2 Products
RASA Tubes
The RASA tube (Rowe-Ackermann Schmidt Astrograph) is a catadioptric optical system designed exclusively for deep-sky astrophotography: a fast optical design, typically f/2 or f/2.2, that concentrates light across wide fields with extreme sharpness from centre to edge. Unlike refractor astrographs or Newtonians, the RASA places the sensor directly at the front primary focus — eliminating secondary mirrors and additional optical paths — to maximise light transmission to the sensor.
RASA tubes dramatically reduce exposure times compared to f/8 or f/10 systems: at the same aperture, an f/2 collects approximately 16 times more light than an f/8, making it possible to photograph nebulae, galaxies and star clusters in minutes rather than hours. They are instruments built for imagers who want to maximise productivity in every session, paired with OSC or monochrome cooled cameras and precision goto mounts.
RASA or classic astrograph? Advantages, limitations and how to choose
The RASA is optimised for a single purpose: deep-sky imaging with the shortest possible exposure times. Its front primary focus architecture does however impose some operational constraints: the camera must be mounted at the front of the tube with its weight centred on the optical axis, and standard filters cannot be used conventionally — EOS clip-in filters or dedicated filter wheels positioned in front of the sensor are required. Visual observation is excluded by design.
Compared to a refractor astrograph (typically f/5–f/7), the RASA offers significantly higher optical speed and wider fields on APS-C and full-frame sensors, but requires more careful management of focus, collimation and the imaging chain. Compared to a fast Newtonian astrograph, the RASA eliminates edge coma without external correctors, thanks to the integrated Schmidt corrector plate.
When to choose a RASA tube:
- You want to photograph deep-sky objects with minimal exposure times
- You use cooled OSC or monochrome cameras on a goto mount
- You are targeting extended nebulae, galaxies and star clusters with wide fields
- You want an instrument dedicated exclusively to imaging, with no visual compromises
