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Celestron's Frequently
Asked Questions
Telescope Questions
Answers
Q: How far can I see with a telescope?
A: Since the distance of a celestial
object generally corresponds to its brightness, the telescope with the
largest aperture (size
of the main mirror or lens) will not only allow you to see the faintest
objects but also the most distant objects. For example, through a 60mm refracting telescope you can see the bright center of
the Andromeda galaxy which is more than 2 million light years away. With
an 8" (200mm) telescope or larger, you can see the spiral arms of
the much fainter Whirlpool galaxy, which is 35 million light years away!
When using a telescope for daytime, terrestrial observing, the distance
you can see is limited by the condition of the atmosphere through which
you are viewing. High amounts of moisture in the air or heat waves radiating
from the ground will give you a blurry image over great distances.
Q: How do you determine the power of a telescope?
A: The magnifying power
of a telescope will change depending on the focal length
of the eyepiece you are using (see question on determining
a telescope's magnification below). A more appropriate
question may be to ask how much light-gathering power does
a telescope have. Light gathering power is a telescope's
ability to see faint, distant objects (see question above) and is solely determined by the aperture of the telescope's
main mirror or lens. The larger the aperture,
the more light-gathering power a telescope has. Remember
it's the entire surface area of the telescope's main mirror
or lens that is collecting the light; therefore every time
a telescope's aperture is
doubled, the light-gathering power is increased by a factor
of 4 times!
Q: How do you determine
a telescope’s magnification?
A: The magnification
of a telescope changes as the eyepiece is changed. Magnification
can be calculated by dividing the focal length of your telescope
by the focal length of the eyepiece.
Always start with your lowest magnification (longest focal length) eyepiece and work upward from there. A
2x Barlow lens will double the magnification of
whatever eyepiece you use with it. For example: using a telescope
with a 900mm focal length with a 20mm
eyepiece will give you 45x magnification.
Using the same telescope and eyepiece with a 2x Barlow lens
will give 90x magnification. This would be the same magnification as a 900mm telescope with a 10mm eyepiece.
Q: How can I clean
the corrector plate on my Schmidt-Cassegrain telescope?
A: The outside of the corrector plate can be
cleaned using a solution of 60% distilled water and 40% isopropyl
alcohol with one drop of clear liquid dish soap per quart
of solution. The solution is applied to a soft tissue or
cotton ball and is carefully rubbed onto the corrector plate
using radial strokes from the secondary mirror housing outward.
We do not recommend removing the corrector plate. The corrector
plate is optically matched to the mirrors in alignment and
in rotation. If the inside of the corrector plate or mirrors
becomes dirty, call Celestron and arrange to send your telescope
in for a thorough cleaning. Celestron offers complete cleaning
and collimating services. Contact the Technical Service Department
at (310) 328-9560.
Q: Where can I find a replacement battery for my 8 x 50 illuminated finderscope?
A: The 8x50 Polaris finderscope used a PX-14
mercury battery. Due to EA disposal laws, mercury batteries
are no longer legal to produce in the United States. Unfortunately,
no battery manufacturer has made a replacement 2.7V battery
in this size. PX-14 batteries may still be available through
mail order or internet battery retailers.
Q: Everything I
see through my refractor is an inverted image. How can
I correct the image?
A: To correct an inverted image, you will need a
90° star diagonal. When
a 90° star diagonal is used,
the mirror flips the image over giving a right side up but
reversed left to right image. You can achieve a fully corrected
image using an erect image prism diagonal. Contact a Celestron dealer to order either one of these accessories, call
Celestron Customer Service at (310) 328-9560, or visit our dealer
page to find a Celestron dealer near you.
Q: Why can't I see anything
in my telescope when I have the moon centered in the
cross hairs of my finderscope?
A: The most likely cause of the problem is that your
finderscope is not aligned with the main optics. To align
your finderscope, take your scope outside in the daylight
and find an object at least a half mile away as far away
as possible (a street sign, telephone pole, radio tower,
mountain top, etc.). Center this object in your main telescope
using your lowest power eyepiece. Now look through your finderscope.
Using the three adjustment screws that secure the finderscope
into its bracket, tighten or loosen them as needed to bring
the cross hairs onto the same target as is centered in your
main telescope. Your scope is now ready to be aimed at any
object in the sky and it will easily be located through the
main optics of your scope.
Q: I have a 60mm
refractor with a focal length of 900mm. Why can't I get
a clear image when I try to use my 2x Barlow lens with
my 6mm eyepiece?
A: All telescopes have a maximum magnification of 60x per inch
of aperture (under ideal conditions).
Your telescope would reach this limit at about 140x magnification.
The combination you are using gives 300x magnification (see
formula above). Exceeding the maximum usable limit will cause
the image to degrade, becoming dark and washed out. The Earth's
atmosphere also plays an important part in limiting the maximum magnification you can use. Instabilities
in the atmosphere such as heat radiating from the ground
and surrounding buildings, high altitude winds, and other
weather conditions can cause your image to blur. This also
explains why bright stars appear to twinkle. The best time
to use high magnification is on nights when
the stars do not appear to twinkle very much.
Q: Why don’t
the images I see through my telescope look the same as
photos I see taken with the same type of telescope?
A: Many pictures you see in magazines and catalogs
are time exposures. The camera shutter is kept open for several
minutes while the telescope tracks the object across the
sky. This allows the film to record fainter detail and colors
that can not be seen with the naked eye. In order to get
similar results with your telescope, you need a camera
adapter for a 35mm camera and a clock motor.
Q: What is the difference between
an equatorial mounted telescope and an Altazimuth mounted
telescope?
A: A mount is said to be "equatorial" if
one of its axes can be made parallel to the Earth's axis
of rotation (called the Celestial Pole). This is essential
if you want to track an object over a long period of time
as it moves across the sky. With an equatorial mount the
motion of the sky can be cancelled out by simply turning
its axis at the same rate as the Earth's rotation, but in
the opposite direction. Equatorial mounts are necessary for
long exposure astrophotography and for using setting
circles to locate objects. Altazimuth (short for Altitude/Azimuth)
mounts are the simplest type of mount. This type of mount
moves in two directions, altitude (up and down) and azimuth
(side-to-side). Due to their ease of use, Altazimuth mounts
are suited both for terrestrial viewing as well as astronomical
observing. |
