Select from one of the following to learn more about
the different telescope mounts.
The Classic
Altitude-Azimuth Mount
Frequently referred to as alt-azimuth or just alt-az, this class
of telescope mount is one of the simplest types available. As the
name implies, an alt-az mount has a altitude axis that moves
vertically and a azimuth axis that moves horizontally. One example
of the classic alt-az mount can be found in a simple camera tripod.
 The
Dobsonian Mount
Back in the 1970s, sidewalk astronomer John Dobson, designed a
variation of the alt-az mount which today is known as the Dobsonian
mount or just Dobsonian. The Dobsonian mount has become extremely
popular among the amateur astronomers of today. Dobson wished to
create a mount that would support the large simple to make Newtonian
reflectors he was making. Dobson also wished that the mount be
simple to make using only commonly available materials like plywood,
Teflon, Formica, glue, nails and screws. The resulting Dobsonian
mount was easy to build, setup and use.
The down side of Altitude-Azimuth Mount
Though both the traditional alt-az and Dobsonian mounts are
wonderfully easy to use, they also possess a drawback. Remember that
the Earth is turning on its axis. This means that the objects in the
sky appear to move throughout the night. As the telescope is moved
more easterly or more westerly, it becomes necessary to nudge the
telescope from time to time in both horizontal and vertical axis to
keep the
viewed object in the eyepiece. For longer viewing runs of any
object, this nudging can become a little tiring.
Equatorial Mounts
The equatorial mount is much harder to understand then its
simpler alt-az cousin. Like the alt-az mount, the equatorial mount
is made up of two perpendicular axis known as the right ascension
(or polar) axis and the declination axis. Both axis are tilted at an
angle that matches your location's latitude and the right ascension
axis must be aligned with the celestial pole. A small motor is often
placed onto the right ascension axis. When the equatorial mount as
setup correctly, this small motor drives the right ascension axis to
counteract the earth's rotation. This keeps any viewed object in the
scope's eyepiece through the night. The motorized Equatorial Mount
is the preferred mount for astronomers wishing to view objects for
long periods of time or capturing images using some type of camera
system. There are two general types of equatorial mounts in use
today.
The German Equatorial Mount
For many years, the German equatorial mount has been a favorite
among amateur astronomers around the world. Today this type of mount
can be found on many of the more popular refractor and reflector
models. The German equatorial allows free access to just about any
part of the sky and is easily outfitted with a clock drive to offset
the Earth's movement.
There are several flaws with the German equatorial mounts. First
it is impossible to sweep continuously from east to west in one
movement. As the telescope nears the meridian, the user must move it
away from whatever was being viewed so that the telescope can be
swung around to
the other side of the mount and re-centered on the target. A major
problem for anyone doing a long astrophotography run. The second
problem with the German mount is its weight. The mount alone can
weigh from 30 to over 100 pounds. Most of the weight is in the axis
counterweights
used to offset the telescope's weight. A user who wishes to
transport his/her mount should have a strong back.
 The
Fork Equatorial Mount
Although German mounts are the preferred choice for telescopes
with long tubes, the fork equatorial mount is usually found on the
more compact telescopes like the Schmidt-Cassegrain. In a fork
mount, the telescope is mounted between two short tines which define
the declination axis. The tines typically extend from a rotating
circular base which is tilted to your location's latitude. The
titled axis makes up the right ascension axis.
The fork equatorial mount is for users who need to transport
their telescopes a lot. In most cases, the telescope does not need
to be removed from the mount for transportation. There are no
counterweights on a fork equatorial, making the over all telescope
weight far less than the equivalent German equatorial telescope. The
overall telescope is reduced to a manageable weight and size.
There is one major flaw in the fork equatorial mount. As the
telescope is pointed closer to the celestial pole, the eyepiece
becomes notoriously difficult to get at. With some fork mounted
telescopes, it can be next to impossible for an astrophotography to
take images at the celestial pole. |
