Meade LX200 telescopes may be operated in the altazimuth mode (i.e. without polar alignment) for all visual applications and for photographic or CCD imaging exposures of up to about five minutes duration. During longer photo or CCD exposures in the altazimuth mode, however, an effect called field rotation becomes evident. This means that even if the telescope is perfectly guided on a central star during a long exposure, stars at the edge of the field appear to rotate about the field center during the exposure. The result is that stars away from the field center appear to trace small concentric arcs on the film, rather than starpoints. This effect, which in no way relates to the accuracy of the telescope's computer or internal alignment, occurs on all altazimuth-mounted telescopes, and is caused by the telescope not being polar aligned.
Field rotation can be cured with the simple addition of an equatorial wedge which permits precise polar alignment, negating all field rotation. Alternatively, the optional #1220 Field De-Rotator may be attached to the rear cell of any LX200 model, simplifying field operation of the telescope, since no wedge is required. With the #1220 De-Rotator attached to the telescope's rear cell, other accessories can in turn be threaded to the #1220 unit.
The #1220 is easy to use! Just align the LX200 telescope using the 2-star technique or other method described in the LX200 manual, and, automatically, signals are fed through the RS-232 port on the LX200 control panel to the Field De-rotator, causing it to rotate at the correct speed and precisely counter the effects of altazimuth-induced field rotation.