- Shop
at optical specialty stores, and try to avoid purchasing
a telescope
at department stores.
- Stray
away from telescopes advertised based on power of
magnification (ie 250x or 400 power). Most
observing magnification with a beginner scope is between
50-125 power (50X-125X). This is more than enough
to let you see great views of craters on the Moon,
the rings of Saturn, and the moons of Jupiter. Magnification
can be changed by changing eyepieces.
- Quality
manufacturing! Avoid plastic and look for
metal and wood construction.
- Know
the mount: Make sure the telescope connects
solidly with the tripod -- no wiggles or vibrations.
The scope should scan steadily and smoothly.
- Pay
attention to the diameter or aperture of the main
(primary) lens or mirror which collects the incoming
starlight. The bigger the mirror (or lens), the more
light is collected.
The more light
collected means fainter objects can be seen. A point
to keep in mind however is, the larger the mirror,
the larger the telescope, which can make it difficult
to move out to the driveway, or drag out to the backyard.
It may not even fit easily inside your car to transport
to a dark sky location or star party.
- Reflecting
telescopes are good for beginners, particularly the
simple Dobsonian style "Dobs"
are easy to set up and provide quality optics and
sturdy mounts. A 6- to 10-inch diameter is recommended.
This measurement is the diameter of the primary mirror
or lens, not the tube of the telescope.
Types
of Telescopes
There three common types of telescopes: refractors,
Newtonian reflectors,
and catadioptrics.
Refractors use a lens at the front of the telescope
to gather light, which is sent to the eyepiece at the
back. Newtonian reflectors use a large mirror at the
back of the telescope to gather light, which is reflected
back up towards the front of the telescope. From there
it reflected out the side of the tube to the eyepiece.
Catadioptrics are hybrids, with a correcting lens at
the front, and a mirror at the back. All
three are highly efficient systems but they all have
their pros and cons.
1. Refractors (Lens based scopes)
These are the most commonly seen telescopes. Refractors
work by using an objective lens to bend light. If the
optics are good this results in a very sharp picture
with high contrast. The three types of refractors are
non-achromatic, achromatic, and apochromatic. Their
biggest drawback tends to be their heavy weight. A serious
consideration if you are looking for portability.
- Non-achromatic
refractors
They use one or two convex lenses to focus light.
They have severe chromatic aberration because they
do not focus all colors of light in the same spot
which gives them terrible views. These are your typical
department store refractors. They are very cheap in
price but they are almost useless for astronomy. Non-achromatic
refractors are best avoided.
- Achromatic
refractors
They use a concave and a convex lens to bend light.
This ensures that most colors of light focus at the
same point. These telescopes have sharp views and
good contrast but, they are very expensive for their
aperture. For about $800.00 the largest refractor
you could get would be about three inches which would
be an O.K. plantary viewing telescope but it would
be almost useless for deep-space viewing. Also, these
telescopes tend to give you blue halos around the
stars.
- Apochromatic
refractors
They use two lenses shaped like an achromatic refractors
except they are made of two different types of glass
which allows them to focus all colors of light at
the same spot. These telescopes give without a doubt,
the sharpest views and the highest contrast. They
have a big drawback though, they are very expensive
at usually four digit price tags.
2.
Newtonian Reflector (mirror based scopes)
These
telescopes give you the most aperture for the dollar.
A Newtonian reflector uses mirrors to reflect and focus
light on a converged point. Newtonian reflectors give
very sharp views with almost as much contrast as an
achromatic reflector. These telescopes are good for
any astronomical use you may have for them. A reflector
is the most cost effective telescope you can buy. Prices
vary greatly depending on the type of mount and gadgets
included ie. motors.
Dobsonians
(a sub-species of Newtonians)
A Dobsonian is a basic Newtonian telescope on a very
simple, stable, and easy-to-use alt-azimuth mount. The
mount is made of solid but very inexpensive materials
(usually plywood and formica), so that most of the money
you spend buys optics. This means that you can get a
larger aperture, or higher quality optics, for a give
amount of money. The drawback is that the mount can
not be made to track the motion of the sky automatically
without making expensive modifications. Most people
do not find this to be a problem in practice, and many
find the simple up-down left-right motions of the alt-azimuth
mount easier to use than the polar-oriented motions
of an equitorial. Price tags range form about $ 400
for a 6 incher to $ 800 for a large 10 inch diameter
dob.
3.
Catadrioptic (Mirror-lens combo scopes)
- Schmitt
Cassegrain
It combines a refractor and a reflector in one package.
The resulting telescope is extremely portable, compact
and user friendly. There is a drawback to these telescopes
though; they are very expensive ($500 + ) and they
have less contrast than other types of telescopes
except the non-achromatic refractor. These make a
good choice if compactness, portability and user friendliness
are your prime consideration. Lately leading manufacturers
provide these scopes with onboard computers which
can move the scope automatically to any target in
its database. Of course this option jacks the price
quite a bit. Price tags range from $ 1000 for a simple
8 inch to $ 6000 for a gigantic 14 incher with all
the gizmos.
- Maksutov
Telescopes of this design are basically the same as
Schmitt Cassegrains except their corrector plate is
curved which allows greater contrast and a flatter
field.
Leading
Manufacturers
Recommended
Reading Links
Local
Astronomy Shops:
La
Maison de l'Astronomie - downtown-eastend
Lire
La Nature - south shore
Focus
Scientific - Great Ottawa Shop
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