Basic Astronomical Telescope
Basic Astronomical Telescope
Basic Astronomical Telescope
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.
Principal Axis
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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
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IMAGE FORMATION BY
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LENS FORMULA
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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
(4) Distances measured above principal axis are positive and below
principal axis are negative.
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Deriving the Lens Formula
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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
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TELESCOPE
Astronomical Telescope
Parts Required
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• 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.
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The objective lens forms a real, reduced image I of the
object. This image is the object for the eyepiece lens, which forms
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
Uses
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1. Astronomical telescopes are being used worldwide for
scientific as well as educational purposes.
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Modified Models & Designs
Galileo’s Telescope
Keplerian Telescope
Achromatic Refractor
Apochromatic Refractor
Image of a refracting
fromCincinnati in
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Bibliography
• HTTPS://GOOGLE.COM
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