Orion EQ-G instruction manual Appendix B Periodic Error Correction PEC, PEC Training

view (Figure 19). 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 corner of the mounting plate, (Figure 3) according to the results of step 11. If Polaris moves toward the center when the telescope is pushed as indicated in Figure 19, loos- en the adjustment screws near the front of the tube and tighten the adjustment screws closer to the back of the tube (Figure 20a). If Polaris moves away from the center when the telescope is pushed as in Figure 19, loosen the adjustment screws near the back of the tube and tight- en the adjustment screws closer to the front of the tube (Figure 20b). Look into the eyepiece. Adjust the adjust- ment screws just enough to place Polaris HALF the dis- tance back to the center of the illuminated reticle eyepiece (Figure 21).

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.

Note: This calibration method can be applied to both refract- ing and reflecting telescope designs. Differences in the optical path of telescopes do not affect how the telescope tube and tube rings should be adjusted on the mounting plate.

Figure 21. Using the optical axis offset screws move Polaris halfway to the eyepiece’s center.

ing method to reduce the amplitude of the worm gear errors. By recording a full cycle of guiding actions, the Atlas EQ- G can compensate for drifting in the R.A. sidereal tracking caused by periodic errors. The following instruction will lead you on a step-by-step procedure for performing the PEC.

Note:The PEC training function is recommended for advanced users with interest in long-exposure astrophotography only. Careful guiding is required. Standard sidereal tracking is suf- ficient for all casual visual applications of the Atlas EQ-G, and PEC training is not required.

PEC Training

1.Perform an accurate polar alignment using the polar axis finder scope.

2.Manually point or electronically slew the telescope mount- ed on the Atlas EQ-G to a star with a small value Dec. coordinate (Dec. between +10° and –10°). This object will be used as the guide star.

3.Activate “Sidereal Tracking” from the Setup menu (see “Setup Functions”). Once tracking has initiated, press ESC to return to the Setup menu.

4.Rotate the reticle eyepiece in the focuser (or diagonal) until the R.A. movement of the star becomes parallel to one of the illuminated crosshairs

5.Move the guide star designated in step 2 to the center of the eyepiece field of view using the direction buttons.

6.On the hand controller, select “PEC Training” in the Utility Functions and press ENTER.

Note: Utility Functions can be accessed by pressing the UTILITY quick rererence button on the hand controller.

7.Select the R.A. guide speed for the PEC Training.You have two guide speed choices: 1) 0.25X and 2) 0.5X. Press the numeric button 1 to choose a guide speed of 1.25X or press 2 to choose a guide speed of 1.5X.

8.The Atlas EQ-G hand controller will display the current time once the guide speed has been selected, indicating the recording has begun.

9.Using the left or right direction button only, move the tele- scope so the guide star remains centered in the eyepiece field of view (Figure 21). Repeat as necessary.

The Atlas EQ-G hand controller will record the manual guid- ing actions for 8 minutes in order to characterize the periodic

Appendix B: Periodic Error

Correction (PEC)

Using the PEC functions requires an illuminated reticle eye- piece capable of producing at least 300X magnification when used with your telescope. For best results, the true field of view should not exceed 10 arcminutes.

Periodic errors are inherent in almost all worm gears due to
slight eccentricities and misalignments. The PEC (Periodic	Figure 22. Drifting caused by periodic error.
Error Correction) Training function provides a manual correct-

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