The Bower 500mm f/6.3 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. 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.
This lens is an ideal candidate for astrophotography use when mounted to a Vixen GP2 Photo Guider (or other motorized equatorial telescope mount).