The Bower 800mm f/8 Manual Focus Lens is a catadioptric mirror T-mount lens, precision manufactured in South Korea.
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 or for nearly any film camera. However, in every case the fixed f/8.0 aperture is not communicated to the camera body. As such, you can use the camera in the "M" manual exposure mode or the "A" aperture-priority mode (if your camera is so equipped).
This lens, at 4.4 x 5.2" and just over 2 pounds, has a broad diameter and stocky build. It is a bit easier to handle than a normal 800mm refractor lens, but it is still a super-telephoto in any case (you should use a tripod/monopod in any case for best results). 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.
This lens is an ideal candidate for astrophotography use when mounted to a Vixen GP2 Photo Guider (or other motorized equatorial telescope mount).