optics, the refractor telescope is also the basic instrument
for the amateur astronomer. There are many varieties, the most
common to the most specialized, depending on their application
in astronomy. Monoculars, unique and constant magnification,
are integral register part of refractor telescopes. Composed
of a more or less complex objective, whether in the material
choice or in the number of lenses, the refractor telescope is
commonly with a objective in two adjoining lenses : a bi-convex
lens crown and flint lens having a concave face and the other
very slightly convex. This composition can correct the lens chromatic
aberration, which were assigned the refractor telescopes to the
the optical era beginning.
Their main advantages
are the lack of central obstruction, which predispose them to
planetary high resolution imaging and a closed tube making them
much less susceptible to turbulence as reflector telescopes.
is their price :
- At least three
times more expensive than the same diameter reflector telescopes.
invented later than refractor telescopes, reflector telescopes
and optical composition take the name of their designer. The
objective has been replaced by a concave or parabolic mirror,
responsible for collecting the light of the stars. In all reflector
telescopes, the primary mirror is assisted by another mirror,
responsible for directing the collected light to the eyepiece,
which is characterized by a more or less central obstruction.
This is the common choice for the amateur to the first economic
criterion (a reflector telescope costs on average three times
less than the refractor telescope). However, against-part of
this economy, its user will have to learn to regularly adjust
its instrument (collimation).
The classic Newton
telescope 114/900. The concave primary mirror, placed at bottom
of the tube, reflects the light towards a secondary mirror plane
inclined at 45 ° brings out the light on the intrument side.
I have used for
ten years a Schmidt Cassegrain telescope to observe the moon
and realize my planetary images. It is a versatile telescope
oriented to the global high-resolution. Very compact, most of
these telescopes have a F / D ratio of 10 with a focal length
of about 2 meters for a tube which does not exceed 50 cm long
! This is a catadioptric telescope. It combines the use of lenses
and mirrors. In the telescope case, the light first passes through
a thin corrector plate whose faces are aspherical, so as to slightly
deflect the light. Then the parabolic primary mirror, the bottom
of the tube, in turn focuses the light toward the convex secondary
mirror that brings out the light in the back of the tube, through
the primary mirror.