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)
Eyepiece Focal Length (mm) = Magnification
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
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
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
Transporting the Telescope
Even though it is a
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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