Orion 7817 Calibration Procedure, Aligning the R.A. motion of the star with the crosshairs

Incorrect star alignment, loose R.A. or Dec. lock-knobs, or “cone” error. If the GoTo hand contoller 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.

Calibration Procedure

1.Insert an illuminated reticle eyepiece (not supplied) into the focuser (or diagonal) of the telescope. Confirm the telescope is properly set up and balanced, and the finder- scope is aligned with the optical tube of the telescope.

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 17). 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.

Figure 17. Aligning the R.A. motion of the star with the crosshairs.

5.Point the telescope North and set the latitude scale to your local latitude using the altitude adjustment L-bolts. Alternatively, place Polaris in the polar axis finder scope if your polar axis finder scope is accurately aligned with 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 (as shown in Figure 19a).

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 18).

8.Without moving the R.A. axis, adjust the azimuth control knobs to orient Polaris in the center of the eyepiece 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 19a &19b) This should be done as accurately as possible referencing the R.A. mechanical setting circle.

Figure 18. Adjust the telescope in Dec. (with the hand controller) to place the star on the R.A. crosshair.

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 18).

11.Carefully push the telescope in horizontal motion while observing the movement of Polaris in the eyepiece field of view (Figure 20). 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 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), according to the results of step

11.If Polaris moves toward the center when the telescope is pushed as indicated in Figure 20, loosen the adjust- ment screws near the front of the tube and tighten the adjustment screws closer to the back of the tube (Figure 21a). If Polaris moves away from the center when the tele- scope is pushed as in Figure 20, loosen the adjustment screws near the back of the tube and tighten the adjust- ment screws closer to the front of the tube (Figure 21b). Look into the eyepiece. Adjust the adjustment screws just enough to place Polaris HALF the distance back to the center of the illuminated reticle eyepiece (Figure 22).

14.Repeat steps 7 to 12 until Polaris remains in the center of the eyepiece field of view, or moves slightly around the center, when the mount is rotated about the R.A. axis.

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