CAPTURING A COMET ON FILM
Although photographing a comet is a challenging task, the results can be pectacular.
Photographers have to be aware of two things: first, that the star field moves in response to the Earth's rotation; second, that the comet moves slowly in the field of stars. When taking long exposures, either through a telescope or with your camera piggybacked on a telescope, you will need to guide it. You can guide your telescope on the comet if the coma is sharply defined. More often, however, the comet will be diffuse, without a selid point to focus on. In that case, center the guiding telescope on a star. If the exposure lasts for less than 10 minutes, it is unlikely that the comet will show perceptible motion among the stars.