The Tamron SP15-30mm f/2.8 di VC USD is a superb ultra-wide zoom that you will have come across if you are looking for one in the recent past. (Opens in new window). Tamron's wide-angle wonder for Pentax cameras doesn't exist, at least not under its own brand. Pentax HD D FA15-30mm F2.8 ED SDM WR (1,449.95) is a rebadged Tamron zoom. It does not include the stabilization system which Pentax integrates into their cameras rather than the lenses. Even paired with full-frame K-1 ($1,599.00 Amazon), it is a heavy zoom. However, this zoom can be used to great effect and will make a good choice for Pentax photographers looking for an extremely wide zoom.
Design
$1546.95 Amazon 15-30mm (Opens in new window), measures 5.7 by 3.0 inches (HD), and weighs 2.33 pounds. It has a large, bulky front that prohibits lens filters. The base is completed by an o-ring. 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. The zoom is controlled by a rubberized, large focus ring that has a tactile texture and can be easily gripped. The focal lengths are marked in mm at 15, 20, 24, 24 and 30.
The mount is complemented by a narrower, more precise manual focus ring that sits close to it. It has the same texture. You can adjust the focus settings as you wish and it can rotate at all times, even if autofocus is enabled. The current distance to focus is displayed in a window. It can be shown both in feet and meters. An internal motor drives the focus, moving the glass within the lens quickly to obtain a lock. It's also quiet.
The focal length of the 15-30mm is between 11 inches (28cm), and infinity as measured by the sensor. You can focus close to the front elements, capturing images of subjects with large backgrounds and 1:5 magnification for 30mm.
For our regular round of performance testing, I combined the 15-30mm and the 36MPK-1. Imatest (Opens in new window) at 15mm f/2.8 shows that the lens scored 2,311 lines per image height in a center-weighted sharpness testing. This is better than we would like to see in an actual image with 2,200 lines. The performance is excellent throughout the frame and even around the edges. The scores increase to 2,749 lines at f/4, while it stays steady at 2,763 line at f/5.6. The best results are at f/8 (2.921 lines), f/11 (2.905 lines), before it loses a little clarity at f/16 (2.744 lines) or f/22 (2.422 lines).
Image quality is very good at 24mm. The resolution at f/2.8 is 2,728 lines with strong performance across the entire frame. The image quality remains steady at f/4 (2.724 lines), 2:753 lines, f/5.6 (2.753 lines), 8 (2.896 lines) and 11 (2.907 lines). A slight drop is seen at f/16 (2.753 lines), f/22 (2.424 lines) and f/11 (2.907 lines).
At 30mm, the story is almost identical. 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. The fidelity drops to f/22 (2.418 lines).
At 15mm, barrel distortion can be noticeable. This lens has a 4.5 percent distortion, giving images a slight fish-eye appearance. As you zoom distortion changes. It is absent at 20mm, but it becomes pincushion distortion between 24mm and 30, respectively.
Also, corner dimness can be seen. The corners are 2.5EV behind the center at 15mm f/2.8. This deficit is reduced to -1.6EV when you open the aperture wider and less than 1EV for narrower apertures. The corners fall by -1.8EV between 21mm and 30, f/2.8. This is reduced to -1EV at the f/4 aperture and less than one stop for narrower apertures. If you are shooting JPG, both distortion and illumination can be corrected in camera. Raw capture can be corrected using the lens profile in Lightroom.
Conclusions
The Pentax clone, like the Tamron 15-30mm is large and bulky. This is normal for wide-angle zooms. The 15-30mm has a f/2.8 rating throughout its zoom range, which captures sharp images from every edge. Although it does have some distortion and the corners and edges can be dimmed at f/2.8 both these performance issues are easily fixed by software. The Pentax HD D FA15-30mm F2.8 ED SDM WR, a Pentax full-frame Pentax camera with a wide zoom is able to provide an exceptional performance.
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