field rotation

The field rotation is the rotation of a star field about the center that occurs in telescope with an altazimuth mounting because the motion is not about the polar axis. Field rotation is seen in photographs or CCD images as stars trailed around the center of the picture. If a telescope has an equatorial mounting, an attached camera correctly tracks the subject across the sky, since the telescope and Earth now rotate about the same axis. By placing an altazimuth telescope on a wedge, field rotation can be eliminated.