|
A refracting telescope (refractor) is a telescope which uses lenses to refract light. This refraction causes parallel light rays to converge at a focal
point; while those which were not parallel converge upon a focal plane. This can enable a user to view a distant object as if it were brighter, clearer, and/or larger. These are similar to microscopes. The
monocular is a type of refractor. A typical refractor has two lenses, an objective lens and an eyepiece lens. The objective lens has
two pieces of glass (with different densities), "crown" and "flint glass". Each side of each piece is ground and polished,
and then the two pieces are glued together. The curvatures are designed to cancel chromatic and spherical aberration.
Technical Difficulties
For research purposes, refracting telescopes have become unpopular. They are
criticized for their relatively high-degree of chromatic
and spherical aberration. There is also the problem of
lens sagging, a result of
gravity affecting glass. There is a further
problem of mis-refraction; caused by air bubbles
trapped within the lenses. In addition, glass is opaque to certain wavelengths, and even visible
light is dimmed when it passes through glass. Many of these problems are avoided by using reflecting telescopes.
Notable Refracting Telescopes
See also:
From Refractor telescope to be merged :
A refractor telescope is a type of optical
telescope that refracts light through a pair of lenses on either end of the
telescope. While initially the most common type of telescope, these are today used primarily by amateur astronomers, and have been supplanted in professional
work by reflecting telescopes. However, some relatively
small instruments with 100-150mm objective lenses regularly produce
astrophotography that rivals images created by professionals as
recently as 20 years ago using what were then the largest telescopes on
Earth.
See also: List of largest optical refracting telescopes (from which it is clear that
their heydey was in the 19th century)
|