Centon's budget mirror lens — the 500mm f/8 reflex for T2-adapted extreme telephoto on a budget.
The Centon 500mm f/8 Mirror Lens is a catadioptric (mirror) telephoto lens attached via a T2-to-Nikon adapter, a standardised 42mm thread mount that allows mirror and independent lenses to be fitted to various camera bodies with appropriate T-mount rings. Centon was a budget British camera accessories brand.
The lens uses a catadioptric (mirror) optical design — light reflects off two mirrors within the barrel, folding the optical path to achieve 500mm focal length in a compact barrel. The fixed f/8 aperture is inherent to the catadioptric design; no aperture ring is provided. The T2 mount couples it to Nikon F via an adapter.
Mirror lenses are distinctive for their donut-shaped out-of-focus highlights — a characteristic visual signature caused by the central obscuration of the rear mirror. They are substantially more compact than conventional 500mm lenses at f/8. The fixed f/8 aperture requires bright conditions or high ISO, and autofocus is not available. Budget brands like Centon typically show lower optical quality than major manufacturers.
Test at f/8 for sharpness and note that mirror lenses cannot be stopped down — f/8 is the only available aperture. Check the T2-to-Nikon adapter for secure coupling. Inspect the front and rear mirrors for dust, fungal spotting, or coating damage. Verify infinity focus accuracy. The donut bokeh is characteristic and not a defect.