Depending on the aim of the meteor photography, there are two major branches: photography of faint meteors and fireball patrol photography. The material regarding film and film realted techniques is now essentially obsolete but is maintained for reference. New material regarding meteor imaging with modern Digital SLR cameras is currently being produced and will be available shortly.
Digital imaging and techniques
Digital SLR cameras have revolutionized meteor imaging.
Much of the basic information regarding lenses from the era of film is still valid. The essence is to capture as much light as possible in order to image as faint a meteor as possible. Thus there is still the requirement for fast lenses. HOWEVER, perhaps the key operational difference between film based imaging and digital imaging is reciprocity failure. Digital sensors are essentially linear detectors of light and as such do not suffer reciprocity failure in practical terms. In effect what this means is that whilst film exposures may have been several minutes long most digital imaging is done with exposures of less than one minute.
Although manufacturers maintain the use of ISO settings on digital SLR’s this has little bearing for scientific imaging. The ISO number can be thought of as a “gain setting”. The higher the ISO number the higher the gain. (This is effectively a mimic for film ISO ratings.)
Being electronic sensors with amplifiers on chip the higher the gain also means higher noise. This effect is seen as an increasing “graininess” to the image (another analogue to films, the higher the ISO the more grainy the image although the root causes are different).
Even under very dark skies exposures of 60 seconds at ISO 1600 with a moderately fast lens will start to capture significant skyglow. Of course with wide field and generally slower lenses (f2.8 and slower) the lack of reciprocity failure means longer exposures can be made if wished without too much image degradation. Longer exposures will ultimately pay a penalty of increased electronic noise.
The other key operational benefit of digital over film is immediacy of results. There are no chemical processing requirements. This offers huge flexibility in the observer being able to take test exposures and adjust the necessary settings to optimise results in real time during a meteor observing session.
Camera and lens for photography of faint meteors
The camera body has no great influence, since it is just the film holder. Of course, the camera must allow time exposures and the easier it is to handle in the dark the better it is suited for astronomical purposes. In particular, problems may occur with cameras driven by electronics. If it is not possible to switch off the automatic controls it may not be possible to make long exposures or the batteries may wear off very quickly. Also cold winter nights are likely to lower the performance of the batteries. Long exposures are possible only if the camera shutter has either a ‘B’ or a ‘T’ position. (‘B’ implies that the shutter is open as long as you push the release button. ‘T’ opens the shutter once you push the release button, and it remains open until you push it again.) If you use ‘B’ on your camera, you will need a lockable cable release, while ‘T’ allows exposures without such a device. Sometimes a cable release may cause troubles. Some cable releases are badly affected by humidity or cold, and should be tested before each use.
The lens is of essential influence for the result. It must allow a good definition and should be sufficiently fast. Very good results can be obtained with the f/1.8, f=50 mm standard lens of small cameras. Unless very short exposure times are applied, it is not useful to use a faster lens. Longer focal lengths more often result in truncated meteor trails, unless the cameras is pointed close to the radiant of the active shower. Shorter focal lenghts often result in disappointing photographs, not in more meteors.
Of course, when you have another type of lens available you can use it without problems. Within a certain range of focal lengths (15mm…80mm) we may compare the effectiveness of different lenses using the simplified measure E, defined as: E = d2 / f, where d is the linear aperture of the lens, and f is the focal length,both in mm. If you prefer to use the aperture number r, you may write: E = f / r2.
Some construction work is required when you want to heat the lens of your camera. Unless you operate in a very windy or arid area, dew will form on the lens of your camera during the night when it cools down. You can heat your lens (or the air in front of your lens) with one or more electrical resistors, connected to your car battery (assuming you drive out of the city to a dark spot). A possible construction is drawn to the right, using a small piece of 2 inch plastic pipe that fits around the lens.
Films for meteor photography
For reference only
The information here is essentially obsolete due to the dominance of digital imaging now. The pages are being kept for reference.
The other major component is the film: today, high sensitive films (ISO 3200/36) with reasonable grain structure (such as the so-called T-grain; T standing for tabular) are available. But it is not primarily a large ISO number which guarantees success with meteor photography. Every emulsion differs from another particularly in its behaviour during long exposures, i.e. when the exposure times exceed a minute or so. Furthermore, the trade names of films vary from country to country and are also subject of change with time, so it is of little use to list all the possible sorts of films presently available. Good examples are Ilford’s HP-5 and Fuji’s Neopan 1600 (which both can be pushed to ISO 3200/36). However, it is up to the photographer to decide which film to buy: select the fastest film with as fine a grain structure as possible, within your own budget. If you photograph very frequently it is worthwile to buy film in boxes of 30 m length and spool them in cassettes yourself.
Choosing a suitable film
Exposure times should be of the order of 10 to 15 minutes for optimal results, but on very dark locations exposure times up to 30 minutes still give reasonable results. Again, you have to make some experiments which show the best values for your observing site. These figures will also depend on the actual conditions, like haze or moonlight. Exposures which lead to a considerable blackening of the background should be avoided. Here, again, it is difficult to give fixed recommendations. Some more information can be found in the IMO’s Photographic Handbook.
If a meteor appeared during the exposure, it is advised to finish the exposure very soon in order to avoid later disturbances which may badly affect the image (various accidents may always happen).
Developing your films
Developing your films is easier than many might think. You do not need complex darkroom equipment — a small developer tank will do. Furthermore, you can influence the result (pushing etc.), while professional labs might let you know that ‘there is nothing on the film’.
Instructions for films give sufficient information for various developing procedures. In any case it is best to choose a developer which makes use of the film’s sensitivity. A fine grain developer does not only have a good influence on the grain size, it also produces a rather low-contrast image which allows to transform a very wide range of brightnesses into different amounts of ‘blackening’.
Finally, it is strongly recommended to mark your films unambiguously already during the exposures and to keep a logbook. Otherwise the identification of meteor trails and the determination of the exposures may become hopeless. The essential data to note are the begin and end of the exposure, the times of bright meteors (if seen), and the region of the field of view for identification or search for fainter trails which may be missed during a first inspection of the film. If you do regular photographic work, you will find it useful to have a reference number or designation for each film or meteor negative. If you do not want to store the entire film, it is recommended to keep the negatives showing a meteor AND their neighbouring images in the archive. This may be helpful for possible later analyses.
Photographic fireball patrol
In case you want to operate a fireball patrol camera, you will need a wide angle lens, or even better, a fish eye lens. Depending on the conditions (moon, haze, city lights etc.) you may use medium-sensitive films (say, ISO 200/24) and expose for 1 to 6 hours. In the case of fireball patrol you should do as many observations as possible, even when the sky is partially cloudy, because bright fireballs are very rare events. Of course, such a patrol is most useful if organized in a kind of network with a number of participating stations separated by some tens of kilometers, like the European Network, because this allows to make measurements of the firebll trajectories and to determine the location in case of a possible meteorite fall. Details about the setup of a network and the analysis of double station photographs are also included in IMO’s Handbook for Meteor Observers.