15
TELESCOPE BASICS
Focusing the Telescope
To focus your telescope, begin by putting the eyepiece in the eyepiece holder of the focuser. When doing
astronomical viewing, you’ll find that out of focus star images are very diffuse and difficult to see. Therefore, choose
a bright object, like the moon or a planet for your first astronomical target. This way, the image will be visible even
when out of focus. Turn the focus knob until the object’s image becomes sharp. If you’re focusing on a star, its
image should, as closely as possible, resemble a pinpoint. If you’re focusing on the moon or a planet, turn the focus
knob until the image is sharp.
Pointing the Telescope
To aim your telescope, first locate a bright star near the object you are trying to find. You can then use your telescope
tube to sight with, helping to zero in on the object you wish to view. This can be done much as you might sight down
the barrel of a gun when lining up a shot. The idea is to use the line of the telescope tube to assist you in creating a
visual line between your eye and the object you want to view.
Once the star is aligned with the edge of the telescope
tube, look inside the eyepiece and gently move the tube up and down and from side to side until you see the object in
the field of view. Use of an optional finderscope makes locating objects for viewing much easier.
Calculating Magnification
You can change the viewing power of your
Celestron Star Hopper
®
telescope just by changing the eyepiece
(ocular). There are various optional eyepieces shown in the Optional Accessories section of this manual on pages 24
and 25. 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:
Focal Length of Telescope (mm)
Magnification =
––––––
Focal Length of Eyepiece (mm)
To determine the magnification using the standard 25mm eyepiece, simply divide the focal length of your 6” or 8”
Star Hopper
®
telescope (1220mm) by the focal length of the eyepiece (25mm). Dividing 1220mm by 25 yields a
magnification of 49 power. Although the power is variable, each telescope, used under average skies, has a limit to
its highest useful magnification. The general rule is that 60 power is the maximum that can be used for every inch of
aperture, although seeing condition rarely allow this. For example, the
Star Hopper
®
8
is 8" in diameter.
Multiplying 8 by 60 gives a maximum useful magnification of 480 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 90 to 158
for the
Star Hopper
®
4
½
,
120 to 210 for the
Star Hopper
®
6
and 160 to 280 times for the
Star Hopper
®
8
.
Determining Field of View
Determining the field of view is important if you want to get an idea of the angular size of the object you are
observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece
manufacturer) by the magnification. In equation format, the formula looks like this:
Apparent Field of Eyepiece
True Field =
Magnification
To Next Page
Loading...
