The Opteka mirror lens is incredibly compact and lightweight. Using an advanced reflex design, this is a mirror lens that is ideally suited for wildlife and sports photography. It has a fixed aperture of f6.3. Opteka mirror lenses incorporates advanced computer designed optics and the latest in multi-coating techniques. The process of multi-coating assures virtually flare free photographs even under adverse lighting conditions resulting in crisp high contrast pictures with full color fidelity.When combined with the T-mount to fit your camera system, this mirror lens mounts to camera and works on both "full frame" cameras as well as the "APS-C" style digital SLR cameras. T-Mounts are available for all the digital SLR systems, as well as for C-mount systems. However, in every case the fixed f/6.3 aperture is not communicated to the camera body. As such, you can use the lens in "M" manual exposure mode or "A" aperture-priority mode only. This lens has a broad diameter and stocky build, making it a bit easier to handle than a normal refractor lens. It also has a much different rendering of out of focus areas than a normal lens; highlights will be doughnut-shaped rings with more saturation and contrast on the edge of the ring than on the center.The included Opteka 2X Teleconverter effectively doubles your zoom converting this lens to a 500mm / 1000mm Super Telephoto! Please note that this is a manual lens. You will need to set your camera to manual mode. Specifications Filter Size: 95mm front, 34mm rear f/Stop Range: f/6.3 (fixed) Minimum Focus Distance:6.6' (2.0 m) Angle of View: 4.1Deg x 2.7Deg (WxH) Groups/Elements: 6/7 Length: 4.7" (120mm) Maximum Diameter: 3.9" (98mm) Weight: 1.55 lbs (705g)Included Items ~ Opteka 500mm f/6.3 Telephoto Lens ~ Opteka 2x Teleconverter ~ T-Mount Lens Adapter ~ 47th Street Photo Micro Fiber Cleaning Cloth