9.4 Astronomical telescope (Refracting type)

1.1 Refractive index of light
1.2 Types of medium

2.1 Refraction from a spherical surface

3.1 Shift due to a glass slab
3.2 Lateral Magnification

4.1 Sign convention
4.2 Some important terms
4.3 Ray tracing
4.4 Image formed by covex lens
4.5 Image formed by concave lens

5.1 Thin Lens Formula
5.2 Magnification and Power of lens
5.3 Combination of lenses
5.4 Displacement method to find focal length.
5.5 Silvering of lens

6.1 Critical angle
6.2 Application of total internal reflection

7.1 Dispersive power

8.1 Rainbow

9.1 Spectrometer
9.2 Simple microscope
9.3 Compound microscope
9.4 Astronomical telescope (Refracting type)
9.5 Terrestrial telescope
9.6 Galileo's terrestrial telescope
9.7 Reflecting type telescope

It consists of two converging lens. The one facing the object is known as objective or field lens and has large focal length and aperture while the other facing the eye is known as eye-piece or ocular has small focal length and aperture.

When the final image is formed at infinity (normal adjustment), $$M = \frac{{{f_o}}}{{{f_e}}}$$

Length of tube, $L = {f_o} + {f_e}$

When the final image is formed at least distance of distinct vision, $$M = \frac{{{f_o}}}{{{f_e}}}\left( {1 + \frac{{{f_e}}}{D}} \right)$$

Length of tube, $L = {f_o} + \frac{{{f_e}\,D}}{{{f_e} + D}}$