Advertisement
and bright objects, like planets and double stars. The Moon also
takes higher magnifications well.
Deep-sky objects, however, typically look better at medium or
low magnifications. This is because many of them are quite faint,
yet have some extent (apparent width). Deep-sky objects will
often disappear at higher magnifications, since greater magnifi-
cation inherently yields dimmer images. This is not the case for
all deep-sky objects, however. Many galaxies are quite small, yet
are somewhat bright, so higher power may show more detail.
The best rule of thumb with eyepiece selection is to start with a
low power, wide field, and then work your way up in magnifica-
tion. If the object looks better, try an even higher magnification. If
the object looks worse, then back off the magnification a little by
using a lower-power eyepiece.
Extra Accessories with the SkyQuest XT8
Limited Edition!
The #8967 SkyQuest XT8 Limited Edition Dobsonian
comes with extra accessories that are not included with the
standard SkyQuest XT Dobsonians:
• Instead of a 1.25" 25mm Plossl eyepiece, the
Special Edition includes a 2" 25mm Wide-Angle
(WA) eyepiece (BB2 in Figure 1B), which boasts
a 70-degree field of view. Its barrel is threaded to
accept Orion 2" filters.
• A 10mm Plossl eyepiece, 1.25" (BB1), for higher-
power views. Its barrel is threaded to accept Orion
1.25" filters.
• A 2x Barlow lens, 1.25" (BB3), which doubles the
magnifying power of any 1.25" eyepiece it is used
with. The Barlow lens is inserted into the focuser,
and the 1.25" eyepiece is then secured in the
Barlow lens.
These terrific accessories will increase the versatility of
your telescope, giving you more options for enhancing your
observing experience!
Magnification Limits
Every telescope has a theoretical magnification limit of about
2x per millimeter of aperture. This comes to 410x for the
SkyQuest XT8 Classic and 304x for the SkyQuest XT6 Classic
for example. But maximum magnifications are achieved only
under the most ideal viewing conditions at the best observ-
ing sites. Most of the time, the highest practical magnification
will be 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 densi-
ties of air are rapidly mixing. This causes significant distortion
of the incoming light, which prevents sharp views at high mag-
nifications.
Some telescope manufacturers will use misleading claims of
excess magnification, such as "See distant galaxies at 640X!"
While such magnifications are technically possible, the actual
image at that magnification would be an indistinct blur. Low
10
and moderate magnifications are typically what give the best
views. A small, but bright and detailed image is always better
than a dim, unclear, over-magnified one.
Tube Balance
Dobsonians are designed to balance with standard supplied
accessories, such as an eyepiece and red dot finder scope.
But what if you want to use a larger finder scope or a heavier
eyepiece? The telescope will no longer be properly balanced,
and will not hold its position properly. This makes the telescope
difficult to use, since it is critical that it hold its position (when
not purposefully moved) to keep objects centered in the field
of vision.
Traditional Dobsonian designs expect the user to compen-
sate for heavier accessories by adding weight to the opposite
end of the telescope tube. Such counterweighting systems
can be expensive and unwieldy. The CorrecTension Friction
Optimization system of the SkyQuest XT Classic Dobsonians,
however, solves the finicky balance problem. The spring coils
pull the tube down onto the base, thereby increasing the fric-
tion on the altitude bearing pads. With CorrecTension, the
added weight of small front-end loads will not adversely affect
the balance of the telescope.
If you install an array of heavier accessories onto your
SkyQuest's optical tube, you may need at some point to coun-
terbalance the telescope with a counterweight system.
Carrying the Telescope
Because the springs of the CorrecTension system hold the opti-
cal tube captive on the base, the entire telescope can be car-
ried as one unit. This requires some caution, however. If the tele-
scope is lifted improperly, the front of the tube could swing down
and hit the ground.
First, point the optical tube straight up (vertical). Grasp the han-
dle on the front of the base with one hand while supporting the
telescope tube vertically with the other. Now, lift the telescope
from the handle. Once the telescope is in the horizontal position,
you can carry the entire unit with one hand.
If you wish to carry the optical tube and base separately, simply
disengage the CorrecTension springs by unhooking them from
the posts on the base, using the pull loops. The springs remain
captive on the telescope side bearings. Now the base and tube
are disengaged and can be transported separately.
Note: The SkyQuest XT Classic may be too heavy for some
users to lift and carry as one unit. Do not strain yourself! If
the load seems too heavy, disengage the springs and carry
the base and tube separately. Because of its bulk and weight,
we do not recommend carrying the XT10 model as one unit.
Remove the XT10 optical tube from the base and carry them
separately.
When putting the telescope into a vehicle, common sense pre-
vails. It is especially important that the optical tube does not
knock around; this can cause the optics to become misaligned,
and could dent the tube. We recommend transporting and stor-
ing the tube assembly in a padded case for proper protection.
Advertisement
