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| Astronomical Telescope |
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| This type of telescope is used to view heavenly bodies like stars, planets and satellites. |
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| Astronomical Telescope |
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| It consists of two convex lenses called objective and eyepiece. The objective is of large focal length whereas the eyepiece is of short focal length. The distance between the two lenses can be adjusted by adjusting the tube which holds the lens. |
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| The ray diagram showing the principle of the astronomical telescope is given below. |
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| Astronomical Telescope |
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| The rays of light coming from a distant object (PQ) form a parallel beam of light. This parallel beam of light is focused by the objective in a plane passing through its focus and perpendicular to the axis and forms the image (PlQl). This plane is known as focal plane. The eyepiece is adjusted so that the image PlQl lies in its focal plane. The light beam after striking the eye lens emerges parallel and final image PllQll is formed at infinity. This adjustment of the telescope is known as normal adjustment. |
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| Magnifying power of an astronomical telescope may be defined as the ratio of the angle subtended at the eye by the image to the angle subtended at the eye by the object. |
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| From the ray diagram we know that: |
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| PlC is the focal length of the objective and |
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| PlD is the focal length of the eye piece. |
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