Rokinon 500M-PK 500mm F8.0 Mirror Lens for Pentax 500mm Manual Focus Mirror Lens with a F8.0 fixed aperture 7 elements in 6 groups Filter size: Rear 30.5 mm/ Front 72mm Minimum focusing distance of 5.6 ft Includes ND-2X, ND-4X and Skylight rear-mount filters, lens caps, lens pouch, instruction manual, and 1 year Rokinon warranty