Celestron 8″ Rowe-Ackermann Schmidt Astrograph (RASA) Optical Tube Assembly

The Celestron 8″ Rowe-Ackermann Schmidt Astrograph (RASA) Optical Tube Assembly is a dedicated imaging system engineered for astrophotographers who prioritise speed, wide-field coverage, and maximum light throughput. Unlike conventional Schmidt-Cassegrain telescopes, the RASA is designed exclusively for imaging, with the camera positioned at the front of the optical tube, enabling an exceptionally fast f/2.0 optical system.

At its core is a 203mm (8-inch) aperture optical system with a 400mm focal length, producing an ultra-fast focal ratio of f/2.0. This configuration allows the telescope to gather a large amount of light in a very short time, making it particularly effective for capturing faint nebulae, large galaxies, and expansive star fields. Compared to slower optical systems, the RASA 8 can significantly reduce exposure times while maintaining high signal-to-noise performance.

The optical design combines a Schmidt corrector plate, a spherical primary mirror, and a multi-element corrector lens assembly positioned near the focal plane. This Rowe-Ackermann design corrects for spherical aberration, coma, and field curvature, delivering a flat, well-corrected imaging field suitable for modern large-format CMOS sensors.

Celestron’s StarBright XLT coatings are applied to all optical surfaces to maximise light transmission and contrast. The system is optimised for imaging sensors with a large usable field and is widely used for fast survey-style astrophotography and deep-sky wide-field imaging projects.

The optical tube includes an integrated filter drawer system that accepts both 1.25″ and 2″ astronomical filters. A removable clear optical window is supplied as standard and can be replaced with narrowband or broadband filters without disturbing the optical train. This allows efficient filter changes while maintaining the telescope’s fast optical performance.

Thermal management is handled by an integrated 12V MagLev cooling fan mounted at the rear of the optical tube. This active airflow system helps the primary mirror reach thermal equilibrium more quickly, improving image stability and reducing thermal distortion during imaging sessions.

The 8″ RASA is built on a compact aluminium optical tube assembly designed for equatorial mounting. A CGE-style dovetail bar ensures compatibility with a wide range of medium to heavy-duty astrophotography mounts. Due to the front-mounted camera configuration, the system is intended exclusively for imaging use and is not suitable for visual observation.

The Celestron 8″ RASA OTA is designed for astrophotographers who want maximum imaging speed without sacrificing aperture. Its combination of f/2.0 optics, large 203mm aperture, and corrected wide-field imaging performance makes it a powerful instrument for fast, deep-sky astrophotography.