A small refracting "spyglass" telescope has an objective lens with a focal length of about 30 inches. The world's largest refracting telescope at Yerkes Observatory has an objective lens with a focal length of 63.5 feet. If they both use the same eyepiece, how much larger is the image with Yerkes than with the spyglass?
A) about twice
B) about 16 times
C) about 25 times
D) about 625 times

Question

Quizplus · Accepted Answer

The magnification of a telescope is directly proportional to the focal length of the objective lens. The Yerkes telescope's focal length is 63.5 feet (or 762 inches), and the spyglass's focal length is 30 inches. Dividing 762 by 30 gives 25.4, which means the image with Yerkes is about 25 times larger than with the spyglass.

A Small Refracting "Spyglass" Telescope Has an Objective Lens with a Focal