Telescopes

Our telescopes | Reflectors | Refractors

The Society's Telescopes

Our primary, original telescope is an 8" Newtonian (reflector), and is a very high quality instrument, especially since its primary mirror was re-silvered early in 1999. The telescope is near St. Aubyn's School on Blundell's Road (see the map). Our chairman, Douglas, is pictured with it below. For details of the telescope's history, click here.

Douglas with the Newtonian at Milestones

In late 2001 and early 2002 we obtained five new instruments (listed below) with our New Opportunities Fund grant from the Lottery Commission. Along with the telescopes, SCS Astro also generously provided us with £350-worth of extras.

Manufacturer & Model	Diameter of primary	Class / Type	Features
Meade LX-90	8.0" mirror	Schmidt-Cassegrain	GOTO system; 30,223-object database
Helios Skyliner 200	8.0" mirror	Dobsonian	-
Meade DS-2114 ATS	4.5" mirror	Newtonian	GOTO system; 1,400-object database
TAL 100-R	4.0" lens	Refractor	-
Orion UltraView 10x50	10x50mm, 10x mag	Binoculars	-

 

     

Two of our newer telescopes

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Reflectors

At the simplest level, all reflecting telescopes involve the use of mirrors to focus light rays (and lenses at the eyepiece), whereas refracting telescopes rely purely upon lenses. The basic characteristics of different optical configurations are charted below, starting with a common one used by most amateur astronomers, the Newtonian. (Information from Illingworth, 1994.) The refractors follow, and then some telescope manufacturers and suppliers.

Inventor	Isaac Newton (English) in 1670
Benefits	Eyepiece mounted on the side of the tube makes the small-primary Newtonian convenient to use for amateurs.
Drawbacks	Eyepiece mounted on the side of the tube makes the large-primary Newtonian inconvenient to use for professionals!
Notes	- Based upon work by Gregory and Zucchi - A 45° prism can be used in place of the diagonal mirror
Inventor	Guillaume Cassegrain (French) in 1672
Benefits	Compact optics make the telescope portable and easy to mount; it is convenient for amateurs, and quite popular.
Drawbacks	Small field of view, primarily due to coma.
Notes
Inventor	James Gregory (a Scottish mathematician) in 1663
Benefits	In the 'aplanatic' Gregorian, coma effects and spherical aberration are eliminated because it uses an ellipsoid primary.
Drawbacks	In the 'aplanatic' Gregorian, a small field of view (limited by astigmatism) is the result of using an ellipsoid primary.
Notes	First compound reflecting telescope.
Inventor	Maksutov (Russian) in 1944
Benefits
Drawbacks
Notes	- Telescope is 'catadioptric': correcting plate is a meniscus lens (deeply curved). - The diagram above illustrates Maksutov-Cassegrain optics; Newtonian and Gregorian configurations are also possible.
Inventor	Bernhard Schmidt (Estonian) in 1930
Benefits	- The telescope is 'catadioptric': the correcting plate eliminates spherical aberration. - The optics provide an extremely large field of view, as illustrated above.
Drawbacks
Notes
Inventor
Benefits
Drawbacks	Small field of view, primarily due to coma
Notes	Any telescope in which light emerges along the polar axis; this means direction is fixed as the observed object follows its path across the sky. Thus, the object can be analysed by large pieces of stationary equipment, set up at the focus.

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Refractors

Inventor	Galileo Galilei (Italian) in 1609
Benefits	Upright image, due to long-focus object lens and powerful diverging lens at eyepiece.
Drawbacks
Notes	- Inspiration came after witnessing Hans Lippershey's 'magic tubes'. - Up to 30x magnification.
Inventor	Johannes Kepler in 1611
Benefits	Larger field of view and greater magnification than Galilean optics can provide.
Drawbacks	Small field of view, primarily due to coma
Notes	Inverted image, with more powerful object lens and and another convex lens at the eyepiece.

Telescope manufacturers / suppliers

Meade
Celestron

SCS Astro
Orion Optics
David Hinds Ltd
BC & F Telescope House