Foci and Mirrors

This week’s discussion topic will attempt to answer the question:

Suppose your Newtonian reflector has a mirror with a diameter of 20 cm and a focal length of 2 m. What magnification do you get with eyepieces whose focal lengths are: a. 9 mm, b. 20 mm, and c. 55 mm?

From my textbook:

The magnification of a reflecting telescope is equal to the focal length of the primary mirror divided by the focal length of the eyepiece lens:

Magnification = Focal Length of Primary / Focal Length of Eyepiece

In the question stated above, the three different eyepieces will result in the following magnifications:

2000 mm / 9 mm = 222X
2000 mm / 20 mm = 100X
2000 mm / 55 mm = 36X

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