Schmidt-Newton telescope
Encyclopedia
A Schmidt–Newton telescope is a catadioptric telescope that combines elements from both the Schmidt camera
and the Newtonian reflector
. In this telescope design a spherical primary mirror
is combined with a Schmidt corrector plate
, making system that has less spherical aberration
(coma
) than a reflecting telescope with a parabolic mirror
. The design uses a 45° flat secondary mirror to view the image giving it the optical path of a Newtonian telescope.
than Newtonian telescopes of the same focal ratio (usually about half). The corrector plate also helps seal the tube assembly from air currents and provides mounting point for the diagonal mirror, eliminating the diffraction effects from a "spider" secondary support. The all spherical surfaces are much easier to manufacture, especially in short focal ratios. Telescopes using this design have a short focal ratio of around f/4 making them well suited for astrophotography or CCD
imaging. Schmidt–Newtonians also costs less than the more commonly produced Schmidt–Cassegrains since they don't have the added curved secondary mirror
or the complicated primary mirror focusing mechanism found in most Schmidt–Cassegrain designs.
Currently, Meade Instruments is the only commercial manufacturer of Schmidt–Newtonian telescopes, offering 6, 8, and 10-inch models on its LXD-75 "GO-TO
" equatorial mount.
Schmidt camera
A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
and the Newtonian reflector
Newtonian telescope
The Newtonian telescope is a type of reflecting telescope invented by the British 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...
. In this telescope design a spherical primary mirror
Primary mirror
A primary mirror is the principal light-gathering surface of a reflecting telescope.-Description:The primary mirror of a reflecting telescope is a spherical or parabolic shaped disks of polished reflective metal , or in later telescopes, glass or other material coated with a reflective layer...
is combined with a Schmidt corrector plate
Schmidt corrector plate
A Schmidt corrector plate is an aspheric lens which is designed to correct the spherical aberration in the spherical primary mirror it is combined with. It was invented by Bernhard Schmidt in 1931, although it may have been independently invented by Finnish astronomer Yrjö Väisälä in 1924...
, making system that has less spherical aberration
Spherical aberration
thumb|right|Spherical aberration. A perfect lens focuses all incoming rays to a point on the [[Optical axis|optic axis]]. A real lens with spherical surfaces suffers from spherical aberration: it focuses rays more tightly if they enter it far from the optic axis than if they enter closer to the...
(coma
Coma (optics)
In optics , the coma in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted, appearing to have a tail like a comet...
) than a reflecting telescope with a parabolic mirror
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
. The design uses a 45° flat secondary mirror to view the image giving it the optical path of a Newtonian telescope.
Advantages
Schmidt–Newtonian telescopes offer images with less comaComa (optics)
In optics , the coma in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted, appearing to have a tail like a comet...
than Newtonian telescopes of the same focal ratio (usually about half). The corrector plate also helps seal the tube assembly from air currents and provides mounting point for the diagonal mirror, eliminating the diffraction effects from a "spider" secondary support. The all spherical surfaces are much easier to manufacture, especially in short focal ratios. Telescopes using this design have a short focal ratio of around f/4 making them well suited for astrophotography or CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
imaging. Schmidt–Newtonians also costs less than the more commonly produced Schmidt–Cassegrains since they don't have the added curved secondary mirror
Secondary mirror
A secondary mirror is the second deflecting or focusing mirror element in a reflecting telescope. Light gathered by the primary mirror is directed towards a focal point typically past the location of the secondary. Secondary mirrors in the form of an optically flat diagonal mirror are used to...
or the complicated primary mirror focusing mechanism found in most Schmidt–Cassegrain designs.
Currently, Meade Instruments is the only commercial manufacturer of Schmidt–Newtonian telescopes, offering 6, 8, and 10-inch models on its LXD-75 "GO-TO
GoTo (telescopes)
In amateur astronomy, "GoTo" refers to a type of telescope mount and related software which can automatically point a telescope to astronomical objects that the user selects...
" equatorial mount.