Celestron 93507 manual Periodic Error Correction PEC, Using Periodic Error Correction

1.Polar align the telescope using an optional equatorial wedge. To polar align the NexStar you must select EQ North Align (or EO South Align) from the alignment options. For more information on polar aligning, see the Polar Alignment section earlier in the manual.

2.Remove all visual accessories.

3.Thread the Radial Guider onto your telescope.

4.Thread the T-Ring onto the Radial Guider.

5.Mount your camera body onto the T-Ring the same as you would any other lens.

6.Set the shutter speed to the "B" setting.

7.Focus the telescope on a star.

8.Center your subject in the field of your camera.

9.Find a suitable guide star in the telescope field. This can be the most time consuming process.

10.Open the shutter using a cable release.

11.Monitor your guide star for the duration of the exposure using the buttons on the hand controller to make the needed corrections.

12.Close the camera's shutter.

Periodic Error Correction (PEC)

PEC for short, is a system that improves the tracking accuracy of the drive by reducing the number of user corrections needed to keep a guide star centered in the eyepiece. PEC is designed to improve photographic quality by reducing the amplitude of the worm errors. Using the PEC function is a three-step process. First, the NexStar needs to know the current position of its worm gear so that it has a reference when playing back the recorded error. Next, you must guide for at least 8 minutes during which time the system records the correction you make. (It takes the worm gear 8 minutes to make one complete revolution, hence the need to guide for 8 minutes). This “teaches” the PEC chip the characteristics of the worm. The periodic error of the worm gear drive will be stored in the PEC chip and used to correct periodic error. The last step is to play back the corrections you made during the recording phase. Keep in mind, this feature is for advanced astrophotography and still requires careful guiding since all telescope drives have some periodic error.

Using Periodic Error Correction

Once the telescope has been polar aligned using the EQ North Align (or EQ South for southern hemisphere) method, select PEC from the Utilities menu and press ENTER to begin recording your periodic error. Here’s how to use the PEC function.

1.Find a bright star relatively close to the object you want to photograph.

2.Insert a high power eyepiece with illuminated cross hairs into your telescope. Orient the guiding eyepiece cross hairs so that one is parallel to the declination while the other is parallel to the R.A. axis.

3.Center the guide star on the illuminated cross hairs, focus the telescope, and study the periodic movement.

4.Before actually recording the periodic error, take a few minutes to practice guiding. Set the hand control slew rate to an appropriate guide rate (rate 1 = .5x, rate 2 = 1x) and practice centering the guide star in the cross hairs for several minutes. This will help you familiarize yourself with the periodic error of the drive and the operation of the hand control. Remember to ignore declination drift when programming the PEC.

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