RASA stands for Rowe Ackermann Schmidt Astrograph: Dave Rowe and Mark Ackermann are renowned optical instruments developers.
These telescopes have been specially developed for astrophotography. RASA astrographs have a very fast aperture ratio of f/2. You capture images twenty times faster than with an SC optic with f/10! This eliminates the need for tracking control (guiding). Even with an altazimuth mount, deep sky images are possible!
The optics have a four-lens corrector with rare earth glass that suppress colour and image defects.
A very important factor in evaluating the performance of telescopes is transmission, that is the proportion of incident light that arrives at the image plane.
The main characteristics of the StarBright®-XLT coating are as follows:
The entire optical system consisting the corrector plate, mirror and lenses achieve a transmission maximum of 89% at 520 nanometres (where the dark-adjusted human eye has its highest light sensitivity). The average transmission over the entire visual spectrum from 400 to 750 nanometres is 83.5%.