the azimuth adjustment knobs on the equatorial mount in order to fit the mount onto the tripod head.
3.Thread the central support shaft up through the tripod head and into the bottom of the equatorial mount until tight. Use the upper knob on the central support shaft to do this. The equatorial mount should now be firmly con- nected to the tripod.
4.Remove the knob and washer from the bottom of the center support shaft. Slide the tripod support tray up the bottom of the central support shaft until the three tray arms are touching the legs of the tripod. The flat side of the support tray should be facing up. Make sure the “V” of each tray arm is against a tripod leg. Place the washer on the center support shaft against the tray, and follow it by threading the knob all the way up the center support shaft until it is tight against the tray. The tripod support tray pro- vides additional stability for the tripod, and holds up to five 1.25" eyepieces and two 2" eyepieces.
5.Loosen the counterweight shaft lock lever and fully extend the counterweight shaft. Retighten the lock lever.
6.Remove the knurled “toe saver” retaining screw on the bot- tom of the counterweight shaft and slide the counterweight onto the shaft. Make sure the counterweight lock knob is adequately loosened to allow the counterweight shaft to pass through the hole. Position the counterweight about halfway up the shaft and tighten the lock knob. Replace the toe saver at the end of the bar. The toe saver prevents the counterweight from falling on your foot if the lock knob happens to come loose.
Your Sirius EQ-G mount is now fully assembled and should resemble Figure 1 except for the hand controller, which will be installed and explained in Section 7 (Dual-Axis) or Section 8 (GoTo).
4. Attaching a Telescope
The Sirius EQ-G equatorial mount is designed to hold tele- scope tubes weighing up to approximately 25 lbs. For heavier telescopes, the mount may not provide sufficient stability for steady imaging. Any type of telescope can be mounted on the Sirius EQ-G, including refractors, Newtonian reflectors, and catadiotropics, provided a set of tube rings is available to cou- ple the tube to the mount. Orion sells a variety of telescope tube rings. Please visit our website at OrionTelescopes.com for details.
Tube ring attachment screw
Flat washer
Lock washer
Optical axis offset adjustment screws
Figure 3. The tube ring mounting plate.
1.Attach the tube mounting rings to the tube ring mounting plate using the screws that come with the tube rings. The screws should go through the center holes in the ends of the mounting plate and rethread into the tube rings. Note that the side of the mounting plate with the central “groove” will be facing up (Figure 3). Use a small wrench to secure the tube rings to the mounting plate.
Note: The tube ring mounting plate included with the Sirius EQ-G includes four optical axis offset adjustment screws; these are the socket head cap screws located at each cor- ner of the mounting plate. These adjustment screws will be explained further in Appendix A. For now, confirm that all four adjustment screws are sufficiently unthreaded so that the ends of their threaded shafts are flush with the top surface of the tube ring mounting plate.
Note: The optical axis offset adjustment screws should be oriented so that the threaded shaft extends upward through the top surface of the tube ring mounting plate. If the tube ring mounting plate arrives with the optical axis offset screws installed backwards, reverse their orientation before proceed- ing (Figure 3).
2.Loosen the black mounting plate lock knobs on the top of the equatorial mount. Place the mounting plate, with the tube rings attached, in the slot on top of the equatorial 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 by unthreading the knurled clamps 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 retighten the clamps.
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 the counterweight lock knob and slide the weight along the shaft until it counterbalances the tele- scope (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 then you
