Appendix B Periodic Error Correction PEC, PEC Training

Figure 22. Using the optical axis offset screws move Polaris halfway to the eyepiece’s center.

Appendix B: Periodic Error Correction (PEC)

(Requires an illuminated reticle eyepiece 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 Error Correction) Training function provides a manual correct- ing method to reduce the amplitude of the worm gear errors. By recording a full cycle of guiding actions, the SkyView Pro GoTo system can compensate for drifting in the R.A. sidere- al tracking caused by periodic errors. The description below 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 astro- photography only. Careful guiding is required. Standard sidereal tracking is sufficient for all casual visual applica- tions of the SkyView Pro GoTo system, and PEC training is not required.

PEC Training

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

2.Electronically slew the telescope mounted on the SkyView Pro 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 (matches) 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 0.25X or press 2 to choose a guide speed of 0.5X.

8.The SkyView Pro GoTo 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 23). Repeat as necessary.

The SkyView Pro GoTo hand controller will record the manual guiding actions for 8 minutes in order to characterize the peri- odic errors. Pressing ESC will immediately stop the recording and exit from the PEC Training function.

Note: Guiding actions are recorded even when the PEC training is stopped midway. The PEC + sidereal tracking will not be accurate until a full cycle of the PEC Training is performed.

Figure 23. Drifting caused by periodic error.

7817 specifications

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