You Purchase a Telescope You Should Consider:
Remember large telescopes are very heavy, the
telescope that is easiest to set up is the one that will get used the
Remember no matter what telescope you purchase
you ar not going to see anything like what you see on the NASA website
or on calenders and posters. Those images were taken by multi-million dollar
equipment, generally from space. You will be able to see planets and
the Orion Nebula through an amature telescope but anything else may
just look like a ball of light.
For this reason concentrate on viewing the
planets. They are incredibly beautiful and never fail to
please. The planets are breathtaking through even the smallest
telescopes and binoculars.
- A good scope will not talk about its Power: If the box blares "300X" or other numbers about
the ?Power? the scope within has, Caution! High power sounds great,
but, there?s a catch. While high magnification makes an object appear
larger, light gathered by the scope is spread over a larger area
creating a fainter image. Also, "high-powered" scopes have restrictions
of the eyepiece design, which may limit how much of the large image you
can actually see. Sometimes, lower power provides a better viewing
experience. Further, many of the coolest objects, like galaxies and
nebulae, can only be seen fully under low power because of their size.
size is the true key to the "power" of a telescope:
The aperture of a scope refers to the diameter
of either the objective lens of a refractor or objective mirror of a
reflector. Its ability to gather light is directly proportional to the
size of its aperture and the more light a scope can gather, the better
the image you will see. Typically, 2.4 inch (60mm) and 3.1 inch(80mm)
refractors and 4.5 inch and 6 inch reflectors are popular for most
a Telescopes Focal Ratio: The focal ratio is calculated by dividing
aperture size into its focal length. The focal length is measured from
the main lens (or mirror) to where the light converges to focus. As an
example, a scope with an aperture of 4.5 inches and focal length of 45
inches, will have a focal ratio of f10.
While a higher focal ratio does not always mean
a higher quality image, it often means as good an image for similar
cost. However, a higher focal ratio with the same size aperture means a
longer scope, which can translate into transportation woes.
Main Types Of Telescopes And There Uses:
1. The Refracting Telescope or Refractor
Refracting telescopes are the most common form of the telescope - a
long, thin tube where light passes in a straight line from the front
objective lens directly to the eyepiece at the opposite end of the tube.
* Easy to use and consistent due to the
simplicity of design.
* Good for distant terrestrial viewing
* Excellent for lunar, planetary and binary stargazing especially with
* Sealed tube protects optics and reduces image degrading air currents
* Rugged, need little or no maintenance
have small apertures, typically 3 to 5 inches
* Less suited for viewing small and faint deep sky objects such as
distant galaxies and nebulae
* Heavier, longer and bulkier than equivalent aperture reflectors and
* Limited practical usefulness
* Good-quality refractors cost more per
inch of aperture than any other kind of telescope.
The Reflecting Telescope or Reflector
telescopes use a huge
concave parabolic mirror instead of a lens to gather and focus the
light to a flat secondary mirror that in turn reflects the image out of
an opening at the side of the main tube. You look through an eyepiece
on the side of the tube up near the top.
* Easy to use and even construct
* Excellent for faint deep sky objects such as remote galaxies, nebulae
and star clusters because of their larger apertures for light gathering.
* Low in optical irregularities and deliver very bright images
* Reasonably compact and portable
* A reflector costs the least per inch of aperture compared to
refractors and catadioptrics since mirrors can be produced at less cost
* Generally, not suited for terrestrial
* Slight light loss due to secondary obstruction when compared with
* The tube is open to the air, which means dust on the optics even if
the tube is kept under wraps
* Reflectors may require a little more care and maintenance
3. Catadioptric Telescope
telescopes use a combination of mirrors and lenses to fold the optics
and form an image. Catadioptrics are the most popular type of
instrument, with the most modern design, marketed throughout the world in 3 inch and
larger apertures. There are two popular designs, the Schmidt-Cassegrain
and the Maksutov-Cassegrain.
Schmidt-Cassegrain, light enters through a thin aspheric Schmidt
correcting lens, then strikes the spherical primary mirror and is
reflected back up the tube to be intercepted by a small secondary mirror. The mirror then
reflects the light out an opening in the rear of the instrument where
the image is formed at the eyepiece.
* Most versatile type of
* Best near focus capability of any type telescope
* First-rate for deep sky observing or astrophotography with fast films
* Excellent for lunar, planetary and binary star observing plus
terrestrial viewing and photography
* Closed tube design reduces image degrading air currents
* Compact and durable
* More expensive than reflectors of equal
* Its appearance may not be suited to everybody's taste
* Slight light loss due to secondary mirror obstruction compared to
Maksutov-Cassegrain telescope design has basically the same advantages
and disadvantages as the Schmidt. It uses a thick meniscus-correcting
lens with a strong curvature and a secondary
mirror that is usually an aluminized spot on the corrector. The
Maksutov secondary mirror is typically smaller than the Schmidt's
giving it slightly better resolution for planetary observing.
Maksutov is heavier than the Schmidt and because of the thick
correcting lens, it takes a long time to reach thermal stability at
night in larger apertures. The Maksutov optical design typically is easier to make but requires
more material for the corrector lens than the Schmidt Cassegrain.