I Mage O Rientation; C Alculating M Agnification - Celestron CGEM II 1100 EdgeHD Mode D'emploi

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mage RieNTaTioN
The image orientation changes depending on how the
eyepiece is inserted into the telescope. When using the star
diagonal with refractors and Schmidt-Cassegrains or Maksutovs,
the image is right-side-up, but reversed from left-to-right (i.e.,
mirror image). If inserting the eyepiece directly into the focuser
of a refractor or the visual back of the Schmidt-Cassegrain or
Maksutov (i.e., without the star diagonal), the image is upside-
down and reversed from left-to-right (i.e., inverted).
A
ctuAl imAge oRientAtion As seen
with the unAided eye
f
ocuSiNg
To focus your refractor or Newtonian telescope, simply turn the
focus knob located directly below the eyepiece holder.
The Schmidt-Cassegrain focusing mechanism controls the
primary mirror which is mounted on a ring that slides back and
forth on the primary baffle tube. The focusing knob, which
moves the primary mirror, is located on the rear cell of the
telescope to the right, or just below (on some models) the
star diagonal and eyepiece. Turn the focusing knob until the
image is sharp. If the knob will not turn, it has reached the end
of its travel on the focusing mechanism. Turn the knob in the
opposite direction until the image is sharp. Once an image is in
focus, turn the knob clockwise to focus on a closer object and
counterclockwise for a more distant object. A single turn of the
focusing knob moves the primary mirror only slightly. Therefore,
it will take many turns (about 30) to go from close (near) focus
to infinity.
c
alculaTiNg
You can change the power of your telescope just by changing
the eyepiece (ocular). To determine the magnification of your
telescope, simply divide the focal length of the telescope by
the focal length of the eyepiece used. In equation format, the
formula looks like this:
Magnification =
True (Actual) Field of View =
m
agNificaTioN
Focal Length of Telescope (mm)
Focal Length of Eyepiece (mm)
Apparent Field of Eyepiece
Magnification
Newtonian reflectors produce a right-side-up image but
the image will appear rotated based on the location of the
eyepiece holder in relation to the ground. Newtonian reflectors
are best for astronomical use where right-side-up does not
matter.
R
eveRsed fRom left to Right
s d
viewed using A tAR iAgonAl on A
s -c
RefRActoR oR chmidt AssegRAin
For astronomical viewing, out of focus star images are very
diffuse, making them difficult to see. If you turn the focus knob
too quickly, you can go right through focus without seeing the
image. To avoid this problem, your first astronomical target
should be a bright object (like the Moon or a planet) so that
the image is visible even when out of focus. Critical focusing is
best accomplished when the focusing knob is turned in such
a manner that the mirror moves against the pull of gravity.
In doing so, any mirror shift is minimized. For astronomical
observing, both visually and photographically, this is done by
turning the focus knob counterclockwise.
Note: If you wear corrective lenses (specifically glasses),
you may want to remove them when observing with an
eyepiece attached to the telescope. However, when
using a camera you should always wear corrective
lenses to ensure the sharpest possible focus. If you have
astigmatism, corrective lenses must be worn at all times.
Let's say, for example, you are using a 25mm eyepiece that
may have been supplied with your telescope. To determine
the magnification you simply divide the focal length of your
telescope (for this example we will assume your telescope has
a focal length of 1000 mm) by the focal length of the eyepiece,
25 mm. Dividing 1000 by 25 yields a magnification of 40 power.
Although the power is variable, each instrument under average
skies has a limit to the highest useful magnification. The general
rule is that 60 power can be used for every inch of aperture.
For example, the telescope above is 4 inches in diameter.
Multiplying 4 by 60 gives a maximum useful magnification of
240 power. Although this is the maximum useful magnification,
most observing is done in the range of 20 to 35 power for every
inch of aperture which is 80 to 140 times for the telescope used
in the example. You can determine the magnification for your
telescope the same way.
Note on Using High Powers – High powers are used
mainly for lunar and planetary observing where you
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