Sigma's mirror telephoto for Yashica AF — the 600mm f/8 reflex at extreme reach.
The Sigma 600mm f/8 Mirror Lens for Yashica AF mount is a catadioptric super-telephoto providing 600mm reach in a compact mirror barrel. The fixed f/8 is inherent to the design. The Yashica AF mount (also known as Contax/Kyocera AF) is extremely limited. Mirror lenses fold the optical path for compact super-telephoto reach.
Mirror lens characteristics — doughnut-shaped bokeh, lower contrast, fixed f/8 aperture. The 600mm provides serious super-telephoto reach. Sharpness is acceptable in the centre. The compact barrel is the advantage of mirror design versus refractive alternatives. Manual focus. The Yashica AF mount severely limits camera compatibility.
Yashica AF mount — extremely limited proprietary system. No AF despite the mount name — mirror lenses are manual focus. Fixed f/8. Weight relatively light for 600mm — the mirror design advantage. Build quality functional Sigma. The Yashica AF mount limits all compatibility. Adapters essentially non-existent.
Essentially valueless in Yashica AF mount. The mount limits all use. Mirror lens with fixed f/8. Not recommended. The same mirror lens design exists in more useful mounts. Only for Yashica AF camera owners — an extremely small group.