was completely and utterly silent, with none of the squeaking noises we've heard from some other examples.

As mentioned, screw drive via the body's focusing motor is also supported, providing compatibility for older Pentax bodies. With either drive method, the lens's control ring doesn't move during focusing.

The 300mm's f/4 maximum aperture can make auto focus feel slow for a pro-grade lens in very low light, but in all but the darkest rooms our K10 test unit's 11-point AF system had no trouble driving the focusing motor smoothly and locking focus quickly.

Pentax DA* 300mm f/4

With subjects at or near infinity, the AF system did occasionally want to search the entire focus range between shots, but this tendency is nothing that a turn of the quick-shift focusing ring won't keep under control.

Manual Focus

Full-time manual focus can be selected either via the lens's onboard AF/MF switch or the camera body's control. Focusing ring travel is around 200 degrees from minimum focus to infinity, though the ring will continue to turn freely after the stop is reached.

Though it's not an f/2.8 lens, field of view through the DA* 300mm remains bright and crisp; I had no trouble securing accurate manual focus with this lens.

Image Quality

Excellent contrast and vibrant color reproduction in keeping with Pentax's history of building excellent primes are both apparent in using the DA* 300mm f/4. Compared to the sometimes weak colors and muddy contrast of many wide-range telephoto zooms in this price range, the DA* 300mm is a clear winner.

Pentax DA* 300mm f/4

Though it's a subjective evaluation for sure, bokeh tends to be quite smooth and pleasing to my eye as well, with soft, swirled backgrounds bringing out the contrasty pop of foreground subjects – even against typically intrusive backdrops.

Pentax DA* 300mm f/4

Showing some evidence of its presumed lineage, the DA* 300mm exhibits a closer connection with the warmer tint associated with classic Pentax glass than the cooler, more modern image tone seen in the latest ground-up designs. This look plays to the K10D's strengths, emphasizing the film-like texture and natural, slightly warm look of the camera's default JPEGs.

Pentax DA* 300mm f/4

Unlike the FA* 300mm, which was known for fairly uniform sharpness across the board, the DA* 300mm is a bit of a roller coaster ride in this regard. In examining 100-percent crops from our test chart shots, both edge and center are noticeably soft at f/4.

Pentax DA* 300mm f/4
Edge, f/4

Pentax DA* 300mm f/4
Center, f/4

Pentax DA* 300mm f/4
Edge, f/8

Pentax DA* 300mm f/4
Center, f/8

Pentax DA* 300mm f/4
Edge, f/16

Pentax DA* 300mm f/4
Center, f/16

Though our standard array of test-chart crops (maximum aperture, f/8, and f/16) doesn't show it, our testing suggests that sharpness improves considerably at f/5.6, falls off a bit to f/8, and then improves again to an apparent maximum somewhere around f/11.

In actual use, f/4 proved to be less distractingly soft than it looks in a controlled test:

Pentax DA* 300mm f/4

The DA* 300mm also shows the slightest hint of pincushioning, though unless you're shooting subjects with perfectly true lines you'll be hard pressed to pick it out. In equal measure, color fringing is well controlled with this lens: beyond the occasional appearance at f/4, test shots suggest the DA* to be basically fringe-free. Likewise, a faint trace of vignetting at f/4 was the closest this lens came to showing darkened corners in any of our test shots.

The lens can be prone to ghosting and the accompanying wash-out when shooting into the sun, though the large hood helps keep off-axis light from causing issues. I had trouble inducing flare in any significant measure, even when pointing the front element directly toward strong light sources.


CONCLUSIONS

Pentax shooters have been waiting a long time for this lens: with precious little other high-grade glass available in this focal length (especially with AF), and basically no other widely available primes, if you're wanting a new fixed focal length lens in this range with auto focus, this is your choice. The fact that it's a pretty good one is probably icing on the cake if you're a diehard Pentax shooter, and for birding, general nature photography, or even sports work, the DA* 300mm is competent and reasonably compact.

If it's a pretty good lens, though, the latest DA* certainly didn't make the impact around here that it's smaller brother did. Whereas we came away feeling that the DA* 200mm f/2.8 was a superior lens for its price, size and weight, the DA* 300mm f/4 is merely a good one, all things considered. A slightly slow maximum aperture (by pro-glass standards) combined with some visible softness across the frame at f/4 will be a thorn in the side of persnickety users (though I rarely found myself unsatisfied with the sharpness in even 8x10 prints at maximum aperture).

While it may not be the near-perfect tool that the DA* 200mm proved to be, the 300mm variant largely lives up to the hype – filling an important niche for Pentax and doing so in a nice package for a fair price.

Pros:

Cons: