The Vivitar 500mm f/8 mirror lens was a catadioptric super-telephoto sold from the late 1970s through the 1980s, offering compact, affordable long reach for manual-focus SLR owners who could not justify the size or cost of a conventional refractive 500mm lens.
It is a manual-focus mirror (catadioptric) lens with a fixed f/8 aperture and a close-focusing helicoid, built on a T-mount rear interface accepting screw-in T2 adapters for fitting to different camera systems. Weight, filter thread and minimum focus distance are not confirmed from available sources.
Its catadioptric design produces the doughnut-shaped out-of-focus highlights characteristic of mirror lenses, and the fixed aperture removes exposure control from the lens itself, trading conventional light control for compactness at 500mm.
It remains a low-cost way to try super-telephoto framing on the secondhand market. Check the mirror elements for haze or delamination, confirm a T2 adapter for the intended mount is included or available, and inspect the focus helicoid for smooth, unworn travel.