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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.
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:
Magnification =
(focal length of telescope) ÷ (focal length of eyepiece)
For example, the StarMax 102mm EQ, which has a focal
length of 1300mm, used in combination with the 25mm eye-
piece, yields a power of
1300mm ÷ 25mm = 52x
Every telescope has a useful limit of power of about 2x per
mm of aperture (about 204x for the StarMax 102mm EQ).
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), it’s 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.
Deep-sky objects, however, typically look better at medium or
low magnifications. This is because many of them are quite
faint, yet have some extent (apparent width). Deep-sky
objects will often disappear at higher magnifications, since
greater magnification inherently yields dimmer images. This is
not the case for all deep-sky objects, however. Many galaxies
are quite small, yet are somewhat bright, so higher power
may show more detail.
The best rule of thumb with eyepiece selection is to start with
a low power, wide field, and then work your way up in magni-
fication. 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.
Rotating the Diagonal
When looking at objects in different areas of the night sky, the
eyepiece may become positioned so that is uncomfortable or
impossible to look through. If the eyepiece is in an undesirable
position, the diagonal can be rotated in order to provide a
more comfortable viewing angle. First, loosen the thumb
screws on the eyepiece adapter, but make sure to hold the
diagonal in place so that it won’t fall to the ground. Also,
secure the eyepiece in the diagonal so that it won’t fall out
when rotating the diagonal. Retighten the thumb screws on
the eyepiece adapter once the diagonal has been rotated to
an appropriate position.
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 surface.
B. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional full-aperture solar filter over
the front opening of the StarMax 102mm EQ. The primary
attraction is sunspots, which change shape, appearance, and
location daily. Sunspots are directly related to magnetic activ-
ity in the Sun. Many observers like to make drawings of
sunspots to monitor how the Sun is changing from day to day.
Important Note: Do not look at the Sun with any optical
instrument without a professionally made solar filter, or
permanent eye damage could result.
C. The Planets
The planets don’t stay put like the stars, so to find them you
should refer to Sky Calendar at our website (www.tele-
scope.com), or to charts published monthly in Astronomy,
Sky & Telescope, or other astronomy magazines. Venus,
Mars, Jupiter, and Saturn are the brightest objects in the sky
after the Sun and the Moon. Your StarMax 102mm EQ 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 recommended and often needed for
detailed observations. Not all the planets are generally visible
at any one time.
JUPITER The largest planet, Jupiter, is a great subject for
observation. You can see the disk of the giant planet and
watch the ever-changing positions of its four largest moons—
Io, Callisto, Europa, and Ganymede. Higher-power eyepieces
should bring out the cloud bands on the planet’s disk.
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