Telescope
Telescope
Telescope
Topics
Pg.No
1.Spherical lenses 2
3.Lens formula 7
4.Astronomical Telescope 10
5.Parts Required 10
7.Uses 14
8.Future Aspects 15
9.Bibliography 16
1
Spherical lenses
Pole
The centre of the spherical refracting surface of the lens is called the pole. It is
the point where the principal axis meets the surface of the lens.
Optical Centre
The point on the principal axis at the centre of the lens is called the optical
centre.
Centre of Curvature
A lens has two spherical surfaces; these two spherical surfaces form a part of a
sphere. The centre of these spheres is known as the centre of curvature.
2
Principal Axis
The principal axis is an imaginary line passing through the centres of curvature
and the pole.
Aperture
The area of the lens suitable for refraction is called aperture. The aperture of the
lens is the effective diameter of its light-transmitting area.
Focus
Focus is the point onto which collimated light parallel to the axis is focused.
Focal Length
The focal length is the distance between the optical centre and the focal point or
focus of the lens
3
IMAGE FORMATION BY
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5
LENS FORMULA
6
LENS FORMULA
Lens formula relates the distance of object from the lens with
distance of image from the lens. Before deriving lens formula,
following sign conventions and assumptions must be kept in mind.
Assumptions
(1) Sizes of object and image are small
7
Deriving the Lens Formula
Lens formula can be derived for any one of the cases of image
formation shown before. When we derive a formula, we keep in
mind the sign conventions and substitute each value with sign. This
makes a formula suitable to be applied in any case. Here, we shall
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Real Object and Real image (Convex lenses)
CA = -u (object distance)
triangleA’AC – triangleB’BC
AA'/B'B=CA/CB ………(i)
CA/CB=CF₂/(CB-CF₂)
=>-u/+v=f/v-f
uv-uf=-vf
uv=uf-vf
9
TELESCOPE
AstronomicalTelescope
Parts Required
10
• Eyepiece: This lens is fitted at the back side of the
telescope. It should have a smaller aperture (diameter) and
focal length as compared to the objective lens.
11
an enlarged, virtual image of I. Objects that are viewed with a
telescope are usually so far away from the instrument that the
first image I is formed very nearly at the second focal point of the
objective lens. If the final image I’ formed by the eyepiece is at
infinity (for most comfortable viewing by a normal eye), the first
image must also be at the first focal point of the eyepiece. The
distance between objective and eyepiece, which is the length of
the telescope, is therefore the sum of the focal lengths of
objective and eyepiece,
ƒ1 +ƒ2.
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And the angular magnification M is
13
Uses
14
Modified Models & Designs
Galileo’s Telescope
Keplerian Telescope
Achromatic Refractor
Apochromatic Refractor
Image of a refracting
fromCincinnati in
15
Bibliography
• HTTPS://GOOGLE.COM
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