You will need a camera that has a "B" setting so that you can leave the aperture open for as long as you want. Automatic cameras and flash bulbs are no help in taking pictures of stars and nebulae. Single lens reflex cameras are ideal. A tripod is also handy (although you can use a clamp to attach the camera to any fixed object, such as a fence), and a cable release will reduce vibrations during the exposure (caused by you holding your finger on the button). A cable release usually has a lock and quick release mechanism - have a fiddle with it in the daytime until you are happy that you know how it works, and use it with the camera before you put any film in it.
For photos using a standard 50mm lens, you can expose for one to two minutes with only a minimal amount of "star trailing". Star trailing is caused by the spin of the Earth, making the stars appear to move across the sky at night just as the Sun does during the day. My photo of Comet Hyakutake which appeared in "Sky and Space" (August 96 issue) was approximately one minute. To gather enough information on the film in that time, I used 400 ASA colour film, but you can go even faster if you don't mind the graininess. Much depends on whether or not you are going to want to make enlargements.
Whatever exposure time you use, you will get less trailing near the south celestial pole, and more if you are shooting near the northern horizon. This is a good time of year to attempt to capture the Southern Cross region.
A wide-angle lens will give you a larger area of sky, and less noticeable trailing. You can expose for up to 5 minutes, which will bring out features like the Eta Carinae nebula and the Coal Sack.
Zoom lenses, whilst you might think would give you a better look at an object, really only tend to exaggerate the trailing. These pictures look quite interesting, though, and you can go for special effects if you want to. Progressively de-focusing the camera will spread the star image and bring out the colour of the stars. Centre on a red giant such as Antares if you want to experiment.
Experimentation is the key. For every exposure you want to make, make three. Start with basic times as stated above, and then do one for half as long, and one for twice as long. You will need to get to know your own location. Light pollution will limit the exposure times because it will wash out the faint objects and reduce the overall contrast. And don't expect every exposure to turn out - you may only get one or two good shots from a roll. Start with a 12 exposure roll and test the local labs before you get too deeply involved.
You will need to specify to the lab that they are night sky photos. Do a daytime exposure for the first and the last shot on the roll, as a guide for the labs. You will have to tell them to print every shot, even if it looks like there is nothing on the film. And when you go back to pick them up, you may need to jump up and down to make them understand!
You may not be able to make head or tail of your pictures when you get them back. So before you start shooting, get a notebook and detail every exposure (exposure number, date, time, lens, exposure time, aperture setting should be fully open all the time, and intended subject). Also note the type of film you have used, and give each roll a number. Then when the pictures come back, you should be able to match your negatives to your notes, and your pictures to your negs. Then number the pictures on the back according to roll number and exposure number.
If you want a good reference book which covers all aspects of astrophotography, get a copy of Michael Covington's "Astro-photography for the Amateur". Good luck, happy snappers!
By Lesa Moore, Senior Guide, Koolang Observatory and reproduced by permission.