The Pentax SMC DA* 55mm F1.4 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.
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 35mm SLR cameras
Standard in focal length, but excellent in quality, the smc Pentax DA Star 55mm for Pentax digital SLR cameras is incredibly fast and offers outstanding depth of field control. And with its weather-resistant construction, it?s versatile enough for all types of shooting conditions.
* Portrait, still life, low light photography, weddings
"Quick Shift" focusing
Only compattible with SDM enabled cameras