Orion SKYQUEST XT12 User Manual download pdf (Page 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.

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Orion SKYQUEST XT12 User Manual Page 15

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