The NURO Autoguider
The National Undergraduate Research Observatory (NURO) uses a 31" optical telescope owned by Lowell Observatory. This telescope allows undergraduate students from a consortium of colleges and universities to gain hands-on experience using a research quality telescope.
Despite its relatively small size, the 31" telescope when equiped with modern electronic detectors can make very high sensitivity observations. One of the limits to how faint the 31" can observe is set by how long it can make a CCD photograph of the sky. Due to mechanical variations in the pointing of the telescope, the longest unaided exposures are around 4 minutes. During longer exposures, the telescope's pointing can vary enough that images are smeared out.
An Autoguider can, as its name indicates, guide the telescope during an exposure to compensate for pointing variations.
Basically, before an exposure, the autoguider is used to select a fairly bright pointing star. The star is positioned on the AG detector. If the star image begins to wander around during the exposure, the AG detects that wander, and commands the telelescope to move so that the star is returned to the reference position. In theory, at least, the telescope should then be able to make exposures as long as desired with little loss in image quality.
This is a picture of the autoguider I am wiring up for NURO - see my astronomy site for more details.
David Shaffer Photography