From the March 2009 issue

The early reflectors

Compare the optics of the first three telescope designs.
By | Published: March 23, 2009
The first reflecting telescopes — telescopes that use a mirror instead of lens to gather the incoming light — appeared in the 1660s and 1670s. Three reflecting telescope designs — Gregorian, Newtonian, and Cassegrain — landed on the scene within 10 years of each other.