Astronomical telescopes are divided into subgroups. All telescopes work by collecting electromagnetic radiation and focussing it into an image which may be seen or photographed. The purpose is to see things which are far away in the universe.

The traditional types all work to collect visible light from the sky. Recent types may work outside the visible spectrum. They all have their different advantages and disadvantages and they are used in different areas of astronomy.

Dioptrics. Telescopes which create their image with an objective that is a convex lens (refractors) are said to be "dioptric" telescopes.

• Achromatic: uses convex and concave lenses together, to correct for chromatic aberration.
  • Apochromatic: a more complex arrangement, for even less chromatic aberration.
• Non-achromatic
• Binoculars

Catoptrics. Optical systems using mirrors: uses reflected light to form the image.

• Newtonian
• Gregorian
• Cassegrain
• Herschelian telescope

Catadioptric telescopes use corrector lenses to fix problems in a reflector.

• Schmidt telescope
• Maksutov telescope

• Čerenkov radiation telescope used to detect gamma rays
• Infrared telescope
• Radio telescope
• Submillimeter telescope
• Ultraviolet light telescope (for Ultraviolet astronomy)
• X-ray telescope (for X-ray astronomy)
  • Wolter telescope