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Telescopes

Learn about the different types of telescopes and microscopes, their magnification capabilities, and common aberrations. Discover how lenses and mirrors are used in telescopes, and how compound microscopes differ from telescopes. Understand aberrations like spherical aberration, distortion, and chromatic aberration.

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Telescopes

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  1. Telescopes

  2. Telescopes Refracting Telescope:2 lenses at opposite ends of a long tube. The objective lens is closest to the object, & the eyepiece is closest to the eye. See figure    The Magnification is

  3. Astronomical telescopes need to gather as much light as possible, which means that the objective must be as large as possible. So, usually, mirrors are used instead of lenses, because they can be made much larger & with more precision.

  4. A terrestrial telescope, used for viewing objects on Earth, should produce an upright image. Here are two models, a Galilean type and a spyglass:

  5. Compound Microscope A Compound Microscopealso has an objective & an eyepiece; it is different from a telescope because the object is placed very close to the eyepiece. The Magnification is (Valid for fo , fe << ℓ)

  6. Microscope. A compound microscope consists of a 10X eyepiece & a 50X objective 17.0 cm apart. Calculate(a) The overall magnification. (b) The focal length of each lens. (c) The position of the object when the final image is in focus with the eye relaxed. Assume a normal eye, so N = 25 cm.

  7. Aberrations of Lenses and Mirrors Spherical Aberration:Rays far from the lens axis do not focus at the focal point. Solutions:Compound-lens systems; Use only the central part of the lens.

  8. Distortion:Caused by variation in magnification with distance from the lens. The figures show Barrel & Pincushion distortion:

  9. Chromatic Aberration:Light of different wavelengths has different indices of refraction so that it focuses at different points.

  10. Solution:Use a chromatic doublet, made of lenses of 2 different materials.

  11. Summary • Lens uses refraction to form real or virtual image. • Converging lens: rays converge at focal point. • Diverging lens: rays appear to diverge from focal point. • Power is given in Diopters (m-1):

  12. Thin lens equation: • Magnification:

  13. Camera focuses image on film or electronic sensor; lens can be moved and size of opening adjusted (f-stop). • Human eye also makes adjustments, by changing shape of lens and size of pupil. • Nearsighted eye is corrected by diverging lens. • Farsighted eye is corrected by converging lens.

  14. Magnification of simple magnifier: • Telescope: objective lens or mirror plus eyepiece lens. Magnification:

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