The Bower 500mm f/6.3 Manual Focus Lens is a catadioptric mirror T-mount lens, delivered in this configuration with a T-mount for the Nikon F-mount cameras. This lens is precision manufactured in South Korea.
When combined with the T-mount, this mirror lens mounts to any Nikon F-mount camera and works on both FX "full frame" cameras as well as the "APS-C" style DX digital SLR cameras. However, 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 upon certain cameras.
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).