Orion SKYQUEST XT6 - Manual (Page 8)

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in the general direction of an object at least 1/4-mile away -
the top of a telephone pole, a chimney, etc. Position that
object in the center of the telescope’s eyepiece.
Now, look in the finder scope. Is the object visible? Ideally, it
will be somewhere in the field of view. If it is not, some coarse
adjustments of the two finder scope alignment thumbscrews
will be needed to get the finder scope roughly parallel to the
main tube.
Note: The image in both the finder scope and the main tele-
scope will appear upside-down (rotated 180°).This is normal
for finder scopes and reflector telescopes. (see Figure 10)
With the image in the finder scope’s field of view, use the two
alignment thumbscrews to center the object in the intersection
of the crosshairs.
By turning the alignment thumbscrews, you change the line of
sight of the finder scope. Continue making adjustments to the
alignment thumbscrews until the images in both the finder
scope and the telescope’s eyepiece are exactly centered.
Check the alignment by moving the telescope to another
object and fixing the finder scope’s crosshairs on the exact
point you want to look at. Then look through the telescope’s
eyepiece to see if that point is centered in the field of view. If it
is, the job is done. If not, make the necessary adjustments to
the finder scope alignment thumbscrews until the two images
match up.
The finder scope alignment needs to be checked before every
observing session. This can easily be done at night, before
viewing through the telescope. Choose any bright star or plan-
et, center the object in the telescope eyepiece, and then
adjust the finder scope alignment thumbscrews until the star
or planet is also centered on the finder’s crosshairs. The find-
er scope is an invaluable tool for locating objects in the night
sky; its usage for this purpose will be discussed later, in detail.
Focusing the Finder Scope
If, when looking through the finder scope, the images appear
somewhat out of focus, you will need to refocus the finder
scope for your eyes. Loosen the lock ring located behind the
objective lens cell on the body of the finder scope (see Figure
6a). Back the lock ring off by a few turns, for now. Refocus the
finder scope on a distant object by threading the objective
lens cell in or out on the finder scope body. Precise focusing
will be achieved by focusing the finder scope on a bright star.
Once the image appears sharp, retighten the lock ring behind
the objective lens cell. The finder scope’s focus should not
need to be adjusted again.
Aiming/Pointing the Telescope
Now that the finder scope is aligned, the telescope can be
quickly and accurately pointed at anything you wish to
observe. The finder scope has a much wider field of view than
the telescope’s eyepiece, and therefore it is much easier to
first center an object in the finder scope. Then, if the finder
scope is accurately aligned, the object will also be centered in
the telescope’s field of view.
Start by once again moving the telescope until it is pointed in
the general direction of the object you want to see. Some
observers find it convenient to sight along the tube to do this.
Now, look in the finder scope. If your general aim is accurate,
the object should appear somewhere in the finder scope.
Make small adjustments to the telescope’s position until the
object is centered on the finder’s crosshairs. Now, look in the
telescope’s eyepiece and enjoy the view!
Magnification
Once the object you want to view is well-centered in the
25mm eyepiece, you may want to increase the magnification
to get a closer view. Loosen the thumbscrew(s) on the focuser
drawtube and remove the eyepiece. Place it in the eyepiece
rack, if you wish. Insert the 10mm eyepiece in the focuser then
tighten the thumbscrew(s). If you were careful not to bump the
telescope, the object should still be centered within the field of
view. Notice that the object being viewed is now larger, but
somewhat dimmer.
The SkyQuest is designed to accept any eyepiece with a bar-
rel diameter of 1.25". The XT8 can also accept 2" eyepieces.
Magnification, or power, is determined by the focal length of
the telescope and the focal length of the eyepiece. Therefore,
by using eyepieces of different focal lengths, the resultant
magnification can be varied.
Magnification is calculated as follows:
Telescope Focal Length (mm)
Magnification=
Eyepiece Focal Length (mm)
The 6” and 8” SkyQuest Dobsonians both have a focal length
of 1200mm. So, the magnification with the supplied 25mm eye-
piece is:
Naked-eye view
View through finder scope and telescope
Figure 10. The view through a standard finder scope and
reflector telescope is upside down. This is true for the SkyQuest
and its finder scope as well.