How Is Spherical Aberration Usually Overcome in the Objective Lens

question 393

Multiple Choice

How is spherical aberration usually overcome in the objective lens of a refracting astronomical telescope?

• A) by making the lens very thin, with a long focal length
• B) by coating the lenses with an antireflective coating
• C) by grinding the lens surfaces to a parabolic shape
• D) by using a filter that allows only a small range of wavelengths (colors) through the telescope

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