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 magnification
D) to increase the focal length
E) to combat chromatic aberration

Question

Quizplus · Accepted Answer

A reflecting telescope uses a concave mirror as the primary mirror to collect and focus light. However, the focal length of this mirror is limited by its size, making the telescope quite long. Adding a secondary mirror near the front of the tube allows the light to be redirected to the eyepiece, allowing the telescope to be shorter and more manageable.

Why Do Reflecting Telescopes Usually Have a Secondary Mirror in Addition