Balancing A Telescope; Setting Up And Using The Equatorial Mount - Orion Atlas EQ-G Instruction Manual

Dec. lock lever
(not shown)
Front opening
Azimuth
adjustment
knobs (2)
Figure 5.
The Atlas EQ‑G mount.
mount. Position the mounting plate so that it is centered in
the slot. Re‑tighten the mounting plate lock knobs until the
plate is secure.
3. Open the tube rings and lay the telescope optical tube in
the rings at about the midpoint of the tube's length. Rotate
the tube so that the focuser is at a convenient height for
viewing. Close the tube rings and tighten them.
Note: The Atlas EQ‑G mount is very heavy. Alone it weighs 54
lbs. With a large optical tube and counterweights it can easily
weigh over 100 lbs. Keep this in mind when moving the tele‑
scope even small distances, and use assistance when need‑
ed. It is best to remove the optical tube and counterweights
when moving the mount.
Note: Some telescope optical tubes (specifically Schmidt‑
Cassegrains and Maksutov‑Cassegrains) have a mounting
plate connected directly to the tube. For these telescopes,
optional tube rings are not required. Simply follow step 2
(above) to connect the telescope to the mount.

5. Balancing a telescope

To ensure smooth movement of a telescope on both axes of
the equatorial mount, it is imperative that the optical tube is
properly balanced. We will first balance the telescope with
respect to the right ascension (R.A.) axis, then the declination
(Dec.) axis.
1. Keeping one hand on the telescope optical tube, loosen
the R.A. lock lever. Make sure the Dec. lock lever is locked,
for now. The telescope should now be able to rotate freely
about the right ascension axis. Rotate it until the counter‑
weight shaft is parallel to the ground (i.e., horizontal).
2. Now loosen both counterweight lock knobs and slide the
weights along the shaft until they exactly counterbalance
the telescope (Figure 4a). That's the point at which the
shaft remains horizontal even when you let go with both
hands (Figure 4b). If the telescope refuses to balance
than you have either too much or too little counterweight.
Remove a counterweight, or add optional counterweights
if needed.
3. Retighten the counterweight lock knobs. The telescope is
now balanced on the right ascension axis.
R.A. lock lever
4. To balance the telescope on the declination axis, first tight‑
en the R.A. lock lever, with the counterweight shaft still in
the horizontal position.
Polar axis
finder scope
5. With one hand on the telescope optical tube, loosen the
Dec. lock lever. The telescope should now be able to rotate
Latitude scale
freely about the declination axis.
Latitude
6. Loosen the knurled ring clamps on the tube rings a few
adjustment L‑bolts
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 4c).
7. Position the telescope in the tube rings so it remains hori‑
zontal when you carefully let go with both hands. This is
the balance point for the optical tube with respect to the
Dec. axis (Figure 4d).
8. Retighten the knurled ring clamps.
The telescope is now balanced on both axes. When you loos‑
en the lock lever on one or both axes and manually point the
telescope, it should move without resistance and should not
drift from where you point it.
6. 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 rotation (from
west to east). An equatorial mount (Figure 5) is designed to
compensate for that motion, allowing you to easily "track" the
movement of astronomical objects, thereby keeping them
from drifting out of your telescope's field of view while you're
observing.
This is accomplished by slowly rotating the telescope on its
right ascension (R.A.) axis, using the built in motor drive. 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 align‑
ment is achieved by pointing the mount's right ascension axis
at the North Star, or Polaris. It lies within 1° of the north celes‑
tial pole (NCP), which is an extension of the Earth's rotational
axis out into space. Stars in the Northern Hemisphere appear
to revolve around the NCP.
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