Question

Draw a ray diagram of a reflecting telescope (Cassegrain) and explain the formation of the image. State two important advantages that a reflecting telescope has over a refracting telescope.

Hint:

In reflecting telescopes, mirrors are used instead of lenses. This helps avoid chromatic aberration and allows for larger apertures.

Answer 1

Reflecting Telescope - Cassegrain Type

A reflecting telescope uses mirrors to gather and focus light. The Cassegrain type has two mirrors: a primary concave mirror and a secondary convex mirror.

The primary mirror collects light from distant objects, and the secondary mirror reflects the light to an eyepiece located at the focal point of the primary mirror.

Diagram Explanation:

• The rays from a distant object are reflected by the concave primary mirror.
• The reflected rays converge at the focus of the primary mirror.
• The secondary convex mirror reflects these rays towards the eyepiece.
• The eyepiece focuses the rays into a clear image.

Advantages of Reflecting Telescopes:

1. No Chromatic Aberration: Reflecting telescopes use mirrors instead of lenses, so they don’t suffer from chromatic aberration, which causes color distortion in refracting telescopes.
2. Larger Apertures: Reflecting telescopes can have much larger apertures than refracting telescopes, allowing them to collect more light and observe fainter objects.