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pleting the star alignment, choose a bright star in the western
sky from the Sirius EQ-G object database and press ENTER
to slew the telescope to the star. If the optical axis is perfectly
aligned to the R.A. axis, the telescope will accurately put the
star in the center of the eyepiece. This shows that there is no
significant cone error in your telescope setup and you will not
need to perform the calibration. It is acceptable if the star is
slightly off-center as long as it appears in the eyepiece field of
view and reasonable close to the center. Many factors deter-
mine the pointing accuracy of the Sirius EQ-G. Incorrect star
alignment, loose R.A. or Dec. lock-knobs, or cone error. If the
Sirius EQ-G puts the star outside the eyepiece field of view,
you need to determine which of these factors is causing the
pointing inaccuracy. To determine if the inaccuracy is caused
by cone error, simply move the telescope about the R.A. axis
by pressing the Left or Right direction button. If the star can
be moved into the eyepiece field of view without adjusting the
Dec. axis, it is likely that cone error exists in your telescope
setup.
cone Error calibration Procedure
1. Insert an illuminated reticle eyepiece (not supplied) into
the focuser (or diagonal) of the telescope. Confirm the tele-
scope is properly set up and balanced, and the finderscope
is aligned with the optical tube of the telescope. The mount
also needs to be accurately polar aligned.
Note: Steps 2 to 4 are to identify R.A. and DEC movements in
the reticle eyepiece. If you are already familiar with the move-
ments, proceed to step 5.
2. Find a bright star and position the telescope so the star is
centered in the eyepiece field of view.
3. Look into the eyepiece. Move the telescope about the R.A.
axis using the R.A. direction buttons on the hand controller
while carefully observing the movement of the star.
4. Keep moving the telescope about the R.A. axis back and
forth to keep the star within the eyepiece field of view.
Rotate the eyepiece in the focuser (or diagonal) until the
movement of the star becomes parallel to one of the illu-
minated crosshairs (Figure 15). This crosshair will repre-
sent R.A. movement in the course of this procedure, and
the perpendicular crosshair will represent Dec. movement.
Tighten the set screws to secure the eyepiece in position.
Make sure the eyepiece will remain stationary while the
telescope is moved.
16
Figure 15.
Aligning
the R.A. motion of the
star with the crosshairs.
5. Point the telescope north so the tube is parallel with the
R.A. axis of the mount.
6. Loosen the R.A. lock knob and rotate the telescope about
the R.A. axis until the counterweight shaft is parallel to the
ground (Figure 17a).
7. Using the Dec. direction button on the hand controller,
adjust the telescope in Dec. so Polaris lies on the R.A.
crosshairs of the illuminated reticle eyepiece (Figure 16).
Figure 16.
Adjust the telescope in Dec. (with the hand controller)
to place the star on the R.A. crosshair.
8. Without moving the R.A. axis, adjust the azimuth control
knobs (Figure 2) to orient Polaris in the center of the eye-
piece field of view. Adjustment in Dec. axis using the hand
controller may be necessary.
9. Loosen the R.A. lock knob and carefully rotate the tele-
scope 180° about the R.A. axis (Figure 17a &17b) This
should be done as accurately as possible referencing the
R.A. mechanical setting circle.
10.Adjust the position of the telescope in the Dec. axis so
Polaris lies on the R.A. crosshairs of the illuminated reticle
eyepiece (Figure 16).
11.Carefully push the telescope in a horizontal motion while
observing the movement of Polaris in the eyepiece field of
view (Figure 18). This will determine which direction (left
or right) moves Polaris closer to the center of the eyepiece
field of view.
12.Carefully and gently loosen both the tube ring attachment
screws (Figure 3) by a couple of turns.
13.Make adjustments to the optical axis offset adjustment
screws (the socket head cap screws located at each cor-
ner of the mounting plate, see Figure 3) according to the
results of step 11. If Polaris moves toward the center when
the telescope is pushed as indicated in Figure 18, loosen
the adjustment screws near the front of the tube and tight-
en the adjustment screws closer to the back of the tube
(Figure 19a). If Polaris moves away from the center when
the telescope is pushed as in Figure 18, loosen the adjust-
ment screws near the back of the tube and tighten the
adjustment screws closer to the front of the tube (Figure
19b). Look into the eyepiece. Adjust the adjustment screws
.
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