In a reflecting telescope, a secondary mirror is used to:
Show Hint
- Reduce the problem of mechanical support
- Remove spherical aberration
- Make chromatic aberration zero
- Move the eyepiece outside the telescopic tube
The Correct Option is D
Solution and Explanation
Step 1: Understanding the purpose of a secondary mirror. - A reflecting telescope primarily uses a concave primary mirror to collect and focus light. - A secondary mirror is placed at an intermediate point to redirect the focused light to an eyepiece.
Step 2: Function of the secondary mirror. - The primary mirror focuses light inside the telescope tube, making it difficult to place an eyepiece directly. - The secondary mirror redirects the light outside the tube, allowing for convenient viewing. - This design is seen in the Cassegrain and Newtonian telescopes.
Step 3: Evaluating other Option. - (A) Reducing mechanical support problems → Incorrect. The secondary mirror is not primarily used for structural support. - (B) Removing spherical aberration → Incorrect. Spherical aberration is corrected by parabolic mirrors, not by the secondary mirror. - (C) Making chromatic aberration zero → Incorrect. Chromatic aberration is caused by lenses, but reflecting telescopes use mirrors, which naturally eliminate this issue.
Final Answer: \[ \boxed{{Move the eyepiece outside the telescopic tube}} \]
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