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Thumbscrew
Dovetail shoe
Figure 7. To install the finder scope, slide the bracket foot forward
in the dovetail shoe, then tighten the thumbscrew on the shoe.
Lock ring
Eyepiece
Drawtube
lock
Diagonal
Figure 8. Install a diagonal (90-degree diagonal shown) in the
focuser collar, then install an eyepiece in the diagonal.
Note that both the azimuth and altitude axes have a knurled
"micro-motion" knob (Figure 11). Turning these knobs provides
a controlled micro adjustment, which can be helpful for center-
ing a target in the telescope's eyepiece.
Eyepiece Selection
Magnification, or power, is determined by the focal length of
the telescope and the focal length of the eyepiece being used.
Therefore, by using eyepieces of different focal lengths, the
resultant magnification can be varied. It is quite common for an
observer to own five or more eyepieces to access a wide range
of magnifications. This allows the observer to choose the best
6
Objective
lens cell
Focus collar
Focus wheel
Figure 9. Two 1.25" diagonals are included with the VersaGo
GX 80: a 90-degree mirror star diagonal that's recommended for
astronomical observing, and a 45-degree correct-image prism
diagonal that is recommended for daytime terrestrial use.
eyepiece to use depending on the object being viewed and
viewing conditions. Your VersaGo GX 80 refractor comes with
25mm and 10mm Sirius Plössl eyepieces, which will suffice
nicely to begin with. You can purchase additional eyepieces
later if you wish to have more magnification options.
Magnification is calculated as follows:
Telescope Focal Length (mm) / Eyepiece Focal Length
(mm) = Magnification
For example, the VersaGo GX 80 has a focal length of 400mm,
which when used with the supplied 25mm eyepiece yields::
400mm / 25mm = 16x
The magnification provided by the 10mm eyepiece is:
400mm / 10mm = 40x
The maximum attainable magnification for a telescope is
directly related to how much light it can gather. The larger the
aperture, the more magnification is possible. In general, a
figure of 50x per inch of aperture is the maximum attainable
for most telescopes. Going beyond that will yield simply
blurry, unsatisfactory views. Your VersaGo GX 80 telescope
has an aperture of 80mm, or 3.1 inches, so the maximum
magnification would be about 155x (3.1 x 50). This level of
magnification assumes you have ideal atmospheric conditions
for observing (which is seldom the case).
Keep in mind that as you increase magnification, the bright-
ness of the object viewed will decrease; this is an inherent
principle of the laws of physics and cannot be avoided. If mag-
nification is doubled, an image appears four times dimmer. If
magnification is tripled, image brightness is reduced by a fac-
tor of nine!
So start by using the 25mm eyepiece, then try switching to the
10mm eyepiece later if you want to boost the magnification.
90° diagonal
45° correct-image
diagonal
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