Astronomy quiz question: reflector versus refractor costs

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

Large optical telescopes are reflectors rather than refractors because mirrors:
(A) are much easier to clean than lenses.
(B) are unaffected by light pollution, compared to lenses.
(C) can be used with different eyepieces, unlike lenses.
(D) can be made of lower quality materials than those used for lenses.

Correct answer: (D)

Since light must pass through a lens, the material must be internally flawless, in contrast to a reflector, where only the surface needs to be flawless.

Section 30676
Exam code: quiz03SL3w
(A) : 2 students
(B) : 14 students
(C) : 7 students
(D) : 16 students

Success level: 43% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.60