The Opteka mirror lens is incredibly compact and lightweight. The image coming through the lens is bounced off of mirrors before going to the image sensor. This allows the lens to be much shorter than it would need to be without the mirrors. This lens has no diaphragm and is normally used with adjusting the shutter speed to reduce light. Using an advanced reflex design, this lens is perfect for the professional and amateur photographer alike. Using a 2x tele-converter with a 500mm will effectively increase the focal length to 1000mm. A lens set to f/6.3 will now be f/12.6. It's an extremely powerful telephoto zoom lens with the versatility that you need. This lens is great for the wildlife or nature photographer who wants to be hidden while taking photos of the subject. When combined with the included T-mount to fit your camera system, this telephoto works on both "full frame" cameras as well as the "APS-C" style digital SLR cameras. 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.<br><br> Bright sunlight and a sturdy monopod or tripod is recommend when using this lens.<br><br> Specifications<br> Elements/Groups: 7/6<br> Focus Modes: Manual Focus<br> Minimum Focus: 6.6' (2.0 m)<br> Angle of View: 4.1 to 2.7 Degrees<br> Aperture: f/6.3<br> Filter Size: 95mm Front, 34mm Rear<br> Max Diameter: 3.9" (98mm)<br> Length: 4.7"<br> Weight: 1.55 lb (705g)<br><br> Included Items<br> Opteka 500mm f/6.3 Telephoto Lens<br> Opteka 2x Tele-Converter<br> Opteka T-Mount Lens Adapter<br> Opteka Padded Pouch<br> Opteka Lens Caps<br> Opktea 10 Year Warranty<br><br>.