Designs of reflective off-axis system

A design method for unobstructed, off-axis, reflective optical system is proposed. Based onthe three-mirror anastigmat (TMA), when pupil and field of view are off-axis properly, obstructingbetween mirrors is avoided. In view of aperture stop on the primary or secondary mirror, the primaryaberration formula is deducted respectively. According to the image character of TMA, afocal opticalconditions are acquired further. Unobstructed spatial observing telescope with excellent performance isdesigned with the help of Zemax, which have an entrance pupil diameter of 320mm, FOV of (±0.3°)×(±0.6°)and effective focal length of 1800mm.