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Binoculars

Binoculars. TELESCOPES. Palomar 200-in. The Electromagnetic Spectrum. The Electromagnetic Spectrum. 0.0005 mm or 1/50000 in. 8.4-m Mirror Blank for Large Binocular Telescope. Polishing one LBT 8.4-m mirror. Functions of Telescopes. Collect more light --- depends on (diam) 2

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Binoculars

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  1. Binoculars

  2. TELESCOPES Palomar 200-in

  3. The Electromagnetic Spectrum

  4. The Electromagnetic Spectrum 0.0005 mm or 1/50000 in

  5. 8.4-m Mirror Blank for Large Binocular Telescope

  6. Polishing one LBT 8.4-m mirror

  7. Functions of Telescopes • Collect more light --- depends on (diam)2 • Resolve sources better (see more detail) • Magnify images (make larger)

  8. Telescope “Objectives”: Specially Shaped Main Optical Element Purpose: form an accurate representation of original scene at a “focus” Lens ---> “refracting” telescope Mirror ---> “reflecting” telescope

  9. Refraction: Bending of Light Rays at a Glass/Air Interface

  10. Prism Refraction Animation

  11. Reflection from a Smooth Surface

  12. Refracting Telescope Minimum 2 lenses needed for visual use Place detector here

  13. Image formation (Java demo)

  14. Image Inversion in Simple Telescope

  15. McCormick 26-in Refractor (1885)

  16. McCormick 26-in Lens (Doublet)

  17. Reflecting Telescopes

  18. Isaac Newton -- Co-inventor of reflecting telescope

  19. Modern Amateur Reflecting Telescopes

  20. “Catadioptric” (Lens+Mirror) Design(= CPC 800)

  21. Telescope Performance Characteristics • Focal Ratio (f/ number) • Magnification ("power") • Field of view • Light Gathering Power • Resolution

  22. Focal Ratio (or f/number) • f/ number = Obj FL / Obj Diam • Smaller numbers give more concentrated light in focal plane (better for faint extended objects); allow shorter exposures with film/electronic detectors • Higher numbers have better image quality; better for high magnification (e.g. for planets)

  23. Magnification • Defined to be ratio of apparent angular size of image to original angular size (without telescope) • Mag = FL (telescope) / FL (eyepiece) • For Celestrons, Mag = 2034 mm/FLE (mm) • Moderate magnifications (<150) best

  24. Field of View • FOV = True angular diameter -- i.e. as viewed without telescope -- of field visible in eyepiece. • Usually quoted in degrees or minutes of arc • Depends on eyepiece used • Is smaller for higher magnification with given telescope

  25. Light Gathering Power • Most important attribute of telescope • Light collected is proportional to the area of the objective, or to Dobj2 • If the pupil diameter of your eye is 5mm, an 8" telescope collects (203/5)2 = 1600x more light

  26. AGAIN, JONES' SNEAKY COLLEAGUES AIMED THE TELESCOPE AT THE SUN

  27. Table by D. Haworth

  28. Table by D. Haworth

  29. Image Quality (Resolution) • Design: configure optics to reduce inherent "aberrations" -- e.g. chromatic, spherical, etc. • Manufacture: figure optics to intended shape: must be better than “1/4 wavelength” • Physics: “diffraction” of light waves is reduced in larger telescopes • Atmosphere: turbulence in air strongly affects image blur. “Seeing” = size of blur. (Extrinsic)

  30. Chromatic Aberration (present in any refracting element)

  31. "Spherical Aberration" from Spherical Mirror

  32. Parabolic Mirror: perfect paraxial focus

  33. Parabolic Mirror: "coma" aberration off-axis

  34. Longer focal lengths reduce chromatic & spherical aberration (Hevelius, ca. 1650)

  35. “Schmidt-Cassegrain” design uses a thin refractive corrector to eliminate spherical aberration from a spherically-shaped primary

  36. Image Quality (Resolution) • Design: configure optics to reduce inherent "aberrations" -- e.g. chromatic, spherical, etc. • Manufacture: figure optics to intended shape: must be better than “1/4 wavelength” • Physics: “diffraction” of light waves is reduced in larger telescopes • Atmosphere: turbulence in air strongly affects image blur. “Seeing” = size of blur. (Extrinsic)

  37. “Diffraction” of Light Waves Ideal case Real waves

  38. Wave Tank Simulation

  39. 6" 20" Effects of diffraction on size of image of a double star in a telescope 200" 94"

  40. “Seeing” Caused by Atmospheric Turbulence

  41. Video of enlarged image of bright star in a large telescope. Image size/motion caused by Earth’s atmosphere.

  42. Seeing Effects • Seeing Videos (P. van de Haar)

  43. Telescope Designs: A Multitude • Optical design • Mounting design • Equatorial • Altitude-Azimuth

  44. Royal Greenwich Observatory, ca. 1640

  45. ReflectingTelescope Designs

  46. “Catadioptric” (Lens+Mirror) Design= Celestron CPC 800 Finder scope Eyepiece Secondary Baffle Diagonal Primary "Corrector Plate"

  47. ALL Large Telescopes areREFLECTORS • Why?

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