Question

In a reflecting telescope, a secondary mirror is used to:

• A. Reduce the problem of mechanical support
• B. Remove spherical aberration
• C. Make chromatic aberration zero
• D. Move the eyepiece outside the telescopic tube

Hint:

In reflecting telescopes, the secondary mirror is used to: - Redirect light to a more accessible viewing position. - Enable a compact design (Cassegrain configuration). - Prevent obstruction by placing the eyepiece outside the main tube.

Answer 1

The Correct Option is D

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: \[ \boxed{{Move the eyepiece outside the telescopic tube}} \]