Guide scopes are used in combination with autoguiders to automatically compensate for minor tracking errors while imaging. An autoguider is a small CCD camera capable of monitoring the position of a guide star. A guide scope provides the optics for the autoguider. The larger the aperture of the guide scope, the fainter the star that a given autoguider will be able to lock onto. Some of the smaller guide scopes may work fine while guiding a short focal length refractor, but not with a longer focal length Schmidt Cassegrain. Be sure to read the detailed product descriptions before attempting to use a mini guide scope with a Schmidt-Cassegrain.