Question

Draw a ray diagram of reflecting telescope. Explain its working.

Hint:

The key feature of a reflecting telescope is the use of a concave mirror as the objective to collect and focus light. The different types (Newtonian, Cassegrain, etc.) mainly differ in how the light is redirected by the secondary mirror to the eyepiece.

Answer 1

Step 1: Understanding the Concept: 
A reflecting telescope is an optical instrument used to view distant objects. Unlike a refracting telescope which uses lenses, a reflecting telescope uses a large concave mirror as its primary light-gathering element (the objective). This design avoids chromatic aberration and allows for the construction of very large diameter objectives. The Cassegrain design is a common type. 
Step 2: Ray Diagram (Cassegrain Telescope): 

Step 3: Working Principle: 
Objective Mirror: A large concave parabolic mirror serves as the objective. It collects parallel rays of light coming from a distant astronomical object (like a star or a planet). 
Formation of Intermediate Image: The objective mirror reflects these parallel rays, causing them to converge towards its principal focus. 
Secondary Mirror: Before the rays can converge to form an image, they are intercepted by a smaller, convex secondary mirror. This secondary mirror is positioned coaxially with the primary mirror. 
Redirection of Light: The secondary mirror reflects the light rays back through a hole in the center of the primary objective mirror. 
Eyepiece and Final Image: The rays then pass through an eyepiece (a convex lens or a system of lenses) located behind the primary mirror. The eyepiece acts as a magnifier, producing a final, highly magnified virtual image, which is then viewed by the observer. 
Advantages: Reflecting telescopes are free from chromatic aberration (color distortion) because mirrors reflect all wavelengths of light in the same way. They can also be built with much larger apertures than refracting telescopes, giving them greater light-gathering power and better resolution.