Orion XT12 - Manual (Page 15)

15
Aiming/Pointing the Telescope
With the finder scope 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 tele-
scope’s eyepiece, and therefore it is much easier to find and
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 accu-
rate, the object should appear somewhere in the field of view.
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!
Some objects are too faint to be seen with the small aperture
of the finder scope. In those cases, you will need to interpo-
late your position using stars as guideposts. A star map will
help you in doing so.
Magnification
Now that the object you want to view is centered in the 25mm
eyepiece, you may want to increase the magnification to get a
closer view. Loosen the thumbscrew 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. If you were careful not to bump the telescope,
the object should still be visible in the field of view. Notice that
the object being viewed is now larger, but somewhat dimmer.
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 SkyQuest XT12 IntelliScope has a focal length of
1500mm. So, the magnification with the supplied 25mm eye-
piece is:
1500 mm
= 60x
25 mm
The magnification provided by the 10mm eyepiece is:
1500 mm
= 150x
10 mm
The maximum attainable magnification for a telescope is
directly related to how much light its optics can collect. A tele-
scope with more light-collecting area, or aperture, can yield
higher magnifications than a smaller-aperture telescope. The
maximum practical magnification for any telescope, regard-
less of optical design, is about 60x per inch of aperture. This
translates to about 720x for the SkyQuest XT12 IntelliScope.
Of course, such magnification will only yield reasonable imag-
es if atmospheric conditions are favorable.
More typically, useful magnifications will be limited to 200x
or less, regardless of aperture. This is because the Earth’s
atmosphere distorts light as it passes through. On nights of
good “seeing,” the atmosphere will be still and will yield the
least amount of distortion. On nights of poor seeing, the
atmosphere will be turbulent, which means different densities
of air are rapidly mixing. This causes significant distortion of
the incoming light, which prevents sharp views at high mag-
nifications.
Keep in mind that as magnification is increased, the bright-
ness of the object being viewed will decrease; this is an
inherent principle of the physics of optics and cannot be
avoided. If magnification is doubled, an image appears four
times dimmer. If magnification is tripled, image brightness is
reduced by a factor of nine!
Use of 2" Eyepieces
The SkyQuest XT12 IntelliScope is designed to accept eye-
pieces with a barrel diameter of either 1.25" or 2". At low
magnifications, 2" eyepieces can provide a wider field of view
than standard 1.25" eyepieces. A wider field can be desirable
for viewing extended deep-sky objects that are too large to fit
within a narrower field of view.
To use 2" eyepieces, simply loosen the two large thumbscrews
on the 2" adapter (Figure 20). Once these thumbscrews are
loosened, the 1.25" adapter comes off, exposing the 2" diam-
eter focuser drawtube. Now, insert a 2" eyepiece into the
drawtube and secure with the two thumbscrews loosened
previously, and you’re ready to observe.
Tube Balance
SkyQuest IntelliScope Dobsonians are designed to balance
with standard supplied accessories, such as an eyepiece and
a finder scope. But what if you want to use a larger finder
scope or a heavier eyepiece? Traditional Dobsonian designs
require the user to compensate by adding weight to the oppo-
site end of the telescope tube. Such counterweighting systems
can be expensive and unwieldy. The CorrecTension system of
the SkyQuest IntelliScope Dobsonians, however, solves the
finicky balance problem. The brake pads press against the
altitude bearings on the optical tube and increase the fric-
tion. With CorrecTension, the added weight of front-end loads
will not adversely affect the balance of the telescope. Simply
tighten the tensioning knob to balance any extra load.
Transporting the Telescope
Even though it is a larger-aperture instrument, transporting
the SkyQuest XT12 IntelliScope is relatively easy. The opti-
cal tube uncouples from the base and each component can
be carried separately. The base even has a handle for your
convenience.
To remove the optical tube from the base, simply unthread
Note: If you choose to thread the knobs back into the
altitude bearings after removing the optical tube from the
base, be careful not to bend the knobs when transport-
ing the telescope.