Cooling The Telescope - Orion starBlast 4.5 EQ Instruction Manual

when much of the heat absorbed by the Earth during the day
has radiated off into space.
Especially important for observing faint objects is good "trans-
parency"—air free of moisture, smoke, and dust. All tend to scat-
ter light, which reduces an object's brightness. Transparency is
judged by the magnitude of the faintest stars you can see with
the unaided eye (6th magnitude or fainter is desirable).

cooling the telescope

All optical instruments need time to reach "thermal equilibri-
um." The bigger the instrument and the larger the temperature
change, the more time is needed. Allow at least 30 minutes for
your telescope to acclimate to the temperature outdoors.
let Your Eyes Dark‑adapt
Don't expect to go from a lighted house into the darkness of the
outdoors at night and immediately see faint nebulas, galaxies,
and star clusters—or even very many stars, for that matter. Your
eyes take about 30 minutes to reach perhaps 80% of their full
dark-adapted sensitivity. As your eyes become dark-adapted,
more stars will glimmer into view and you'll be able to see fainter
details in objects you view in your telescope.
To see what you're doing in the darkness, use a red-filtered flash-
light rather than a white light. Red light does not spoil your eyes'
dark adaptation like white light does. A flashlight with a red LED
light is ideal, or you can cover the front of a regular incandescent
flashlight with red cellophane or paper. Beware, too, that nearby
porch, streetlights, and car headlights will ruin your night vision.
Eyepiece selection
Magnification, or power, is determined by the focal length of
the telescope and the focal length of the eyepiece being used.
Therefore, by using eyepieces of different focal lengths, the
resultant magnification can be varied. It is quite common for an
observer to own five or more eyepieces to access a wide range
of magnifications. This allows the observer to choose the best
eyepiece to use depending on the object being viewed and view-
ing conditions. The StarBlast 4.5 EQ comes with two eyepieces,
which will suffice nicely to begin with.
Magnification is calculated as follows:
Telescope Focal Length (mm)
Eyepiece Focal Length (mm)
For example, the StarBlast 4.5 EQ has a focal length of 450mm,
which when used with the supplied 15mm eyepiece yields:
450 mm
15 mm
The magnification provided by the 6mm eyepiece is:
450 mm
12
= Magnification
= 30x
= 75x
6 mm
The maximum attainable magnification for a telescope is directly
related to how much light it can gather. The larger the aperture,
the more magnification is possible. In general, a figure of 60x
per inch of aperture is the maximum attainable for most tele-
scopes. Your StarBlast 4.5 EQ has an aperture of 4.5 inches, so
the maximum magnification would be about 270x. This level of
magnification assumes you have ideal conditions for observing.
Keep in mind that as you increase magnification, the brightness
of the object viewed will decrease; this is an inherent principle
of the laws of physics 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!
Start by centering the object you wish to see in the 15mm eye-
piece. Then you may want to increase the magnification to get a
closer view. If the object is off-center (i.e., it is near the edge of
the field of view) you will lose it when you increase magnification,
since the field of view will be narrower with the higher-powered
eyepiece.
To change eyepieces, first loosen the securing thumbscrews on
the focuser drawtube. Then carefully lift the eyepiece out of the
drawtube. Do not tug or pull the eyepiece to the side, as this will
knock the telescope off its target. Replace the eyepiece with the
new one by sliding it gently into the drawtube. Re-tighten the
thumbscrews, and refocus for your new magnification.
What to Expect
So what will you see with your telescope? You should be able to
see bands on Jupiter, the rings of Saturn, craters on the Moon,
the waxing and waning of Venus, and many bright deep-sky
objects. Do not expect to see color as you do in NASA photos,
since those are taken with long-exposure cameras and have
"false color" added. Our eyes are not sensitive enough to see
color in deep-sky objects except in a few of the brightest ones.
objects to observe
Now that you are all set up and ready to go, one critical decision
must be made: what to look at?
A. The Moon
With its rocky surface, the Moon is one of the easiest and most
interesting objects to view with your telescope. Lunar craters,
marias, and even mountain ranges can all be clearly seen from
a distance of 238,000 miles away! With its ever-changing phas-
es, you'll get a new view of the Moon every night. The best time
to observe our one and only natural satellite is during a partial
phase, that is, when the Moon is not full. During partial phas-
es, shadows are cast on the surface, which reveal more detail,
especially right along the border between the dark and light por-
tions of the disk (called the "terminator"). A full Moon is too bright
and devoid of surface shadows to yield a pleasing view. Make
sure to observe the Moon when it is well above the horizon to
get the sharpest images.
Use an optional Moon filter to dim the Moon when it is very
bright. It simply threads onto the bottom of the eyepieces (you
must first remove the eyepiece from the focuser to attach a fil-
ter). You'll find that the Moon filter improves viewing comfort, and
also helps to bring out subtle features on the lunar surface.