What’s the difference between Refractor and Reflector?

Q. What’s the difference between Refractor and Reflector?

A. Thank you to Celestron for the following information;

Refracting Telescopes

  • Refractors use an objective lens to refract or bend light to a point
  • Offers highest contrast images of any telescope design
  • Perfect for astronomical or terrestrial viewing

Disadvantages – Very expensive to produce in apertures over 100 mm, can suffer from chromatic aberration - a violet or yellowish halo around a bright target.

There are two basic types of refracting telescopes

  • Achromatic – Uses a two element objective (a doublet) that brings red and blue light to focus as closely as possible.
  • Apochromatic  - Uses a three element objective (a triplet) that brings red, blue, and violet to focus as closely as possible.  The third element is usually made of a special fluorite or ED glass.

Newtonian Reflecting Telescopes

  • Reflectors use a spherical or parabolic objective mirror to focus light
  • Light enters the tube, striking the primary mirror, reflects back up the tube to a flat secondary mirror and exits out of the side of the tube into the eyepiece
  • Mirrors must be collimated (aligned perfectly) to give the sharpest image
  • Contrast is lower due to central obstruction caused by the secondary mirror
  • Perfect for astronomical viewing, but not recommended for terrestrial as this design yields a “rotated” image