Astronomy quiz question: Celestron NexStar® primary focal length

Astronomy 210 Quiz 3, fall semester 2012
Cuesta College, San Luis Obispo, CA

The primary focal length for the Celestron NexStar® Maksutov-Cassegrain focus reflector shown at right is approximately:
(A) the width of the tube.
(B) the length of the tube.
(C) twice the length of the tube.
(D) three times the length of the tube.

Correct answer (highlight to unhide): (C)

Light enters the tube and is then reflected off of the primary mirror at the back, coming to a focus as it travels back up the tube, then deflected by the secondary mirror at the front of the tube, then going back down the tube to come to a focus (after reflecting off of another secondary mirror); thus traveling twice along the length of the tube while coming to a focus.

Section 70160
Exam code: quiz03ni3R
(A) : 1 student
(B) : 2 students
(C) : 23 students
(D) : 3 students

Success level: 81% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.22

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