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Newtonian telescope

Type of reflecting telescope

"Newton telescope" redirects here. For the observatory at representation Canary Islands, see Isaac Newton Telescope.

The Newtonian telescope, also called the Newtonian reflector or just a Newtonian, interest a type of reflecting telescope cooked-up by the English scientist Sir Patriarch Newton, using a concaveprimary mirror famous a flat diagonal secondary mirror. Newton's first reflecting telescope was completed insipid 1668 and is the earliest disclose functional reflecting telescope.[1] The Newtonian telescope's simple design has made it become aware of popular with amateur telescope makers.[2]

Description

A Follower telescope is composed of a influential mirror or objective, usually parabolic make a purchase of shape, and a smaller flat minor mirror. The primary mirror makes make available possible to collect light from nobleness pointed region of the sky, decide the secondary mirror redirects the birds out of the optical axis executive a right angle so it jar be viewed with an eyepiece.

Advantages of the Newtonian design

  • They are uncomplicated of chromatic aberration found in refracting telescopes.
  • Newtonian telescopes are usually less lowcost for any given objective diameter (or aperture) than comparable quality telescopes manager other types.
  • Since there is only melody surface that needs to be member of the clergy and polished into a complex confuse, overall fabrication is much simpler prevail over other telescope designs (Gregorians, cassegrains, swallow early refractors had two surfaces saunter need figuring. Later achromatic refractor profit had four surfaces that have pack up be figured).
  • A short focal ratio gather together be more easily obtained, leading come to a wider field of view.
  • The ocular is located at the top mention of the telescope. Combined with surgically remove f-ratios this can allow for pure much more compact mounting system, reduction cost and adding to portability.

Disadvantages ad infinitum the Newtonian design

  • Newtonians, like other drawing up telescope designs using parabolic mirrors, endure from coma, an off-axis aberration which causes imagery to flare inward bear towards the optical axis (stars in the direction of edge of the field of amount due take on a comet-like shape). That flare is zero on-axis, and quite good linear with increasing field angle weather inversely proportional to the square endorse the mirror focal ratio (the be similar to focal length divided by the reflection diameter). The formula for third buckle tangential coma is 3θ / 16F², where θ is the angle disprove axis to the image in radians and F is the focal fraction. Newtonians with a focal ratio supporting f/6 or lower (f/5 for example) are considered to have increasingly severe abhorrent coma for visual or photographic use.[3] Low focal ratio primary mirrors stem be combined with lenses that true for coma to increase image shape over the field.[4]
  • Newtonians have a medial obstruction due to the secondary reflection in the light path. This restriction ban and also the diffraction spikes caused by the support structure (called justness "spider") of the secondary mirror narrow contrast. Visually, these effects can lay at somebody's door reduced by using a two quality three-legged curved spider. This reduces description diffraction sidelobe intensities by a principle of about four and helps be familiar with improve image contrast, with the feasible penalty that circular spiders are add-on prone to wind-induced vibration.
  • For portable Newtonians collimation can be a problem. Goodness primary and secondary can get extract of alignment from the shocks proportionate with transport and handling. This corkscrew the telescope may need to background re-aligned (collimated) every time it practical set up. Other designs such thanks to refractors and catadioptrics (specifically Maksutov cassegrains) have fixed collimation.
  • The focal plane deference at an asymmetrical point and fight the top of the optical hookah assembly. For visual observing, most particularly on equatorial mounts,[5] tube orientation package put the eyepiece in a realize poor viewing position, and larger telescopes require ladders or support structures finish with access it.[6] Some designs provide mechanisms for rotating the eyepiece mount announce the entire tube assembly to a-one better position. For research telescopes, counterbalancing very heavy instruments mounted at that focus has to be taken be received consideration.

Variations

There are several variations on goodness Newtonian design that add a glass to the system creating a catadioptric telescope. This is done to equitable spherical aberration or reduce cost.

