Pentax smc DA* 55mm 1:1.4 SDM review

The Pentax smc DA* 55mm F1.4 SDM is one of the company's more recent creations, announced in September 2008. Unlike the 50mm F1.4 primes which have appeared in the past year or so from the likes of Sigma and Nikon, this lens's DA* designation indicates that it has been specifically designed for the APS-C sensor format (as opposed to full frame 35mm). This in turn explains the slightly longer-than-usual focal length, which gives an 82.5mm-equivalent angle of view; Pentax is marketing the lens as purpose-designed for portrait work, and the spiritual successor to the company's film-era FA 85mm f/1.4. The result is a slightly longer working distance when compared to a conventional 50mm prime on APS-C, which gives a more flattering perspective for head-and-shoulder portraits.

The optical design reflects the lens's intended purpose - out goes the old 7 element / 6 group, unit-focusing double-Gauss type design of the FA 50mm F1.4, replaced by an altogether more complex 9 element / 8 group construction, which incorporates a 'floating focus' mechanism for improved performance at close distances. The 9-bladed diaphragm uses curved blades to maintain a circular aperture on stopping down, which should provide a more natural rendition of out-of-focus backgrounds. An array of coating technologies is used to cut down on flare, including a new 'Aero-Bright' coating to reduce internal reflections and 'Super Protect' coating on the front element. The lens also incorporates Pentax's ultrasonic-type 'Supersonic Drive Motor' for silent and fast autofocus, with 'Quick Shift' manual override. However there's no screw-drive coupling to the camera body, which means that the lens won't autofocus on bodies older than the K10D (i.e. the *ist series, K100D and K110D) which lack the contacts to power the SDM motor.

Also on the list of goodies is dust- and weather-sealed construction, using an array of 'O'-rings to protect against dust and water; this makes the lens an ideal match to Pentax's range of similarly weatherproofed bodies such as the K10D, K20D and the new K-7. However this all comes at a price, and a steep one at that - more than twice as much as the old 50mm F1.4. So does the new lens offer a sufficient improvement in image quality to justify the outlay?

Headline features

• 55mm focal length; fast F1.4 maximum aperture
• Built-in ultrasonic-type SDM focus motor with 'Quick-Shift' manual focus