Orion SKYQUEST XT10 - Manual (Page 15)

15
note about the Collimatable 2" Crayford Focuser
(Xt8, Xt10 only)
The 2" focuser of the SkyQuest XT8 and XT10 can be col-
limated using three pairs of push-pull screws located at the
base of the focuser (Figure 13a). The focuser was collimated
at the factory however, and should never need to be adjusted.
Focuser collimation is only required under very rare circum-
stances but has been made available for this telescope should
such a need arise.
5. astronomical observing
SkyQuest IntelliScope Dobsonians provide prodigious capa-
bility 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 observing tips and briefly summa-
rize what you can expect to see.
a. 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-dark 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. For observing faint deep-
sky objects, choose a Moonless night. Use of a light-pollution
filter can mitigate the effects of background sky brightness,
enhancing the view of faint objects.
B. 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 better
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 (see
Figure 25).
C. 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 out-
door temperature. The bigger the instrument and the larger
the temperature change, the more time will be needed.
Allow at least 30 minutes for your SkyQuest IntelliScope to
equilibrate. If the temperature difference between indoors and
outdoors is more than 40°, allow an hour or more. In the win-
ter, storing the telescope outdoors in a shed or garage greatly
reduces the amount of time needed for the optics to stabilize.
It also is a good idea to keep the scope covered until the Sun
sets so the tube does not heat greatly above the temperature
of the outside air.
Figure 24. A star test will determine if a telescope’s optics are
properly collimated. An unfocused view of a bright star through
the eyepiece should appear as illustrated on the right if the optics
are perfectly collimated. If the circle is unsymmetrical, as in the
illustration on the left, the scope needs collimation.
Out of collimation Collimated
1.9
1.9
1.7
4.9
2.4 3.4
2.5
2.4
Figure 25. Megrez connects the Big Dipper’s handle to it's “pan”.
It is a good guide to judging the “seeing” conditions. If you cannot
see Megrez (a 3.4-magnitude star) then seeing is poor.