Schmidt Cassegrain telescope
Tube
Keeps moisture and dirt off image
Light rays
on
n
or
How a telescope works
Types of telescopes
Eyepiece
Refractors: Use glass lenses
Reflectors: Use mirrors instead of lenses
Lens magnifies
image
Mirror
The objective lense (refractor) or primary mirror (reflector)
collects the light from distant objects and directs them to
a focal point.
Primary mirror
The eyepiece takes the light from a small image and spreads
it out over the eye’s retina. This makes the image appear larger.
Types of telescopes
Aperture: The aperture, or opening of the telescope,
determines the amonut of light it collects. The larger the
opening, the brighter the image. This is the most important
feature of the telescope.
Magnification: This is determined by the number of lenses in
the eyepiece.
Hans Lippershey, of
Middleburg,Holland,
invented the first telescope,
a refractor, in 1607. It was
initially used by the military.
Newton’s
telescope
The reflector telescope
was developed by
Sir Isaac Newton.
Galileo was the first to
use the telescope for
astronomy.
Refractor
Eyepiece
This is the type telescope
Galileo used. Its main
problem is chromatic
aberration.
Concave lens
Objective lens
(Convex)
Reflector
Lens
This telescope, developed by Isaac Newton, overcomes the problem of chromatic aberration
through the use of mirrors.
Eyepiece
Chromatic aberration
Colors traveling through a lens are bent at
an angle, causing a rainbow. Blue bends
at a sharper angle than red and focuses
at a different point. This is chromatic
aberration. Adding a second lens causes
the light to focus on the same point.
Mirror
Lens
Plane mirror
(Concave)
Light rays
Light rays
Red focus
bj
Light rays
Lens
A
Blue focus
Red and blue
focus focus
Light rays
Two
lenses
Mounts
Types
Alt-azimuth: Has a horizontal and vertical axis. Set horizontal and vertical coordinates and
then lock in. Inexpensive.
Equatorial: More complicated. Must be aligned with the Earth’s poles. Often equipped with
counterweight. Can track path of objects across the sky. More expensive.