Your friend, a graduate student in astronomy, is giving you a special tour of the local observatory. You notice that you are viewing the image from the big telescope from underneath the primary mirror; the beam of light has come through a small hole in the main mirror to an eyepiece below. This telescope uses what focusing arrangement?
A) prime focus
B) Newtonian focus
C) Cassegrain focus
D) Galilean focus
E) out of focus

Question

Quizplus · Accepted Answer

The Cassegrain focus uses a primary mirror to gather light and a secondary mirror to reflect it back through a hole in the primary mirror to an eyepiece or detector below. This arrangement allows for a longer focal length and sharper images compared to a prime focus arrangement where the eyepiece is located at the bottom of the telescope. The Newtonian focus uses a tilted flat secondary mirror to reflect the light out of the side of the telescope tube. The Galilean focus is a type of optical design used in binoculars and telescopes that use lenses rather than mirrors. Out of focus is not a valid option for a telescope's focusing arrangement.

Your Friend, a Graduate Student in Astronomy, Is Giving You