The HD D FA 150-450mm F4.5-5.6 ED DC AW ($2,499.95) is the first full-frame telezoom lens that Pentax has released in quite some time. It's well built, sharp through most of its range, sealed against dust and moisture, and should appeal to both K-1 owners, as well as APS-C photographers looking for a lens with long reach for sports and wildlife use. But sharpness drops a bit at 450mm, the focus motor is on the slow side, and the asking price is much higher than you'd expect. It's worth a look, especially if you often shoot in inclement conditions. But there are less expensive alternatives available, including the Sigma 50-500mm F4.5-6.3 APO DG OS HSM ($1,659).

Design

Despite covering a modest 3x zoom range, the 150-450mm ($1,996.95 at Amazon) is a big, heavy lens. It measures 9.5 by 3.7 inches (HD) at its shortest, features a design that extends the lens barrel when zoomed, requires the use of big 86mm front filters, and weighs a hefty 4.4 pounds. Compare this with a similar lens for the Canon system, the EF 100-400mm f/4.5-5.6L IS II USM ($2,199.00 at Amazon) , which covers a longer zoom range, but measures just 7.6 by 3.7 inches and weighs 3.6 pounds.

The lens features a black barrel, with metal and polycarbonate components, finished with a green accent ring. Build quality is excellent, with an o-ring seal at the mount joining several internal seals to keep dust and moisture out of the lens and camera both. Like most Pentax SLRs, this is an all-weather lens.



The zoom ring, covered in textured rubber, occupies a large portion of the barrel, and is marked at 150, 200, 300, 400, and 450mm. A lock switch can keep the lens set to its 150mm position, so it doesn't creep out when hanging at your side.



There are several other switches on the barrel. They control the focus mode, allow you to set a limit over which the autofocus will hunt, and work with a pair of buttons to save a preset focus distance, which can be racked back to with the press of a button. These functions help to compensate for a DC autofocus motor that's on the slow side—you'll certainly miss some shots with the 150-450mm that a lens with a quicker focus motor would be able to capture.



The 150-450mm ships with a detachable tripod foot. It attaches to the rotating collar, so you can easily switch between portrait or landscape orientation when working with a tripod or monopod. If you're trying to cut down on weight, the foot can be removed.



A manual focus ring sits toward the mount. It's covered in the same textured rubber as the focus motor. You can use it to override automatic focus acquisition at any time, regardless of camera focus settings. The lens can lock onto targets as close as 6.6 feet (2 meters), for about 1:4.5 magnification at its shortest focus distance and longest zoom setting. That's not as good as the Sigma 50-500mm, though, which can magnify subjects at 1:3.1.



Image Quality

I used the full-frame K-1 and Imatest to evaluate the 150-450mm's optical quality. It passes muster on the sharpness test at 150mm f/4.5, notching 2,466 lines per picture height, better than the 2,200 we look for in an image. Sharpness is even from edge to edge, the mark of an excellent performer. Image quality improves as you stop down, hitting 2,698 lines at f/5.6, and peaking at 2,726 lines at f/8. Clarity drops slightly at f/11 (2,688 lines), and more so at f/16 (2,533 lines) and f/22 (2,478 lines).

At 300mm f/5.6 the lens scores 2,235 lines, a bit less than at its widest angle, but still acceptably crisp. Stopping down to f/8 improves quality significantly, to 2,703 lines, and image quality is strong at f/11 (2,664 lines) and f/16 (2,631 lines). It drops to 2,451 lines at f/22.



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There's another drop in performance at 450mm, with the lens falling short of our sharpness cutoff. At f/5.6 it shows about 1,900 lines, and improves only marginally at f/8 (1,999 lines) and f/11 (2,077 lines). We didn't get a truly crisp image until f/16 (2,450 lines) and f/22 (2,525 lines). At wide apertures edges lag behind the center, but performance is strong throughout the entirety of the frame at f/16 and f/22.



Pincushion distortion is constant throughout the zoom range. At 1.2 percent, though, it's a modest amount, giving straight lines the appearance of a slight inward curve. Likewise, illumination is fairly even, with the lens showing only about a -1.2EV drop at the corners at its widest aperture. That's noticeable, but just barely, in real-world use. If you shoot in JPG format your camera can compensate for both distortion and illumination automatically. Raw shooters can compensate for both issues using a Lightroom ($9.99/Month at Adobe) lens profile.



Conclusions

The Pentax HD D FA 150-450mm F4.5-5.6 ED DC AW is a big beast of a telephoto lens that doesn't cover as long of a range as you'd expect by looking at it. It's heavy, but that's in no short part due to its exceptionally sturdy build quality. It delivers sharp results through a good portion of its zoom range, but image quality takes a hit at 450mm, requiring you to stop down significantly to get the best results. Add in a focus motor that's on the slow side (especially for a lens that's going to be pointed at moving targets) and a high asking price, and you have a zoom that's hard to recommend highly. There are not that many third-party alternatives available for Pentax SLRs, but the obvious choice is the Sigma 50-500mm F4.5-6.3 APO DG OS HSM. We haven't tested it yet, but the lens is significantly less expensive and covers a longer range, extending both wide-angle and telephoto coverage.

Pentax HD D FA 150-450mm F4.5-5.6 ED DC AW 3.0 See It $1,996.95 at Amazon MSRP $2,499.95 Pros Sharp through most of range.

Top-end build.

Weather-sealed design.

Focus limiter function.

Includes tripod collar. View More Cons Slow focus.

Heavy.

Very expensive.

On the soft side at 450mm.

Some distortion. View More The Bottom Line The Pentax HD D FA 150-450mm F4.5-5.6 ED DC AW is a solidly-built telezoom lens, but it's heavier and pricier than others in its class.

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