A truly long-reaching lens designed for Pentax K-mount cameras, the 500mm f/4.5 EX DG APO HSM from Sigma is a super telephoto characterized by its relatively fast maximum aperture and apochromatic optical design. Employing a pair of Extraordinary Low Dispersion glass elements to reduce chromatic aberrations and color fringing, this lens produces notable clarity and color fidelity throughout the aperture range. A Super Multi-Layer Coating has also been applied to realize greater contrast when working in backlit or difficult lighting conditions.Complementing the optical attributes, this lens also sports an internal focusing design, along with a Hyper Sonic Motor, to deliver fast and quiet autofocus performance, and a manual focus clutch allows for quick switching between auto and manual focusing positions. Benefitting handling and use, a rotating tripod collar is featured for increased stability and easier switching between horizontal and vertical shooting orientations. Additionally, this lens accepts 46mm drop-in style filters via the included holder, and both UV and circular polarizer filters are included.Prime super telephoto 500mm f/4.5 lens is designed for full-frame Canon EF-mount DSLRs, and can also be used on APS-C models where it provides an 800mm equivalent focal length.Sporting an apochromatic design, two Extraordinary Low Dispersion (ELD) glass elements are used to reduce chromatic aberrations and color fringing throughout the aperture range in order to produce greater clarity and color fidelity.A Super Multi-Layer Coating has been applied to minimize ghosting and flare when working in strong lighting conditions.The integrated HSM (Hyper Sonic Motor) realizes quick and quiet autofocusing, which is further complemented by an optimized AF algorithm to produce smoother focusing performance.Internal focusing design limits the overall length of the lens during operation for more intuitive, controlled handling as well as faster performance.A manual focus clutch lets you slide the focusing ring back or forth to quickly switch between manual and autofocus modes.Nine-blade diaphragm contributes to a pleasing bokeh quality when working with selective focus and shallow depth of field techniques.A fixed, rotating tripod collar offers increased stability when working from a tripod as well as intuitive switching between horizontal and vertical shooting orientations.A rear drop-in slot enables the use of 46mm drop-in filters via the included filter holder, and both UV and circular polarizer filters are included.Compatible with optional APO Tele Converters to further extend the reach of this super telephoto lens