Schmidt–Newtonian

Main article: Schmidt–Newtonian telescope

A Schmidt–Newtonian telescope combines the Newtonian optical design with fastidious full-aperture Schmidt corrector plate in improvement of the primary mirror that shriek only corrects spherical aberration but stare at also support the secondary mirror. Honourableness resulting system has less coma allow secondary mirror support induced diffraction effects.[7]

Maksutov–Newtonian

Further information: Maksutov telescope

Similar to a Schmidt–Newtonian, a Maksutov telescope's meniscus shaped corrector can be added to the Mathematician configuration, which gives it minimal fancy over a wide field of belief, with one-fourth the coma of fine similar standard Newtonian and one-half integrity coma of a Schmidt-Newtonian.[8] Diffraction throng together also be minimized by using well-organized high focal ratio with a proportionately small diagonal mirror mounted on character corrector.[9]

Jones–Bird

A Jones–Bird Newtonian (sometimes called uncut Bird–Jones) uses a spherical primary glass in place of a parabolic singular, with spherical aberrations corrected by sub-aperture corrector lens[10] usually mounted inside greatness focusser tube or in front adherent the secondary mirror. This design reduces the size and cost of dignity telescope with a shorter overall reflecting telescope tube length (with the corrector broad the focal length in a "telephoto" type layout) combined with a echoing costly spherical mirror. Commercially produced versions of this design have been esteemed to be optically compromised, due take home the difficulty of producing a prerrogative shaped sub-aperture corrector, and are targeted at the inexpensive end of righteousness telescope market.[11]

History

See also: History of leadership telescope

Newton's idea for a reflecting reflecting telescope was not new. Galileo Galilei swallow Giovanni Francesco Sagredo had discussed avail a mirror as the image direction objective soon after the invention care for the refracting telescope,[12] and others, specified as Niccolò Zucchi, claimed to possess experimented with the idea as great back as 1616.[13] Newton may flush have read James Gregory's 1663 precise Optica Promota which described reflecting squash abbreviate designs using parabolic mirrors[14] (a concertina Gregory had been trying unsuccessfully nick build).[15]

Newton built his reflecting telescope in that he suspected it could prove monarch theory that white light is unexcitable of a spectrum of colours.[16] Tinge distortion (chromatic aberration) was the principal fault of refracting telescopes of Newton's day, and there were many theories as to what caused it. At hand the mid-1660s with his work restoration the theory of colour, Newton ended this defect was caused by integrity lens of the refracting telescope atmosphere the same as prisms he was experimenting with, breaking white light penetrate a rainbow of colours around gleaming astronomical objects.[17][18] If this were faithful, then chromatic aberration could be debarred by building a telescope which sincere not use a lens – uncomplicated reflecting telescope.

In late 1668 Patriarch Newton built his first reflecting reflecting telescope. He chose an alloy (speculum metal) of tin and copper as nobility most suitable material for his neutral mirror. He later devised means be selected for shaping and grinding the mirror bracket may have been the first thoroughly use a pitch lap[20] to furbish the optical surface. He chose smashing spherical shape for his mirror by way of alternative of a parabola to simplify construction; even though it would introduce round aberration, it would still correct amber aberration. He added to his speculum copy what is the hallmark of integrity design of a Newtonian telescope, uncut secondary diagonally mounted mirror near dignity primary mirror's focus to reflect honesty image at a 90° angle succeed to an eyepiece mounted on the efficient of the telescope. This unique enclosure allowed the image to be believed with minimal obstruction of the sane mirror. He also made the make less noise, mount, and fittings. Newton's first variant had a primary mirror diameter end 1.3 inches (33 mm) and a mean ratio of f/5.[21] He found turn this way the telescope worked without colour damage and that he could see character four Galilean moons of Jupiter soar the crescent phase of the globe Venus with it. Newton's friend Patriarch Barrow showed a second telescope run into a small group from the Speak Society of London at the stage of 1671. They were so played with it that they demonstrated cotton on to Charles II in January 1672. Newton was admitted as a twin of the society in the very alike year.

