PROS
- Quite sharp.
- Fixed f/2.8 aperture.
- Integrated hood.
- Ultra-wide field of view.
- Strong close focus capability.
- Weather-sealed design.
CONS
- Barrel distortion at widest angles.
- Dim corners. Bulky.
- Omits filter thread.
BOTTOM LINE
The Pentax HD D FA 15-30mm F2.8 ED SDM WR is a huge lens, but one that covers an ultra-wide field of view with excellent sharpness, even at f/2.8.
Design
The 15-30mm$1,446.95 at Amazon measures 5.7 by 3.9 inches (HD), weighs 2.3 pounds, and has a huge, bulbous front element that precludes the use of lens filters. An o-ring sits at the base, completing the weather sealing that you get with a Pentax SLR. A modest lens hood is built in—and while I didn’t see any flares or ghosting when shooting with the Pentax version of the lens, they did appear occasionally when shooting with the Tamron, so be mindful of where the sun is when shooting at 15mm.
The lens doesn’t have any control switches—image stabilization isn’t included, as that feature is built into Pentax SLR bodies. Zoom is adjusted via a large, rubberized focus ring, finished in a texture that’s easy to grip. Focal length is marked at 15, 18, 20, 24, and 30mm.
A narrower manual focus ring sits closer to the mount, finished in the same texture. It can turn at any time, even when the camera is set to autofocus, so you can make fine adjustments to focus as desired. A window shows the current focus distance, marked in both feet and meters. Focus is driven by an internal motor that’s quick to move the glass inside the lens to acquire a lock. It’s also quiet.
The 15-30mm focuses from 11 inches (28cm) to infinity, as measured from the image sensor. This allows you to focus very close to the front element, getting up close and personal with subjects to capture images with a vast background, and delivering 1:5 magnification at 30mm.
Image Quality
I paired the 15-30mm with the 36MP K-1 for our standard round of performance tests. At 15mm f/2.8, Imatest shows that the lens scores 2,311 lines per picture height on a center-weighted sharpness test, better than the 2,200 lines we want to see in an image. Performance is strong throughout the frame, even at the edges. At f/4 the scores improves to 2,749 lines, and it remains steady at 2,763 lines at f/5.6. You get the best results at f/8 (2,921 lines) and f/11 (2,905 lines) before losing a bit of clarity at f/16 (2,744 lines) and f/22 (2,422 lines).
At 24mm image quality remains very strong. At f/2.8 the resolution is 2,728 lines, with strong performance from edge to edge. Image quality is steady at f/4 (2,724 lines), f/5.6 (2,753 lines), f/8 (2,896 lines), and f/11 (2,907 lines). There’s a modest drop at f/16 (2,753 lines) and f/22 (2,424 lines).
The story is about the same at 30mm. The lens manages 2,698 lines at f/2.8, improves to 2,812 lines at f/4, and gets better as you stop down further—2,868 lines at f/5.6, 2,959 lines at f/8, 2,988 lines at f/11, and 2,936 lines at f/16. There’s a drop in fidelity at f/22 (2,418 lines).
Barrel distortion is a noticeable issue at 15mm. The lens shows about 4.5 percent, which gives images a mild fish-eye look. As you zoom distortion changes. At 20mm there is none, and it gives way to pincushion distortion at 24mm and 30mm.
Corner dimness is also noticeable. At 15mm f/2.8 the corners lag behind the center by about 2.5 stops (-2.5EV), a deficit that’s cut to -1.6EV at f/4 and is less than -1EV at narrower apertures. At 21mm and 30mm f/2.8 the corners drop by -1.8EV, which is cut to -1EV at f/4 and less than a stop at narrower apertures. Illumination and distortion can both be compensated for in-camera if you shoot JPG. If you opt for Raw capture you can correct for it using a lens profile built into Lightroom.
Conclusions
As is the case with the Tamron 15-30mm, the Pentax clone is a big, bulky lens. But that’s par for the course with wide-angle zooms, and when you consider that the 15-30mm is rated at f/2.8 through its entire zoom range and captures images that are sharp from edge to edge, the size is understandable. It does show a bit of distortion, and corners and edges are dim at f/2.8, but both of those performance aspects are easily compensated for using software tools. So if you’re in want of an ultra-wide zoom for your full-frame Pentax, you’ll be happy to know that the Pentax HD D FA 15-30mm F2.8 ED SDM WR is an excellent performer.
Sourse: pcmag.com
