Question

What is an astronomical telescope? Draw ray diagram for an astronomical telescope when final image is formed at infinity.

Hint:

In an astronomical telescope, the distance between the objective and the eyepiece is the sum of their focal lengths. To form an image at infinity, the intermediate image should be at the focal point of the eyepiece.

Answer 1

An astronomical telescope is a type of optical telescope used to observe distant celestial objects. It consists of two lenses: the objective lens and the eyepiece. 1. Objective Lens:
The objective lens gathers light from a distant object and forms an intermediate image at its focal plane. 2. Eyepiece Lens:
The eyepiece lens magnifies the intermediate image, making it visible to the eye. The final image is formed at infinity, meaning it is highly magnified and can be observed clearly without straining the eyes. 3. Ray Diagram:
In the case where the final image is formed at infinity, the object is placed at a distance greater than twice the focal length of the objective lens. The rays from the object are parallel and converge to form an image at the focal plane of the objective lens.
The eyepiece lens then produces an image that appears at infinity. The ray diagram for an astronomical telescope when the final image is at infinity is as follows:
- The objective lens produces a real, inverted image at the focal plane.
- The eyepiece lens magnifies this real image and makes it appear as an inverted image at infinity.