Telescope is an optical instrument used for viewing distance objects, planets and interstellar objects. It consists of two or more convex lens or mirrors, one called as object lens and other as eye lens which is also called as eye piece and lies close to eye aperture.
Principle of Construction of Telescope
Older telescope were constructed with simple techniques. The advancement in construction methods are getting more advanced and commercialized. The main principal of construction in all types of telescope are:
The two conversing lens are arrange in a tube. One is larger than other.
Large convex lens is adjusted to end of tube for receiving light from distance object.
Other small lens is adjusted near the eye aperture.
Both lens is adjusted in such a way that first image formed by large lens falls within the focal length of the small lens.
Eye aperture is located in such a way that it can receive final image made by small convex lens.
Working Principle of Telescope
The theoretical explanation of working of telescope is simple but quite complex. The objective lens collect light rays from source and converse them into single point forming real, inverted, and point size image. This image lies in the focal length of eye lens. The eye lens again pass the intermediate image rays for forming final clear image.
The final image formed is virtual, inverted and magnified. This final image formed is only seen when look through telescope.
Types of Telescope
There are different types of telescope used in different fields. All of them have similar construction mechanism and working process with more or less modification for adjusting to work in for which it is made. They are:
Astronomical Telescope
It is used to observe celestial bodies like stars, planets, moon etc. It is quite larger and its objective lens is large to collect more rays from the source. It also forms two image, one intermediate and other final image. Final image is visible to eye.
Terrestrial Telescope
It is a land telescope used to observe distant object on earth. In between objective and eye lens there is erecting convex lens of focal length f. The image formed is virtual, erect and magnified.
Galilean Telescope
It was constructed by Italian scientist Galileo Galilei and named after him. It is a kind of refracting telescope. It also consists of two lens. But objective is convex lens with large focal length whereas eye piece (lens) used is concave lens. The final image formed is virtual, erect or upright and magnified formed at infinity.
Galileo used this simple construction to view outer surface of moon, Jupiter and Venus.
Some Quick Facts
- Binoculars and zoom lenses are based on refracting telescope principle.
- An endoscope used for examining digestive tract is narrow telescope.
- Telescope does not increase size of object but it forms image nearer.
- A telescope which uses lens are called refracting telescope.
- A telescope which uses mirror are called reflecting telescope.
- Telescope with mirror is better than telescope build with lens.
- Larger and advanced telescope uses mirror as lens because it is lighter, easily producible, great nature of concentrating light rays etc.
