BILL'S COMET AND SKY PHOTO TIPS


by William T. Hark. Copyright 1999. This may be reproduced on websites if credit and links to my page are maintained.

Introduction

Taking photos of large naked-eye comets is very easy. With some simple equipment, beautiful photos can be taken by anybody. One doesn't need to be an astronomer or own expensive telescopes and CCD imaging equipment.

Equipment

Comet photography requires a few basic items. These include a single-lens-reflex camera and a tripod. The old manual camera sitting in the attic will be better than the new computerized autofocus one. Many of the newer cameras require battery power to keep a shutter open which could fail, especially in cold weather. A camera to be used for comet photography should have a "bulb" setting or some way of keeping the shutter open for 15 to 30 seconds. It should also have a way to focus manually or be set at infinity. A camera with a hole in the photo button, which is used to screw in a cable release, is also helpful. A tripod is the other "must have" piece of equipment. The best lens is a standard 50 mm lens. Longer lenses will make the comet appear larger, but one has less available exposure time before the apparent sky motion will make the stars appear as streaks on the photos. In addition, a long lens will make getting interesting foreground objects into the photo more difficult and may cut off part of the tail by decreasing the field of view. Wider angle lenses may be useful in some cases for framing the comet with some interesting foreground object but the tradeoff is a decrease in the size of the comet. Zoom lenses have the disadvantages and advantages of longer and shorter lenses described previously. They also usually have a smaller maximal aperture which means more light and longer exposure times will be required for useful exposures In addition, a few other items will make things easier. A cable-release is useful but not absolutely necessary. It is a wire extension that is screwed into the shutter button of a camera. This enables the photographer to open and close the camera's shutter without directly touching the camera. Tripping the shutter by directly touching the camera may slightly blur the photo because of vibrations. Some cable-releases also have a locking mechanism for very long exposures enabling the photographer to leave the camera while the shutter is open. Cable-releases are usually about nine to twelve inches long, cost about eight dollars and can be bought at most photo stores. Remember that some new cameras don't have a place to screw in a cable-release; instead, they have an alternative way for long exposures. Also useful is a small pen-light for checking camera settings and equipment, a compass to note location of the comet, and a piece of black construction paper. Films used for comet photography should be high speed print film. Kodak Royal Gold 1000 is a good choice. Many people use Fuji 800 either at ASA 800 or pushed to 1000 or 1600. For black and white films, Kodak T-Max is a good if pushed. One reason why lower speed films are not used is that the time required for a decent exposure is longer which would hit the limiting factor of apparent sky movement. With a 50 mm lens, exposures of more than about 28 to 30 sec will make stars appear as little streaks on the photo.

Timing

This is critical for good comet photography. The times of a comet's appearance above the horizon should be noted. Magazines, such as Sky and Telescope, newspapers, and sources on the Web will list the best times when a comet will appear. The elevation above the horizon affects the visibility of the comet. The lower it is, the less bright and the greater chance clouds will obscure it. One should also note the times of sunset and sunrise. There is nothing worse than getting set up in a good location and having the approaching dawn ruin a good photo op. Remember that a little bit of light from the sun will be much more apparent on a timed exposure of the sky with fast film. In the evening, wait at least an hour after sunset if possible. Watch the darkening sky and wait at least 15 to 30 minutes after the last evidence of light has vanished. The moon will also ruin comet photos. The moon, even if only partial or on the other side of the sky, will wash out sky photos. The effect is more noticeable on the photo than while observing. The weather is very important because only a few clouds or haze can ruin a comet photo. Monitor the weather carefully. During the best viewing times, there may be only a few days of clear sky to obtain a photo. Don't miss an opportunity.

Location

Pick a dark location to photograph. The comet may be visible with lights around but the lights will greatly reduce the amount of comet tail visible on photos. Like the moon, the effect is more noticeable on photos than while observing. Go away from cities or towns in the direction of the comet. If the comet is in the Northwest sky, make sure there is not a large city to the NW of ones location. Remember that city lights can be seen even thirty miles from a dark location. Small points of light in the distance (ie. a farmer's porch light) won't have too much effect on the photo, but the less the better. Also pick an area that is off a main road, that is reasonably safe, and off private property. Bring another person for extra safety and to share the beauty of the comet.

Composing and Taking the Photos

Before going out, make sure you are familiar with the equipment and setting up the tripod. If possible, go out while there is still some light if photographing in the evening. You will know where the comet is while finding a good location, but will not be wasting valuable photo time. After setting up the camera, frame the comet with the head slightly to one side. Remember that the tail goes further on photos than is visible and extra room should be left on the photo. Also try to have some objects in the foreground (not covering the comet) to add interest and perspective. Trees and mountains are good. Start the exposures at about 15 seconds. Increase by about three seconds and take another photo until a 30 second exposure time is reached. Time the exposures by counting or using a watch. Do the exposures in a set order because you will want to know them while looking at the negatives. Use the maximal f-stop, usually about f 1.8 or 2.8 on most cameras and focus on infinity. Then vary the composition of the photos or try a different location. For maximal sharpness, use a black card. Place it in front of the camera (not touching) and open the shutter, then remove it for the duration of the exposure. When done, place the card across the field of view before closing the shutter. The opening and closing of the shutter along with the movement of the mirror inside can induce vibrations.

Development

This is the one case where using a one-hour photo developer is good. By reviewing the photos the next day, mistakes can be fixed and photos can be improved. Remember that there is a wide range of printing and the photos can be printed more light or dark as needed.

Special Cases

A comet over a known landmark or a lighted building can be very interesting but is difficult because of differences in exposures required. In many cases, the building would be over-exposed to obtain a good comet photo. Try using a black card to cover the building during most of the exposure, then remove it for a second or two before closing the shutter. Multiple attempts would be required and exposure times of both the building and the comet will need to be varied. It is worth a try as the results can be very nice. The Rotunda at the University Of Virginia makes a nice foreground for the comet in one example. Remember that the light level will be increased around many buildings which will decrease the amount of the comet that is visible.

After the Comet

Hale-Bopp is gone but there are other opportunities for night sky photos. The Milky Way is very beautiful on a clear dark night and photographs well using these techniques. Many more stars will be seen on the photos than are observed with the naked eye. Nebulae will photograph, often appearing on photos while not visible during observation. Also try photographing a meteor shower if there is no moon and the sky is clear. Aim the camera toward the place where most of the meteors are coming and hope for the best. It will be by chance (like lightning). As with comets, don't leave the shutter open longer than 30 seconds unless one wants the stars to be little lines from the motion of the Earth.

Good Luck!


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