To see what you’re doing in the darkness, use a red-filtered
flashlight 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 and streetlights and car head-
lights will ruin your night vision.
Eyepiece selection
By using eyepieces of varying focal lengths, it is possible to
attain many magnifications with your telescope. The Space-
Probe 3 Altaz comes with two Explorer II eyepieces, a 25mm
and a 10mm. These give magnifications of 28x and 70x
respectively. Other eyepieces can be used to achieve higher
or lower powers. It is quite common for an observer to own
five or more eyepieces to access a wide range of magnifica-
tions. This allows the observer to choose the best eyepiece to
use depending on the object being viewed.
To calculate the magnification, or power, of a telescope and
eyepiece combination, simply divide the focal length of the
telescope by the focal length of the eyepiece:
Telescope Focal Length (mm)
Magnification =
Eyepiece Focal Length (mm)
For example, the SpaceProbe 3 Altaz, which has a focal
length of 700mm, used in combination with the 25mm eye-
piece, yields a magnification of:
700mm
= 28x
25mm
Every telescope has a useful limit of power of about 2x per
mm of aperture (about 152x for the SpaceProbe 3 Altaz.)
Claims of higher power by some telescope manufacturers are
a misleading advertising gimmick and should be dismissed.
Keep in mind that at higher powers, an image will always be
dimmer and less sharp (this is a fundamental law of optics.)
The steadiness of the air (the “seeing”) will also limit how
much magnification an image can tolerate.
Whatever you choose to view, always start by inserting your
lowest-power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of
view, which shows a larger area of sky in the eyepiece. This
makes acquiring and centering an object much easier. If you
try to find and center objects with high power (narrow field of
view), its like trying to find a needle in a haystack!
Once you’ve centered the object in the eyepiece, you can
switch to higher magnification (shorter focal length eyepiece),
if you wish. This is especially recommended for small and
bright objects, like planets and double stars. The Moon also
takes higher magnifications well.
The best rule of thumb with eyepiece selection is to start with
a low power, wide-field eyepiece, and then work your way up
in magnification. 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.
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 cam-
eras 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.
Remember that you are seeing these objects using your own
telescope with your own eyes! The object you see in your eye-
piece is in real-time, and not some conveniently provided
image from an expensive space probe. Each session with
your telescope will be a learning experience. Each time you
work with your telescope it will get easier to use, and stellar
objects will become easier to find. Take it from us, there is big
difference between looking at a well-made full-color NASA
image of a deep-sky object in a lit room during the daytime,
and seeing that same object in your telescope at night. One
can merely be a pretty image someone gave to you. The other
is an experience you will never forget!
objects to observe
Now that you are all set up and ready to go, one critical deci-
sion must be made: what to look at?
A. The Moon
With its rocky surface, the Moon is one of the easiest and most
interesting targets 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
phases, you’ll get a new view of the Moon every night. The
best time to observe our one and only natural satellite is dur-
ing a partial phase, that is, when the Moon is NOT full. During
partial phases, shadows are cast on the surface, which reveal
more detail, especially right along the border between the dark
and light portions 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 sur-
face.
B. The Planets
The planets don’t stay put like the stars, so to find them you
should refer to Sky Calendar at our website (telescope.com),
or to charts published monthly in Astronomy, Sky & Tele scope,
or other astronomy magazines. Venus, Mars, Jupiter, and
Saturn are the brightest objects in the sky after the Sun and
the Moon. Your SpaceProbe 3 Altaz is capable of showing you
these planets in some detail. Other planets may be visible but
will likely appear star-like. Because planets are quite small in
apparent size, optional higher-power eyepieces are recom-
mended and often needed for detailed observations. Not all
the planets are generally visible at any one time.
7
