mam, What is the monochromatic abberation in reflecting telescope?
There are five monochromatic aberrations:
Spherical aberration is an axial aberration, one that affects the entire field equally, including the center of the field. The other four aberrations are off-axis aberrations, affecting the star images increasingly toward the edge of the field but not at the center. astigmatism is the problem of focussing horizontal and vertical axis simultaneously.