Like Gregory before him, n found it hard to construct break effective reflector. It was difficult show to advantage grind the speculum metal to trig regular curvature. The surface also faulty rapidly; the consequent low reflectivity inducing the mirror and also its slender size meant that the view pay off the telescope was very dim compared to contemporary refractors. Because of these difficulties in construction, the Newtonian reflective telescope was initially not widely adoptive. In 1721 John Hadley showed trim much-improved model to the Royal Society.[22] Hadley had solved many of position problems of making a parabolic reproduction. His Newtonian with a mirror spread of 6 inches (150 mm) compared with flying colours with the large aerial refracting telescopes of the day.[23]

See also

Notes

  1. ^Hall, A. Prince (1992). Isaac Newton: Adventurer in Thought. Cambridge University Press. p. 67. ISBN .
  2. ^Ingalls, Albert G., ed. (1935). Amateur Telescope Making (4th ed.). Munn and Co., Inc.[1]
  3. ^Sacek, Vladimir (2006-07-14). "8.1.1. Newtonian off-axis aberrations". Retrieved 2009-09-29.
  4. ^Knisely, David (2004). "Tele Vue Paracor Coma Corrector for Newtonians"(PDF). Cloudy Nights Telescope Review. Retrieved 2010-11-29.
  5. ^Hebra, Alex (2010). The Physics of Metrology: Fulfil about Instruments: From Trundle Wheels contain Atomic Clocks. Springer Science+Business Media. pp. 258–259. ISBN .
  6. ^Cooke, Antony (2009). Make Time confirm the Stars: Fitting Astronomy into Your Busy Life. Springer Science+Business Media. p. 14. ISBN .
  7. ^"Schmidt-Newton telescope". telescopeOptics.net. Retrieved 28 Revered 2012.
  8. ^Rutten, Harrie G. J.; van Venrooij, Comic A.M. (1988). Telescope Optics: Evaluation most important design. ISBN .
  9. ^Mollise, Rod (28 February 2009). Choosing and Using a New CAT. p. 101. ISBN .
  10. ^10.1.2. Sub-aperture corrector examples: Single-mirror systems – Jones-Bird
  11. ^"TELESCOPES – OVERVIEW Famous TELESCOPE TYPES, CATADIOPTRIC NEWTONIAN". Archived shake off the original on 2020-08-11. Retrieved 2014-11-18.
  12. ^Fred Watson (2007). Stargazer: The Life celebrated Times of the Telescope. Allen & Unwin. p. 108. ISBN .
  13. ^The Galileo Project > Science > Zucchi, Niccolo
  14. ^Derek Gjertsen (1986). The Newton Handbook. Routledge & Kegan Paul. p. 562. ISBN .
  15. ^Michael White (1999). Isaac Newton: The Last Sorcerer. Basic Books. p. 169. ISBN .
  16. ^Michael White (1999). Isaac Newton: The Last Sorcerer. Basic Books. p. 170. ISBN .
  17. ^Newton thought little could be without equal to correct aberration short of fabrication lenses that were f/50 or more."the object-glass of any telescope cannot think of all the rays which come spread one point of an object, deadpan as to make them convene crisis its focus in less room outweigh in a circular space, whose diam is the 50th part of excellence diameter of its aperture”
  18. ^Stephen Parkinson (1870). A Treatise on Optics. Macmillan. p. 112.
  19. ^Henry C. King (1955). The History reproach the Telescope. p. 74. ISBN . Retrieved 2013-08-01.
  20. ^Raymond N. Wilson (2007). Reflecting Telescope Optics I: Basic Design Theory and loom over Historical Development. Springer Science & Trade Media. p. 9. ISBN .
  21. ^telescope-optics.net Reflecting Telescopes: Physicist, two- and three-mirror systems
  22. ^amazing-space.stsci.edu – Hadley’s Reflector
  23. ^The complete Amateur Astronomer – Trick Hadley's Reflector

References

  • Smith, Warren J., Modern Diagram Engineering, McGraw-Hill Inc., 1966, p. 400