The document summarizes the history of telescopes from Galileo to Hubble. It discusses the goals and types of refracting telescopes using lenses, reflecting telescopes using mirrors, and catadioptric telescopes using both lenses and mirrors. It covers important figures like Galileo, Newton, and developments like resolving chromatic aberration and creating parabolic mirrors to reduce spherical aberration. Large modern telescopes are also highlighted, such as the Keck observatory's segmented mirrors.

1. Telescopes From Galileo to Hubble Scott A. Berg January 13, 2007 Pewaukee Astronomy Club Harken Observatory - Pewaukee Public Library http://pewaukeeastro.com/ Pewaukee Astronomy Club Harken Observatory

7. 8 mm or 50 mm 2 300 mm or 70,000 mm 2 A 12” diameter (300 mm) aperture, like the scope at the Harken Observatory, is about 1,400 times the area of the largest human pupil, so it gathers far more light. All that light comes out an eyepiece or into a camera. Pewaukee Astronomy Club Harken Observatory

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14. Reproductions Reproductions of the two surviving telescopes made by Galileo were made for Griffith Observatory & Adler Planetarium in 2006. They are museum quality and very elaborate. The same artisans often recreate historic instruments for the PBS show NOVA. http://www.scitechantiques.com/ Actual Scope Pewaukee Astronomy Club Harken Observatory

16. But how well did Galileo’s telescopes work? Pewaukee Astronomy Club Harken Observatory

17. Reproduction of Galileo’s Scope Celestron C8 Images are from a highly accurate reproduction of Galileo’s favorite scope. Tom Pope and Jim Mosher http://www.pacifier.com/~tpope/index.htm Pewaukee Astronomy Club Harken Observatory Reproduction of Galileo 23mm Mars Jupiter Saturn

18. Eyepiece Finder Primary or Objective Lens Counter Weight Pewaukee Astronomy Club Harken Observatory

19. ↑ ↑ Target (star) Objective Lens fits in Aperture of diameter A Eyepiece Lens Objective Lens Focal Length (F o ) Eyepiece Lens Focal Length (f e ) Magnification = F o /f e Focal ratio = F o /A The front “objective” lens brings light to a focal point in the “middle” of the tube. The light rays cross, inverting the image. The eyepiece picks up the rays and puts them back in a straight line. All the light coming in the objective is presented to your smaller diameter eye, so it’s brighter. The ratio of two lens focal lengths determines magnification. The eyepiece lens moves to allow focus. Focal Point Image All the light, less area, brighter Pewaukee Astronomy Club Harken Observatory

21. Lens (or prism) can Separate Color Pewaukee Astronomy Club Harken Observatory Blue focal point Red focal point Green focal point (the one used) Chromatic Dispersion is caused by different wavelengths of light (colors) being bent when moving from air to glass and becoming separated. Focus is a compromise between which color to believe is the focus. Since the human eye is most sensitive to green, it’s the one viewers choose.

22. Solution #1 Thinner lens -> Longer Focal Length -> Less Distortion ↑ ↑ ↑ ↑ Thinner Lens Longer Focal Length Pewaukee Astronomy Club Harken Observatory

23. Solution #1 Thinner lens -> Longer focal length -> Less distortion http://amazing-space.stsci.edu/ Pewaukee Astronomy Club Harken Observatory

24. “ Six to eight feet—that was the length of a good astronomical telescope in 1645. Five years later it was 10 to 15 feet. Ten years after that, 25 feet. Ten years after that, 40 to 50 feet. By 1673, [Polish astronomer] Johannes Hevelius had constructed a telescope 150 feet long on the shores of the Baltic Sea....One astronomer cheered the coming day when aerial telescopes would have a focus of 1,000 feet and human spectators could marvel at the antics of the animals on the Moon.” Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens, by Richard Panek Pewaukee Astronomy Club Harken Observatory

25. Johannes Hevelius Scope Built 1673 150 ft long Wooden trough “ The telescope would shake in the smallest breeze, the wooden planks warped, and the ropes had to be constantly adjusted because of stretching and shrinking in the humidity. The unsteadiness also made it difficult to line up the lenses for observations. Due to all these difficulties, this huge telescope was rarely used.” http://amazing-space.stsci.edu/ Pewaukee Astronomy Club Harken Observatory

26. Focal Ratio = Focal Length / Aperture f/12 + “Slow” Easier to get high magnification. More forgiving of optical imperfections than faster systems. Small field of view. Large depth of field – focus good for target and background (not as relevant for stars). f/7 to f/11 Medium. All Meade LX200 scopes (like Harken Observatory’s) have a focal length of f/10 (120”/12” or 3050mm/305mm). Common range for amateur scopes. f/3.5 to f/6 “Fast” Harder to get high magnification. Wide field. 1 ) The same eyepiece yields different magnification with different f-ratios. You can get the same magnification at different f/ with another eyepiece. 2 ) When using digital imaging, you must match focal length to pixel size. Pewaukee Astronomy Club Harken Observatory

