Refracting telescope how it works

 Telescope

1) A telescope is an optical device which is used to observe distant objects.

2) There are two types of telescope

a) Refracting telescope.

b) Reflecting telescope.

 

 

 a) Refracting telescope how it works.

1) In refracting telescope, there are two lenses, one objective lens and an another eye piece.

2) Objective lens has larger aperture than the eyepiece.

 

 

3) When lights from objects located at very larger distance enters into the objective lens light focuses on the focal plane of the objective lens and a real image is formed at focal plane.

4) This real image acts as objects for the eye piece lens and produces an inverted image for the observer.

5) The magnifying power of a refracting telescope is

where

β = is angle subtended by the final image on the observer

α = angle subtended by the object at the eye of the observer

 

6) Now from the diagram

f₀  is the focal length of the objective lens

 

f_e  is the focal length of the eye piece

 

7) Therefore the magnifying power is

 

 

Disadvantages of refractive telescope

 

1) To observe large distance objects such as stars, plants etc. we need large size objective lens.

Large size of lenses are difficult to manage and they have heavy weight.

2) Refractive lenses produces chromatic aberration.

3) Refracting lenses creates less brighter image.