This is a digital reincarnation of Pentax's unique, full-frame, 17-28mm f/3.5-4.5 fisheye zoom of the mid-1990s. It's the only current zooming fisheye and the first Pentax lens to use a newly developed SP (Super Protective) coating on its front element. As with most fisheyes, the front element of this 10-17mm (a 15-26mm equivalent, due to the 1.5X 35mm lens factor on Pentax DSLRs) bows out in front of the barrel, leaving its arched glass surface unusually exposed. Pentax claims that its SP coating, applied using a new evaporation process, improves surface resistance to water and finger oils, making it easier to clean. Still, beware of scratches!
HANDS ON: Marked by the green ring of the Pentax DA series, this lens is remarkably light and compact compared to fisheyes of yore. Except for that front element, it resembles Pentax's 30mm "normal" DA lens. With all-metal construction (even its cap is aluminum), it has standard ribbed and rubberized zoom and focusing collars. The latter sports adequately legible blue (feet) and white (meters) distance scales, but is narrow. Both collars turn with well-damped actions. The lens also uses Pentax's Quick-Shift focusing system for instant shifting between auto and manual focus. Like Pentax's full-frame fisheye, it won't accept front- or rear-mounted filters -- the price you pay for compactness and a 180-degree field of view.
IN THE LAB: At its uniform close-focusing distance of 5.25 inches, maximum magnification ratios ranged from 1:4.6 at 10mm to an impressive 1:2.6 at 17mm. Due to the unusual nature of this lens, we were unable to perform optical bench or wall-target tests, including the SQF and DxO Analyzer distortion and vignetting tests. You can expect a fair amount of both -- it's a fisheye, after all.
CONCLUSION: This lens offers plenty of options for creativity, thanks to both the huge barrel distortion in its ultrawide angle of view (at 10mm) and the unusual perspective distortion when subjects are close and the background distant. The earlier 17-28mm fisheye is still widely available at a price $100 less than this new $500 DA zoom. Sound tempting? Don't forget that the earlier lens becomes a 26-42mm equivalent on an *ist DSLR -- not your traditional fisheye view, but a midrange zoom with overflowing barrels of distortion. This one, on the other hand, is the real thing.