27. Solution #2 Achromatic Lens A convex lens (white) of ordinary glass and a double-concave lens (yellow) of flint (leaded) glass bends the light twice, cancelling out the error. (Mostly!) More complex systems of more lenses using multiple materials yields better performing apo-chromatics & super-apo-chromatics. Invented for microscopes first by Zeiss corporation. Pewaukee Astronomy Club Harken Observatory Flint Glass Crown Glass

30. Yerkes Observatory Williams Bay, WI 40” Refractor 63 foot tube f/19 Built 1897 Illustrates the challenge of a large diameter lens with a long focal length. The same issue arises with a thin lens that also creates a long focal length. Unwieldy and the tube bends. Pewaukee Astronomy Club Harken Observatory

34. Newtonian Reflector Prime Focus Aperture – No Lens Mirror Prime Focus Mirrors don’t have chromatic distortion and curved mirrors can focus. But how do you stick your eye down the tube? Pewaukee Astronomy Club Harken Observatory

35. Newtonian Reflector Aperture – No Lens Primary Mirror Light Bounces off its Top Secondary Mirror Eyepiece Secondary mirror bounces light out a hole in the side. It blocks the light, but it’s not as noticeable as you think (about 10%). Dotted line is unobstructed path to the prime focus, which is inaccessible due to the secondary mirror. Pewaukee Astronomy Club Harken Observatory

37. Isaac Newton’s reflector Pewaukee Astronomy Club Harken Observatory

38. Eyepiece Aperture Spider Finder Scope German Equatorial Mount Clock Drive (disassembled) Counter Weight Secondary Mirror Tube (OTA) Milwaukee Astronomical Society Pewaukee Astronomy Club Harken Observatory

40. Spherical Aberration Perfect Lens Spherical Lens Pewaukee Astronomy Club Harken Observatory

41. Spherical Aberration Perfect Focus Outside Inside Negative Aberration Zero Positive Aberration Pewaukee Astronomy Club Harken Observatory

43. Vertical axis is 1”. The difference between a circle (sphere) and a parabola becomes evident. A hyperbola is even flatter. Pewaukee Astronomy Club Harken Observatory

45. Parabolic Mirror Focal point for off axis (edge) object has a tail like a comet Focal point for on axis (centered) object Eyepiece  Pewaukee Astronomy Club Harken Observatory Field of View 

47. Now, about that eyepiece… MAS A-Scope 112” f/9 Pewaukee Astronomy Club Harken Observatory

48. Cassegrain Reflector Newtonian Reflector Folded optics – tube can be shorter & eyepiece is on bottom Pewaukee Astronomy Club Harken Observatory

52. Coud é Focus Harlan Smith 2.7m Telescope McDonald Observatory Austin, Texas Pewaukee Astronomy Club Harken Observatory

53. Coud é Focus Harlan Smith Telescope - McDonald Observatory, Austin, Texas 4 spectrographs in the basement under the scope can get the light bouncing down from the scope. Pewaukee Astronomy Club Harken Observatory

54. Parabolic Mirror 200” Prime Focus Cassegrain Room below mirror Pewaukee Astronomy Club Harken Observatory Prime Focus Cage

56. Keck 10 meter Telescope Ernie Mastroianni Pewaukee Astronomy Club Harken Observatory

61. Corrector Plate & Secondary   Secondary  Primary  Cassegrain Catadioptric Lens & Mirror shapes vary Pewaukee Astronomy Club Harken Observatory

63. Meade LX200 Schmidt-Cassegrain Aspheric Corrector Plate Convex Secondary Mirror Baffle Tube 12” Spherical Primary Mirror Pewaukee Astronomy Club Harken Observatory

64. Common Catadioptric Designs Easy  Hard : Spherical  Parabolic  Hyperbolic Pewaukee Astronomy Club Harken Observatory Schmidt Cassegrain (SC) Ritchey Chr é tien (RC) Maksutov “ Mak” Corrector Aspheric Aspheric or Flat Convex-Concave or Aspheric Secondary Convex Hyperbola Hyperbola Primary Spherical Hyperbola Spherical Notes Popular for high end amateur (LX200GPS) Common for new high end (LX200R) Very compact Modest apertures

67. Hubble Space Telescope The Most Famous RC of All Pewaukee Astronomy Club Harken Observatory

72. A word from our sponsor… Pewaukee Astronomy Club Harken Observatory

73. Mission Statement The Harken Astronomical Observatory provides education and brings the wonders of our incredible universe to families of our community in the friendly and casual environment of our new library. Pewaukee Astronomy Club Harken Observatory

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