The Pentax HD DA 16-85mm f/3.5-5.6 ED DC WR ($649.95) is one of several all-weather zoom lenses available for the company's APS-C SLR system. It's a solid option for shooters who want a longer range than a basic 18-55mm kit lens, with wider coverage and better image quality than you get with the SMC DA 18-135mm f/3.5-5.6 ED AL (IF) DC WR. It doesn't offer a significant improvement in light gathering, however, which is why we give preference to a third-party option, the $500 Sigma 17-70mm F2.8-4 DC Macro HSM, even though it omits protection from dust and moisture.

Design

The 16-85mm is a squat lens, but one that extends when zoomed beyond its widest setting. It measures 3.7 by 3.1 inches (HD) at its shortest, and extends to about 6 inches when set to the 85mm position. It weighs about 1.1 pounds, supports 72mm front filters, and ships with a reversible lens hood and front and rear lens caps.

You can only get it black, unlike the smaller, similarly sealed HD DA 20-40mm F2.8-4 ED Limited DC WR zoom, which is available in black or silver. The 16-85mm is polycarbonate, rather than metal, with the only color coming from a red accent ring behind the front element.

There's a very narrow manual focus ring toward the base, covered in a textured finish so you can identify and turn it with ease. The lens offers full-time manual focus override, even when the camera is set to autofocus. The zoom ring is finished in a similar texture, and occupies almost the entirety of the barrel. It has set marks at 16, 24, 35, 50, and 85mm.

You can mount the lens to a full-frame camera; Pentax has one in its current lineup, the K-1. But expect a serious dark vignette around your frame, as the lens is only designed to cover the smaller, APS-C sensor that Pentax uses in most of its cameras. Its field of view matches that of a 24-128mm full-frame zoom.

You won't find any toggles or switches on the barrel. There's no built-in stabilization—Pentax puts that feature in camera bodies rather than lenses. There's also no focus limiter, which isn't a big deal. The 16-85mm focuses as close as 13.8 inches, which gives it a decent 1:3.8 magnification ratio at its closest focus distance and 85mm setting. There's no need to separate close focus and distant focus ranges with this lens.

Image Quality

I tested the 16-85mm with the 24MP Pentax KP. At 16mm f/3.5 the lens scores 1,981 lines per picture height on Imatest's standard center-weighted sharpness test. This is better than the 1,800 lines we want to see at a minimum; it's a good score, but not an excellent one. The center area of the frame is excellent, however, at 2,381 lines, but you lose resolution as you move away from it. The mid parts are okay, at 1,879 lines, but edges are noticeably soft, showing just 1,461 lines.

Narrowing the aperture improves image quality. The lens scores 2,339 lines on average at f/5.6, with performance that is as good or better than the average through most of the frame, and edges that are a crisp 2,014 lines. You'll get the best 16mm results at f/8—the average score is an excellent 2,448 lines and performance is relatively even from center to edge. Narrowing the f-stop further reduces clarity; the lens shows 2,350 lines at f/11, 2,160 lines at f/16, and a mere 1,806 line at f/22.

The maximum aperture has already narrowed to f/4.5 at the 35mm position. Resolution is strong through most of the frame, showing about 2,152 lines on average, but edges are soft at 1,522 lines. Stopping down to f/5.6 nets better results at the edges (1,956 lines) and overall (2,368 lines). Again, at f/8 you get excellent, even performance from edge to edge, 2,438 lines on average, and you don't lose much by stopping down to f/11 (2,374 lines). You can get decent results at f/16 (2,202 lines), but the lens loses something at f/22 (1,921 lines).

At 85mm f/5.6 the lens has lost a bit of resolution, showing 1,963 lines. The center is very sharp (2,345 lines), with mid parts that hit the average and very soft edge performance (1,231 lines). You get better overall resolution at f/8 (2,197 lines), with even performance through most of the frame, but edges that are still a bit soft (1,673 lines). The best edge-to-edge quality is achieved at f/11 (2,274 lines), and f/16 is quite usable (2,145 lines). Skip f/22 (1,846 lines), unless you need to stop down that far for depth of field or a long exposure image.

There's some visible distortion, although if you shoot in JPG format you can set your camera to remove it automatically. You get about 3.3 percent barrel distortion at 16mm, curving straight lines outward. At 35mm lines are properly straight, but you get about 1.1 percent pincushion distortion, which curves lines toward the center, at 85mm. If you capture Raw images and process them in Lightroom CC, you can remove distortion using the built-in lens profile.

There's also a noticeable vignette, but only at the widest angles. When shooting at 16mm f/3.5, the corners lag behind the center by 2.8 f-stops (-2.8EV). The deficit is cut to -1.6EV at f/5.6, and is still noticeable at f/8 (-1.2EV). At narrower settings it's slighter, about -1.1EV. You can compensate for the vignette using in-camera correction, or remove it using Lightroom with the same lens profile that corrects distortion. At longer focal lengths the vignette isn't apparent.

Conclusions

The Pentax HD DA 16-85mm f/3.5-5.6 ED DC WR delivers decent image quality and covers a good amount of range. At its widest it captures more of a scene than standard kit lenses, and its sealed design means you can use it in rough weather along with most Pentax SLRs. It's not without its flaws, though—its $650 price is high for an f/3.5-5.6 design, and edge performance lags behind competitors. If you can sacrifice protection from weather, and a little bit of range, the Sigma 17-70mm F2.8-4 DC Macro HSM is a better overall performer, and available for less.

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