page_title: Newtonian telescope
section_title: Advantages of the Newtonian design
hierarchical_section_title: Newtonian telescope / Advantages of the Newtonian design
caption_attribution_description: Newtonian scope.
context_page_description: The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design has made it very popular with amateur telescope makers.
context_section_description: They are free of chromatic aberration found in refracting telescopes.
  Newtonian telescopes are usually less expensive for any given objective diameter (or aperture) than comparable quality telescopes of other types.
  Since there is only one surface that needs to be ground and polished into a complex shape, overall fabrication is much simpler than other telescope designs (Gregorians, cassegrains, and early refractors had two surfaces that need figuring. Later achromatic refractor objectives had four surfaces that have to be figured).
  A short focal ratio can be more easily obtained, leading to wider field of view.
  The eyepiece is located at the top end of the telescope. Combined with short f-ratios this can allow for a much more compact mounting system, reducing cost and adding to portability.
caption: Newtonian optical assembly showing the tube (1), the primary mirror (2), and the secondary diagonal mirror support (also called a "spider support") (3).
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