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Types of Telescopes: Refractors Types of Telescopes Refractors
Refractors are what the average person identifies with the word "telescope", a long, thin tube where light passes in a straight line from the front objective lens directly to the eyepiece at the opposite end of the tube.

A classical refractor

Advantages  
  • Easy to use and reliable due to the simplicity of design.
  • Little or no maintenance.
  • Excellent for lunar, planetary and binary star observing especially in larger      apertures.
  • Good for distant terrestrial viewing.
  • High contrast images with no secondary mirror or diagonal obstruction.
  • Color correction is good in achromatic designs and excellent in apochromatic, fluorite, and ED designs.
  • Sealed optical tube reduces image degrading air currents and protects optics.
  • Objective lens is permanently mounted and aligned.

    Optical plan for a refractor
Disadvantages  
  • More expensive per inch of aperture than Newtonians or catadioptrics.
  • Heavier, longer and bulkier than equivalent aperture Newtonians and catadioptrics.
  • The cost and bulk factors limit the practical useful maximum size objective to small apertures
  • Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae because of practical aperture limitations.
  • Focal ratios for traditional refractors are usually long (f/11 or slower) making photography of deep sky objects more difficult.  Short focal-length (fast f/number) apochromats are now available that change this limitation.
  • Some color aberration in achromatic designs (doublet).
  • Poor reputation due to low quality imported toy telescopes; a reputation unjustified when dealing with a quality refractor from a reputable manufacturer.

Information on this page courtesy Celestron’s web site celestron.com
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