A telescope is an optical
device that makes distant dim objects appear larger and brighter.
The most popular form of telescope, called a Newtonian, uses a
paraboloidal mirror to focus light onto an image plane that is then
inspected by an eyepiece to gain magnification. The
paraboloidal mirror, and smaller flat secondary that is used to
direct light out to the side of the tube, must be ground, polished,
and figured to an accuracy of a couple of millionths of an inch.
That amateurs can do this by hand using simple test equipment is
nothing short of amazing. Also amazing is the degree of penetration
into the sky that amateurs now achieve. Using a CCD camera and
12 inch aperture telescope, an amateur can equal the 200 inch Palomar
telescope with film plates. Digital cameras with cooled
detectors must be exposed for many minutes to capture extremely faint
objects. During the exposure, the camera and telescope must
precisely follow the stars in their slow apparent motion across the
sky.