Choose the one alternative that best completes the statement or answers the question.
-Cal is viewing the Moon with his new telescope, using a 10-mm focal length eyepiece. For greater detail, he wishes to double the magnification of his telescope. An eyepiece having which one of the
Following characteristics will accomplish this for him?
A) 12 mm
B) 8 mm
C) 200 diopters
D) 5 diopters
E) 40 diopters