6
3. Retighten the counterweight lock knob. The telescope is
now balanced on the R.A. axis.
4. To balance the telescope on the Dec. axis, first tighten
the R.A. lock knob, with the counterweight shaft still in the
horizontal position.
5. With one hand on the telescope optical tube, loosen the
Dec. lock knob (Figure 3c). The telescope should now be
able to rotate freely about the Dec. axis. Loosen the tube
ring clamps a few turns, until you can slide the telescope
tube forward and back inside the rings (this can be aided
by using a slight twisting motion on the optical tube while
you push or pull on it) (Figure 3d).
6. Position the telescope in the mounting rings so it remains
horizontal when you carefully let go with both hands. This
is the balance point for the optical tube with respect to the
Dec. axis (Figure 3e).
7. Retighten the tube ring clamps.
The telescope is now balanced on both axes. Now when you
loosen the lock knob on one or both axes and manually point
the telescope, it should move without resistance and should
not drift from where you point it.
4. Aligning the Finder-Scope
A finder scope has a wide field of view to facilitate the loca-
tion of objects for subsequent viewing through the main tele-
scope, which has a much narrower field of view. The finder
scope and the main telescope must be aligned so they point
to exactly the same spot in the sky.
Alignment is easiest to do in daylight hours. First, insert the
lowest-power (25mm) eyepiece into the star diagonal. Then
loosen the R.A. and Dec. lock knobs so the telescope can be
moved freely.
Point the main telescope at a discrete object such as the top
of a telephone pole or a street sign that is at least a quarter-
mile away. Move the telescope so the target object appears
in the very center of the field of view when you look into the
eyepiece. Now tighten the R.A. and Dec. lock knobs. Use the
slow-motion control knobs to re-center the object in the field
of view, if it moved off-center when you tightened the lock
knobs.
Now look through the finder scope. Is the object centered in
the finder scope’s field of view, (i.e., at the intersection of the
crosshairs)? If not, hopefully it will be visible somewhere in
the field of view, so that only fine adjustment of the two finder
scope alignment thumb screws will be needed to center it
on the crosshairs. Otherwise you’ll have to make coarser
adjustments to the alignment screws to redirect the aim of
the finder scope.
Note: The image seen through the finder scope appears
upside down. This is normal for astronomical finder
scopes. The image through the telescope will be inverted
left-to-right, which it normal for telescopes that utilize a
star diagonal.
Once the target object is centered on the crosshairs of the
finder scope, look again in the main telescope’s eyepiece
and see if it is still centered there as well. If it isn’t, repeat the
entire process, making sure not to move the main telescope
while adjusting the alignment of the finder scope.
The finder scope is now aligned and ready to be used for
an observing session. The finder scope and bracket can
be removed from the dovetail slot for storage, and then re-
installed without changing the finder scope’s alignment.
Focusing the Finder Scope
If, when looking through the finder scope, the images appear
somewhat out of focus, you will need to refocus the finder
scope for your eyes. Loosen the lock ring located behind the
objective lens cell on the body of the finder scope (Figure
2a). Back the lock ring off by a few turns, for now. Refocus
the finder scope on a distant object by threading the objec-
tive lens cell in or out on the finder scope body. Precise
focusing will be achieved by focusing the finder scope on a
bright star. Once the image appears sharp, retighten the lock
ring behind the objective lens cell. The finder scope’s focus
should not need to be adjusted again.
5. Setting Up and Using the
Equatorial Mount
When you look at the night sky, you no doubt have noticed
that the stars appear to move slowly from east to west over
time. That apparent motion is caused by the Earth’s rota-
tion (from west to east). An equatorial mount (Figure 4) is
designed to compensate for that motion, allowing you to
easily “track” the movement of astronomical objects, thereby
keeping them from drifting out of the telescope’s field of view
while you’re observing.
This is accomplished by slowly rotating the telescope on its
right ascension (polar) axis, using only the R.A. slow-motion
cable. But first the R.A. axis of the mount must be aligned
with the Earth’s rotational (polar) axis—a process called
polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar
alignment is achieved by pointing the mount’s R.A. axis
at the North Star, or Polaris. It lies within 1 degree of the
north celestial pole (NCP), which is an extension of the
Earth’s rotational axis out into space. Stars in the Northern
Hemisphere appear to revolve around Polaris.
To find Polaris in the sky, look north and locate the pattern
of the Big Dipper (Figure 5). The two stars at the end of the
“bowl” of the Big Dipper point right to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to
have a bright star so near the south celestial pole (SCP). The
star Sigma Octantis lies about 1 degree from the SCP, but it
is barely visible with the naked eye (magnitude 5.5).
For general visual observation, an approximate polar align-
ment is sufficient:
Содержание AstroView 90mm EQ 9024
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