Bringing home memories of the stars
One of the most popular activities in amateur astronomy is photographing the objects seen in the sky. For those families and friends of amateur astronomers who don't wish to venture out into the night, this provides a fun and easy way to view astronomical objects.
The difficulty in taking astronomical photographs can range anywhere from incredibly easy, to heart- breakingly difficult.
There are, essentially, three major forms of astrophotography. This week, we will cover the easiest of these. This will require a 35 mm camera, with a bulb, or "B" setting. When choosing film, it is important to get a fast film, most often 400 ASA. There is 1000 ASA film produced, but this is often too grainy for most purposes.
The first type of photograph, and the easiest, is taking photos of the star fields themselves, with no magnification, apart from that which your camera provides on it's own. This will allow you to photograph the constellations, star trails, and meteor showers.
If you wish to photograph a constellation, Orion say, or the big dipper, set your camera on a tripod, or balance it on a fencepost, or the hood of a car. For best results, hook the shutter release of your camera to a cable release. This is a cable which allows you to take photographs with a minimum of jiggling occurring to the camera, and can be bought in any camera store for five to ten dollars. Set the camera pointing towards the area of the sky which you wish to photograph. Advance your film, and set your camera to the bulb setting. Release the shutter, and begin counting. Even with a cable release, there will still be some jiggling occurring. For best results, hold a black piece of paper in front of the camera, release, wait a few seconds, then remove the paper, and begin timing the photo.
In order to get nice photos of constellations, expose your negative for between 10 and 30 seconds. Any time less than 10 seconds will result in few stars being shown, and any time over 30 seconds will result in streaking, due to the rotation of the Earth. At the end of your exposure, release the lock on the cable release, ending the exposure. Again, for best results, hold your black piece of paper in front of your lens when you wish to end your exposure, and only then release the lock.
It is important with this sort of photography that the lens you are using is open as wide as possible. This is usually f/ 2.8. Try taking several photos at different time intervals in this range, and see the different results possible.
Another variation on this idea is to allow the stars to streak, producing what are known as star trails. These are quite often beautiful, and easy to accomplish. Simply point your tripod mounted camera to one area of the sky, and expose, using the tricks above, anywhere from one minute to several hours. This will show the paths which the stars follow through the course of the night.
If your camera is pointed towards the north star, your picture will show a field of stars, circling around the center star, Polaris. They will form a series of multi colored concentric rings on your photograph. Very beautiful. Try this with some horizon showing on the bottom. If you are lucky enough (or far sighted enough) to be taking photographs on the night of a meteor shower, the meteors will show up as streaks through the trails of stars. This is also the best way of counting meteors during a shower.
Take a star trail picture of the constellation which the meteor shower will be emanating from, and record the amount of time each frame was exposed. When the photos are developed, count the number of meteor streaks on the frame, and then calculate the number of meteors per hour at that time. For instance, if one exposure was 10 minutes (or one sixth of an hour), and there are 5 meteor streaks on it, you can be fairly sure that there were around 30 meteors per hour that night, in that area of the sky. You counted 5 in the 10 minutes you exposed the negative for, and there are 6 ten minute periods per hour, thus you would have (most likely) recorded 30 meteors had you exposed that frame for one whole hour.
The best advice I ever read on astrophotography was this. "Take a whole lot of photographs, at a whole lot of different settings, and throw most of them away".
Clear skies, and good viewing.
