The Sigma 17-50mm f/2.8 EX DC HSM Zoom Lens for Pentax DSLRs W/APS-C Sensors is an incredibly versatile, lightweight, and compact lens designed specifically for Pentax digital SLR cameras with APS-C size sensors. The lens has a fast f/2.8 maximum aperture throughout the entire zoom range. It features a construction of 17 elements in 13 groups with glass that corrects for flare, ghosting and all types of aberrations. It produces high contrast and sharp images throughout the zoom range even at its maximum aperture. This lens is also equipped with Sigma's Hyper-Sonic Motor (HSM) which provides for fast and quiet autofocusing. The Sigma 17-50mm f/2.8 is ideal for many photo opportunities particularly landscapes and portraits, but with its wide focal range and a close focusing distance down to 11" (28cm) you can capture images with unique perspectives. It will quickly become one of the most important lenses in your gear bag. Note: Vignetting will occur if the lens is used with digital cameras with image sensors larger than APS-C size or 35mm SLR cameras. This lens is for use with Pentax digital cameras with APS-C size sensors only. 1The DC designation on the barrel means that this is a special lens designed so that the image circle matches the smaller size (APS-C) of the image sensor of your digital SLR. Its specialized design gives this lens the ideal properties for digital cameras, including a compact size and lightweight construction.Constructed with 17 elements in 13 groups, it features FLD ("F" Low Dispersion) glass which is the highest level low dispersion glass available with extremely high light transmission. This glass has a performance equal to fluorite glass which has a low refractive index and low dispersion compared to current optical glass. FLD glass offers superior optical performance, equal to fluorite, at an affordable price.Its HSM (Hyper-Sonic Motor) ensures a quiet & high-speed auto
