The Pentax 55mm f/1.4 DA* SDM Autofocus Lens is a compact and bright short-telephoto lens of the highest order, made exclusively for Pentax digital SLR cameras. In a stocky housing ready for harsh conditions, you'll get a bright f/1.4 aperture-worlds away from the experience you're used to with more common zooms-that opens up new creative doors to you as a photographer.
This lens was born to shoot between f/1.4 and f/2.8, and comes with a 9-bladed aperture diaphragm which shows up as perfectly round when you stay between f/1.4-2.8. Shoot dramatic portraits with bright point light sources behind the subject, and you'll be dazzled with lovely diffuse, circular out-of-focus highlights that make everybody look better. Beyond portraits, this lens works well any time you would use a moderate telephoto focal length.
The focusing system of this lens is SDM only; there is no screw on the rear of the lens barrel to have the AF driven by a body-based motor. This allows the lens to move incredibly quick, driven by an internal motor and with the Quick-Shift system providing manual override capacity to you any time you want it with no buttons to switch, but you'll need a Pentax body which allows SDM autofocus (all current Pentax bodies support SDM, but the *IST series does not).
Note:
Does NOT provide autofocus upon non-SDM-enabled Pentax cameras.
Brilliantly-sharp portrait lens which gathers plenty of light
Completely-rounded aperture diaphragm from f/1.4-2.8 for beautiful out-of-focus highlights
Speedy SDM autofocus motor provides fast, silent response with Quick-Shift full-time manual override
Pentax's unique SP water and dirt-repelling coating on both external surfaces
Pentax's "Aero Bright" internal lens yields high transmissivity and reduced flare
Dust and moisture-resistant housing
Essentially equivalent to an 82.5mm f/1.4 lens upon APS-C Format cameras