Bower 500mm f/8.0 Manual Focus Telephoto Lens for Canon EOS

When combined with the T-mount, this mirror lens mounts to any Canon EOS camera and works on both "full frame" cameras like the 5D as well as the "APS-C" style digital SLR cameras.  However, the fixed f/8 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.

Despite this lens' long 500mm focal length, it has a compact 3 x 3.5" size and weighs under 1 pound, making it a bit easier to handle than normal 500mm refractor lenses (it should be used with a tripod or monopod in any case).  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).