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The SkyQuest XTg is designed to accept eyepieces 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.
transporting the telescope
The SkyQuest XTg Dobs have been designed to be easy to
transport. The optical tube uncouples from the base by loos-
ening a single hand knob, and the tube and base can be car-
ried separately. The base has three carry handles for your
convenience.
Before transporting the telescope, remove the EZ Finder II
(with bracket) and any eyepieces from the optical tube. The
eyepiece rack can also be removed from the base, if you wish.
This will prevent these accessories from being damaged dur-
ing transport. These items can be placed in optional acces-
sory cases.
To remove the optical tube from the base, first orient the tube
so it is horizontal. Then unthread the tube connecting knob
(see Figure 19) until it disengages from the metal dovetail
trunnion on the base. You needn't unthread it completely from
the telescope side bearing. Grasp the rear end ring of the
tube with one hand and cradle underneath the front portion
of tube with your other arm (see Figure 18). Then, using both
hands, carefully lift the tube upward and off the base.
Note: If you choose to thread the knobs back into the alti-
tude bearings after removing the optical tube from the
base, be careful not to bend the knobs when transporting
the telescope.
When putting the XTg into a vehicle, common sense prevails.
It is especially important that the optical tube does not get
knocked around; this can cause the optics to become mis-
aligned, and could dent the tube.
We recommend transporting (and storing) the tube assembly
in the optional padded case for proper protection.
6. astronomical observing
The SkyQuest XTg GoTo Dobsonian provides prodigious
capability for observing the many wonders of the heavens,
from the major planets to deep-space nebulas and galaxies.
In this section we give you some astronomical observing tips
and briefly summarize what you can expect to see.
selecting an observing site
Since most astronomical objects are faint, observing them
from dark skies will give you the best views. While some
objects, such as the planets and Moon, are bright enough
to see clearly even from light-polluted city skies, for nebulas,
galaxies, and most star clusters, the less ambient light there
is to reduce contrast, the better.
When it isn't possible or convenient to get out of town to a pitch-
black observing location, try to set up in a spot that is removed
from street and building lights and that has a clear view of a
large portion of the sky. Avoid pointing the telescope above
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buildings, if possible, since they radiate heat which degrades
images. For observing faint deep sky objects, choose a moon-
less night. Using the optional light shroud will be a necessity
(see below). Also, use of a light-pollution filter, like the Orion
SkyGlow Broadband filter, can mitigate the effects of back-
ground sky brightness, enhancing the view of faint objects.
seeing and transparency
Atmospheric conditions play a huge part in quality of viewing.
Light from stars and other celestial objects must travel through
miles of Earth's atmosphere to reach our eyes. The air in the
atmosphere will refract and bend the light. Atmospheric tur-
bulence will worsen the effects of refraction, which can cause
the image you see in your telescope to be unstable. The
steadiness of the atmosphere is called "seeing."
In conditions of good "seeing," star twinkling is minimal and
objects appear steady in the eyepiece. Seeing is best over-
head, worst at the horizon. Also, seeing generally gets bet-
ter later in the evening as much of the heat absorbed by the
Earth during the day has radiated off into space. In condi-
tions of bad seeing, stars will twinkle and objects will appear
unsteady and blurry in the telescope.
"Transparency" is the clarity of the atmosphere, which can
be adversely affected by the presence of moisture, smoke,
and dust. All tend to scatter light, which reduces an object's
brightness. Good transparency is desirable for astronomical
observing, especially for viewing faint objects.
One good measure of transparency is by how many stars
you can see with your unaided eyes. If you cannot see
stars of magnitude 3.5 or dimmer then transparency is poor.
Magnitude is a measure of how bright a star is. The brighter
a star, the lower its magnitude. A good star to remember for
this is Megrez (magnitude 3.4), which is the star in the Big
Dipper that connects the handle to the "dipper." If you cannot
see Megrez, then you have fog, haze, clouds, smog, light pol-
lution or other conditions that are hindering your viewing.
cooling the telescope
All optical instruments need time to reach thermal equilibrium
to achieve maximum stability of the lenses and mirrors, which
is essential for peak performance. Images will be unstable if
the optics are not in equilibrium with the outdoor temperature.
When moved from a warm indoor location outside to cooler air
(or vice-versa), a telescope needs time to cool to the outdoor
temperature. The bigger the instrument and the larger the tem-
perature change, the more time will be needed. Allow at least
30 minutes or so to equilibrate. If the temperature difference
between indoors and outdoors is more than 40°, it will likely
take longer. In the winter, storing the telescope outdoors in a
shed or garage greatly reduces the amount of time needed
for the optics to stabilize. Also, after setting up outdoors, it is a
good idea to keep the telescope covered until the Sun sets so
the tube does not heat greatly above the temperature of the air.
let Your Eyes Dark-adapt
Do not expect to go from a lighted house into the darkness
of the outdoors at night and immediately see faint nebulas,
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