This download is a PowerPoint and lesson plan explaining how reflecting telescopes work to produce an image. Also discussed are spherical aberrations.
This is lesson 2 / 12 from my Astrophysics / Cosmology course, all available individually or as a bundle at a reduced price.
Cassegrain arrangement using a parabolic concave primary mirror and convex secondary mirror.
Ray diagram to show path of rays through the telescope up to the eyepiece.
Relative merits of reflectors and refractors including a qualitative treatment of spherical and chromatic aberration.