An autoguider need not be an independent unit; some high-end CCD imaging units (such as those offered by SBIG) have a second, integrated CCD sensor on the same plane as the main imaging chip that is dedicated to autoguiding.
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The device has a CCD or CMOS sensor that regularly takes short exposures of an area of sky near the object.
A number of smaller telescopes are co-mounted to the main telescopes to act as guidescopes, widefield telescopes or H-alpha solar telescopes.