Celestron C90 500mm f/5.6 Mirror Lens

The Celestron C90 is a 500mm f/5.6 catadioptric mirror lens designed primarily as a compact spotting scope and telescope, though its T-mount thread allows it to be adapted for use as a photographic lens on a range of camera systems via appropriate T-mount adapters. The catadioptric optical design uses a combination of mirrors and lens elements to fold the optical path, achieving a 500mm focal length in a notably compact and portable form factor compared to a conventional refractive telephoto lens of the same focal length. The fixed f/5.6 aperture is characteristic of catadioptric designs, and out-of-focus highlights render as distinctive donut-shaped rings rather than the circular discs produced by conventional lens designs. The compact Maksutov-Cassegrain optical formula delivers a long focal length in a short physical tube, making it a practical option for wildlife, nature, and astronomical observation as well as photographic use with appropriate adapters.

– 500mm focal length catadioptric mirror lens
– Fixed f/5.6 aperture
– Maksutov-Cassegrain optical formula for compact form factor
– Distinctive donut-shaped out-of-focus highlight rendering
– T-mount thread for camera adapter compatibility
– Usable as spotting scope, telescope, and photographic lens
– Compact and portable construction for its focal length
– Suitable for wildlife, nature, and astronomical observation