Optics


   
 
Reflecting Telescope
Refraction Telescope
 
The objective lens is replaced by a concave parabolic mirror of large aperture. The images in such telescopes are brighter and have a high resolving power compared to astronomical telescope.
 
 
Cassegrainan Reflecting Telescope
 
where O-objective, B-convex mirror, E- eye piece
 
 
Newtonian Reflecting Telescope
 
 
Galilean Telescope
 
This consists of an objective lens O, a convex lens of large focal length and aperture and an eyepiece (E), a concave lens of a short focal length and small aperture separated by a distance equal to the difference in their focal lengths. The parallel beam passing through the objective would have converged at a distance f0 to form the image A1B1. But the eyepiece intercepts these rays and converts them into a parallel beam.
 
 
 
The magnifying power is given by
 
 
Telescope is given by
 
L = fo - fe
 
The advantages of this telescope is
 
The final image is erect
 
The length of the telescope is small
 
The disadvantages are:
 
The field of view is small
 
Cross wires cannot be used
 
 
     
   
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Optics