Newtonian Telescope

The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton (1643-1727), using a parabolic primary mirror and a flat diagonal secondary mirror. Image File history File links Simple Diagram of a Newtonian Telescope created by TMoore using MSPaint. ... Image File history File links Simple Diagram of a Newtonian Telescope created by TMoore using MSPaint. ... Ritchey 24 reflecting telescope A reflecting telescope (reflector) is an optical telescope which uses mirrors, rather than lenses, to reflect light. ... Sir Isaac Newton in Godfrey Knellers 1689 portrait Sir Isaac Newton (25 December 1642 – 20 March 1727 by the Julian calendar in use in England at the time; or 4 January 1643 – 31 March 1727 by the Gregorian calendar) was an English physicist, mathematician, astronomer, philosopher, and alchemist who... A parabolic reflector (also known as a parabolic dish or a parabolic mirror) is a reflective device formed in the shape of a paraboloid of revolution. ...

Advantages of the Newtonian Design

• Newtonians are usually less expensive for any given aperture than comparable quality telescopes of other types.

• A high quality primary mirror can be made by hand by amateur astronomers

• A short focal length can be obtained, leading to wide field, bright views.

• Long focal length Newtonian telescopes can give excellent planetary views.

• There is no chromatic aberration caused by lenses as in a refractor

• The eyepiece is at the top end of the telescope, allowing for a shorter and more stable mount.

• The heavy primary mirror is at the bottom allowing for large portable scopes. Dobsonian mounted Newtonians can have a 40" primary mirror.

• Collimation is relatively easy.

A replica of Newton's first 6 inch reflector

Amateur astronomy, often called back yard astronomy, is a hobby whose participants enjoy observing celestial objects. ... The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ... Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. ... The 50 cm refractor at Nice Observatory. ... In astronomy the Dobsonian is a type of telescope mounting that became popular in the 1980s for its extreme simplicity, low price, and rugged construction. ... Collimated light is light whose rays are parallel. ... Download high resolution version (1024x891, 118 KB)A replica of Isaac Newtons telescope of 1672. ... Download high resolution version (1024x891, 118 KB)A replica of Isaac Newtons telescope of 1672. ...

Disadvantages of the Newtonian Design

• Newtonians have coma, which is blurring of images away from the optical center. This problem is worse the shorter the focal length. Newtonians with a focal length of f/6 or higher are considered to have little to no coma. Newtonians of a focal length of less than f/4 are often considered to have too much coma.

• Newtonians have a central obstruction due to the secondary mirror in the light path. This obstruction and the diffraction spikes caused by the support structure (called the spider) of the secondary mirror reduces contrast. Visually, these effects can be eliminated by using a two or three-legged curved spider. Although a four-legged spider causes less difraction that a three-legged curved spider, the three-legged curved spider often gives a more aestheticly pleasing view.