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Out of collimation
Figure 19.
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 right if optics are perfectly
collimated. If circle is unsymmetrical, as in illustration on left, scope
needs collimation.
star‑testing the telescope
When it is dark, point the telescope at a bright star and accu‑
rately center it in the eyepiece's field‑of‑view. Slowly defocus
the image with the focusing knob. If the telescope is correct‑
ly collimated, the expanding disk should be a perfect circle
(Figure 19). If the image is unsymmetrical, the scope is out
of collimation. The dark shadow cast by the secondary mirror
should appear in the very center of the out‑of‑focus circle, like
the hole in a doughnut. If the "hole" appears off‑center, the
telescope is out of collimation.
If you try the star test and the bright star you have selected
is not accurately centered in the eyepiece, then the optics
will always appear out of collimation, even though they may
be perfectly aligned. It is critical to keep the star centered,
so over time you will need to make slight corrections to the
telescope's position in order to account for the sky's apparent
motion.
8. astronomical observing
For many users, the Atlas 10 EQ telescope will be a major
leap into the world of amateur astronomy. This section is
intended to get you ready for your voyages through the night
sky.
observing tips
A. Site Selection
Pick a location away from street lights and bright yard light‑
ing. Avoid viewing over rooftops and chimneys, as they often
have warm air currents rising from them, which distort the
image seen in the eyepiece. Similarly, you should not observe
through an open window from indoors. Better yet, choose
a site out‑of‑town, away from any "light pollution". You'll be
stunned at how many more stars you'll see! Most importantly,
make sure that any chosen site has a clear view of a large
portion of the sky.
B. Seeing and Transparency
Atmospheric conditions play a huge part in quality of view‑
ing. In conditions of good "seeing", star twinkling is minimal
and objects appear steady in the eyepiece. Seeing is best
14
Collimated
Figure 20.
"pan". It is a good guide to how conditions are. If you can not see
Megrez (a 3.4 mag star) then conditions are poor.
overhead, worst at the horizon. Also, seeing generally gets
better after midnight, when much of the heat absorbed by the
Earth during the day has radiated off into space. Typically,
seeing conditions will be better at sites that have an altitude
over about 3000 feet. Altitude helps because it decreases
the amount of distortion causing atmosphere you are looking
through.
A good way to judge if the seeing is good or not is to look at
bright stars about 40° above the horizon. If the stars appear to
"twinkle", the atmosphere is significantly distorting the incom‑
ing light, and views at high magnifications will not appear
sharp. If the stars appear steady and do not twinkle, seeing
conditions are probably good and higher magnifications will
be possible. Also, seeing conditions are typically poor during
the day. This is because the heat from the Sun warms the air
and causes turbulence.
Good "transparency" is especially important for observ‑
ing faint objects. It simply means the air is free of moisture,
smoke, and dust. All tend to scatter light, which reduces an
object's brightness.
One good way to tell if conditions are good is by how many
stars you can see with your naked eye. If you cannot see
stars of magnitude 3.5 or dimmer then conditions are poor.
Magnitude is a measure of how bright a star is, the brighter a
star is, the lower its magnitude will be. A good star to remem‑
ber for this is Megrez (mag. 3.4), which is the star in the "Big
Dipper" connecting 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 20).
C. Cooling the Telescope
All optical instruments need time to reach "thermal equilib‑
rium" to achieve maximum stability of the lenses and mirrors,
which is essential for peak performance. 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 temperature change,
the more time will be needed. The Atlas 10 mirror is made
of Pyrex, which is a low‑expansion material used for supe‑
rior thermal stability. The use of Pyrex reduces the amount of
Megrez connects the Big Dipper's handle to it's
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