Astronomical Society of South Australia
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Comet Photography
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Amongst all the wonders of the universe, comets arouse more than their fair
share of interest. Is it because they are ephemeral beasts, here today and gone
tomorrow, perhaps forever, or is it that they are everchanging on a daily or
weekly time scale? Whatever the reason, they capture the interest of the general
public and the dedicated amateur and professional astronomer alike. So the
question that frequently arises is "How do I photograph a comet?"
There are several considerations which I will deal with in turn. The CameraAn SLR camera, preferably manual and with a non-electronic shutter is essential. Exposures to capture a comet will range from a few minutes to perhaps 15 minutes, so a cable release which will allow the shutter to be locked open for this period (the "B" setting on the shutter speed dial) is also necessary, as of course is a firm tripod on which to mount the camera.What lens to use? Comets with their tails cover a surprising distance across the sky, frequently 10-15 degrees (a hand span at arms length) so a moderate wide-angle lens (i.e. 35mm focal length) is ideal, but a normal 50mm lens is still OK. Set the lens to it's largest apperture (i.e. f =2.0) as the distant end of the comet's tail is very faint. For more detail of the comet head use a 135-200mm telephoto lens, but don't expect to capture fine detail of the comet head itself, it is after all, buried in a shroud of dust. Finally, check the lens focus and set to infinity. The FilmComets move haven't you noticed. So unless you want a somewhat blurred photograph, a fast film (ASA 400 to 1000) is necessary. Print or slide film doesn't matter, however if you use print film get the photo lab to print your negatives at various densities to get the best effect. With these film speeds, an exposure of 5 minutes will show the comet head and the brightest part of it's tail, for capturing the full extent of the tail, go for 15 minutes. Don't be afraid to take several photos of increasing time but check the position of the comet in the camera viewfinder before each photo.Where To Take The PhotographsThe limiting factor for all astrophotographs is the night sky fog limit. This is the time it takes for the background lighting to overwhelm the object being photographed. If you live in a city, this may be as short as a couple of minutes (if using fast film) especially if bright flood lights or street lights are nearby. It really is best to get out of town. This is especially so when the comet (or any other object for that matter) is very low in the sky, as Comet Hale-Bopp was for us southern hemisphere observers. Finally, go where you won't be troubled by car headlights, they really are annoying and will ruin any long exposure photograph.So, there it is. Fast film, wide-angle lens, dark sky and a 10 minute exposure and you are sure to capture a comet. Oh, and by the way, don't be afraid to have a tree, windmill or old house in the foreground, it adds interest to your photographs. Happy shooting! |