The Bower 800mm f/8 Manual Focus Lens is a catadioptric mirror T-mount lens, precision manufactured in South Korea. In this particular configuration, it is delivered with a T-mount to fit the Canon EOS system cameras.
This mirror lens works on both "full frame" cameras like the 5D or film cameras as well as the "APS-C" style digital SLR cameras. However, in all cases the fixed f/8.0 aperture is not communicated to the camera body. As such, you can only use the camera in the "M" manual exposure mode or the "A" aperture-priority mode.
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).