A 500mm f/8 mirror telephoto lens with a T2 mount.
The Centon 500mm f/8 Mirror Lens is a catadioptric (mirror/lens) telephoto using a Cassegrain-type reflector design that produces a very compact physical size for a 500mm focal length. The fixed f/8 aperture (no iris blades) is a characteristic of all mirror lenses. T2 mount requires a system-specific T2 adapter.
500mm focal length, f/8 fixed aperture (no iris — mirror lens), T2 thread mount (requires camera-specific T2 adapter), compact physical size, characteristic donut-shaped bokeh.
Mirror lenses produce distinctive donut-shaped out-of-focus highlights (the secondary mirror shadow creates a ring-shaped blur circle). The fixed f/8 aperture means exposure is controlled only by shutter speed and ISO. No depth-of-field control via aperture. The compact physical size for 500mm is the primary advantage over conventional telephoto designs.
Note the fixed f/8 aperture — no aperture ring is present, which is normal for mirror lenses. Confirm T2 adapter compatibility with your camera system. Inspect optics for haze or contamination — mirror lenses are susceptible to internal dust. Test for correct infinity focus registration.