Why do reflecting telescopes usually have a secondary mirror in addition to a primary mirror?
A) To increase the light gathering power
B) To make the telescope shorter
C) To increase the focal length
D) To combat chromatic aberration

Question

Quizplus · Accepted Answer

A secondary mirror is added in reflecting telescopes to make the telescope shorter. This is because reflecting telescopes use mirrors instead of lenses, and the focal length is determined by the distance between the primary mirror and the secondary mirror. Adding a secondary mirror allows for a shorter telescope without sacrificing focal length.

Why Do Reflecting Telescopes Usually Have a Secondary Mirror in Addition