1. Correcting Spherical Aberrations
(I) Aspheric lens
-Spherical lens do not have a well-defined focus:
- An aspheric lens or asphere is a lens whose surface profiles are not parts of a sphere (see below, right). The asphere's more complex surface profile changes the path of the light rays such that spherical aberration is reduced.

2. (II) Schmidt Corrector Plate
Spherical mirrors do not have a well-defined focus:
- One method to correct for such spherical aberration is to place a Schmidt corrector plate at the center of curvature of the mirror C.
- The Schmidt corrector plate is thicker in the middle and the edge. Some portions “converge “the light rays while others “diverge” the light rays. This corrects the light paths so light reflected from the outer part of the mirror and light reflected from the inner portion of the mirror is brought to the same common focus F (see figure below).