This mirror system is one of the oldest designs along with the Newton and the Gregory. There is usually from a paraboloid primary mirror and a hyperbolic secondary mirror. The light exit is at the rear end of the tube.
VISAC (Vixen 6th order aspherical catadioptric) incorporates high-precision 6th order aspherical primary mirror plus 3-element field correction lens, a ring-fixing metal on the objective primary mirror which decreases the lens flare.