Q&A
  • Why is the image better at the center of the field?
  • Add on Sept. 28, 2011, 1:24 a.m.

All commercial eyepieces are made with spherical elements, as these are the only type that are easily mass produced. These naturally produce aberrations, which become much worse in highly convergent light beams. There is no way to avoid all aberrations when using spherical elements. Clever eyepiece designer can, however, minimize the objectionable ones and cause others to manifest themselves in an acceptable form.