Great for the purpose it was created to do
A well-built classic mirror lens, that's compact and light in weight. The manual focus reaches in much closer than the majority of long focal length camera lenses, and is somewhat easy after you get the hang of it. IQ is somewhat better than an inexpensive conventional 400mm f/6.3 zoom lens, although not spectacular. The bokeh is huge doughnuts, which most often is a distraction when specular highlights occur in the unfocused areas. In short, The bottom line is that if you don't have a need for a compact 500mm lens, pass this lens up -- it's nice but also strange. If you do need a 500mm lens, then this lens is just about as good it gets and priced very modestly.
As the image above shows, the lens features a wide diameter and chunky build, allowing it to be a bit more uncomplicated to deal with than a regular refractor lens. In addition has a very different depiction of unfocused expanses than a regular lens; highlights turn out as doughnut-appearing rings with increased saturation and contrast at the rings edges than in the center.
The Manual Focus Catadioptric Mirror Bower 500mm f/6.3 Lens is a T-mount design which is manufactured with
precision in South Korea.
By combining the lens with with a T-mount designed to fit on your camera, this mirror lens attaches to camera and functions with both "full frame" along with "APS-C" style DSLR cameras. These T-Mounts are offered for every DSLR camera system, along with the C-mount system. Although, as in every situation the fixed length f/6.3 aperture cannot communicate with your camera. As such, you must shoot with the lens set to manual exposure mode (M) or aperture-priority (A) mode only.
Currently only Sony (formerly Minolta) offers a 500 mm catadioptric
lens for their Alpha range of cameras.
Samyang offers a variety of uniquely priced optics, delivering a lot of optical
capability for very little money. These rebranded catadioptric lenses are
available under the names of Bower, Opteka,
Phoenix, Rokinon, Sakar,
Vivitar and others.
Mirror lenses can produce pictures and under carefully chosen conditions they
may even produce pretty good ones. However, these situations are rare and therefore
most will have unsteady background blur. Most mirror lenses suffer from a rather mediocre optical performance. This may all be fine for personal purposes and for documentation but most likely you'll not be able to sell such pictures. Therefore a classic (refractive) lens like a 400/5.6 fix-focal or even a xx-500mm zoom
or even a 70-300-f/4-5.6 with a 1.4 or 2x teleconverter is usually a better and more serious approach. Nonetheless mirrors are quite cheap
(but you get what you pay for).
(To rephrase the paragraph above: Mirror Lenses are So Much Junk!)