Celestron Advanced VX Mount and Tripod Advanced VX - Page 29

This device allows you to photograph and guide through the telescope simultaneously. In addition, you will need a T-Ring to attach your camera to the off-axis guider. Other equipment needs include an autoguider, which is a small camera that attaches to the off-axis guider and keeps your guide star centered while you are imaging with your main camera. Here is a brief summary of the technique. 1. Polar align the telescope. For more information on polar aligning, see the Polar Alignment section earlier in the manual. 2. Remove all visual accessories. 3. Thread the off-axis guider onto your telescope. 4. Thread the T-Ring onto the off-axis 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. F ocus the telescope on a star. 8. Center your subject in the field of your camera. 9. Using your autoguider, find a suitable guide star in the telescope field. This can be the most time-consuming part of the 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) Periodic Error Correction, or 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 imaging quality by reducing the amplitude of the worm errors. Using the PEC function is a three-step process. First, the Advanced VX mount needs to know the current position of its worm gear, so it has a reference when playing back the recorded error. Next, you must guide using an autoguider for at least 10 minutes during which time the system records the correction you make. (It takes the worm gear 10 minutes to make one complete revolution). 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. 1. Find a bright star relatively close to the object you want to image. 2. Insert the autoguider into the eyepiece holder of your telescope. Orient the guider so that one axis of the sensor is parallel to the declination axis while the other is parallel to the R.A. axis. 3. Focus the telescope, and study the periodic movement. 4. Plug the autoguider cable into the autoguider port on the mount's electronics panel. 5. To begin recording the drive's periodic error, press the MENU button and select PEC from the Utilities menu. Use the Up/Down scroll buttons to display the Record option and press ENTER. When you are ready to record, press the ENTER button again to begin. You will have 5 seconds before the system starts to record. The first time each observing session that PEC record or play is selected, the worm gear must rotate in order to mark its starting position. If the worm gear rotation moves your guide star outside the field of view of the eyepiece, it will have to be re-centered before the recording begins. Note: Once the worm gear is indexed, it will not need to be positioned again until the telescope is turned off. To give yourself more time to prepare for guiding, it may be necessary to restart PEC recording after the worm gear has found its index. 6. After 10 minutes, PEC will automatically stop recording. 7. Point the telescope at the object you want to image and center the guide star on the illuminated cross hairs. You are ready to play back the periodic error correction. 8. O nce the drive's periodic error has been recorded, use the Playback function to begin playing back the correction for future imaging guiding. If you want to re-record the periodic error, select Record and repeat the recording processes again. The previously recorded information will be replaced with the current information. Repeat steps 7 and 8 to playback the PEC corrections for your next object. Does the PEC function make unguided astroimaging possible? Yes and no. For solar (filtered), lunar and piggyback (up to 200mm), the answer is yes. However, even with PEC, autoguiding is still mandatory for long exposure, deep sky astroimaging. Using Periodic Error Correction Once the telescope has been properly polar aligned, select PEC from the Utilities menu and select the Record option. Here's how to use the PEC function: ENGLISH I 29