The declination drift method allows you to perfect the polar alignment of your telescope. When finished, your telescope will track as accurately as possible. That's why this is the method used by many astroimagers. Even the slightest drift due to misalignment can ruin an astrophoto. This method allows you eliminate declination drift, leaving only periodic error and the resulting right ascension drift to correct during exposures. The declination drift method requires time and patience. Plan to spend at least an hour the first time you attempt it. At minimum, this method requires 30 minutes. If you haven't performed a rough polar alignment, do so before moving on to the first step.
|STEP 1: Correcting East-West Misalignment|
This method fine tunes the alignment of the telescope by addressing misalignment in each axis. First, correct any east-west misalignment. Rotate your telescope in declination to 0 degrees. Center a star that is due south along the celestial equator. This star should be within 5 degrees of the celestial equator and your local meridian. Insert an illuminated reticle eyepiece, rotating the eyepiece so the lines are aligned east-west and north-south. Allow the telescope to track for 5 minutes and ignore any east-west drift:
Adjust the east-west orientation of the telescope mount based on the star's drift. Repeat this step until all north-south drift is eliminated. Then, move on to the next step.
|STEP 2: Correcting North-South Misalignment|
Rotate your telescope in declination to 0 degrees. Center a star low in the eastern sky. This star should be within 5 degrees of the celestial equator. Check the illuminated reticle eyepiece to make sure the lines are still aligned east-west and north-south. Allow the telescope to track for 5 minutes and check the position of the star. Again, ignore any east-west drift:
Adjust the tilt of mount to correct for any north-south drift. Repeat this step until all north-south drift is eliminated. If you do not have access to the eastern horizon, you can use a star low in the west. Just reverse the corrections based on the drift. When you've completed this second step, repeat the procedure beginning with Step 1. Any remaining north-south drift should be eliminated after completing both steps of this procedure a second time. Your telescope is now ready for long exposure astrophotography.
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Revised: February 11, 2002 [WDF]