The Askar F3.9 full-frame reducer is designed for both FRA400 and FRA500 astrographs. The 0.7x reduction factor produces a 280mm focal length on FRA400 (350mm on FRA500) at f/3.9, dramatically shortening exposure times for deep-sky imaging. Standard 55mm back focus with built-in M48×0.75 2" filter thread.
