Meteors are fine grains of dust that hit the atmosphere at great speed, burning up in a fraction of a second emitting a light of varying intensity and usually leaving no trace after the event.
So how do we going about capturing these events on camera? There are various techniques, all variations on the same theme, some involving sensitive video cameras and computer analysis and so on. But here’s a method that can be used by anyone with the following equipment:-
A camera with a shutter setting of several seconds or more
A remote shutter release
The camera need not be a DSLR as several advanced compact cameras and “bridge” cameras will have the required settings although may lack the remote release which is not essential as there is a workaround.
The approach to be taken is something of a scattergun approach – setting the camera up in such a way that if anything appears in a pre-determined area of sky it may be caught, then taking pictures continuously in the hope that something happens while the shutter is open. This can be done with film, and indeed many astrophotographers used to do this. The cost is considerable but sometimes worth it. My first and probably best meteor shot was a Perseid taken on film in 2004 (see below). It was frame 1 of 37 on a roll of film and the other 36 showed no more meteors, so the film and developing cost about £10. With digital photos costing no more than the cost of a small amount of electricity to charge the batteries plus a little bit of wear on the equipment, it is not uncommon for amateurs to take hundreds or even thousands of photos in a night looking for meteors!
Perseid Meteor image taken on film in 2004 – 30secs at f1.4 on ISO 400 print film with a 50mm lens on a Minolta SRT101 camera (cropped). (pic to follow)
This one was actually quite close to the radiant.
The camera needs to be mounted on a good tripod and pointed at an area away from the meteor radiant. The radiant is the part of the sky from which the meteors appear to emanate and there is usually a clue in the name. For example, the Perseids, in mid-August, appear to emanate from the radiant which is at the top end of the constellation Perseus, near the Double Cluster. In order to capture meteors, pointing the camera somewhere between 30 degrees and 60 degrees away from this area in pretty much any direction would be a good start. Upwards is generally good as the sky is at its darkest, but if observation is showing more meteors in a particular direction then it's a good idea to point the camera that way.
Here's the camera all set up and ready for shooting (pic to follow)
Generally the best choice will be a moderately wide-angle lens. The trade off here is that a narrower view will get a better picture of a meteor if one is caught, while casting the net wider makes a capture more likely but will give a smaller image. As with all astrophotography, zoom lenses can be used but they are optically more compromised with small apertures and complex constructions that lead to more internal reflections, so I prefer to use prime lenses if possible. I have two favourites for meteor photography – a 24mm f2.8 and a 50mm f1.7. With a fixed lens camera, set it to the widest angle setting. Focussing needs to be manually set to infinity – autofocus won't work on dark skies. Note that many modern lenses will actually focus a bit past infinity if fully rotated – this is to stop the AF mechanism hitting the endstop with a bang but it does mean that care is needed in setting the focus – any bright star will do, or a distant light will suffice as long as it's a fair distance away – a mile is plenty far enough.
The camera will need to be set to give continuous exposures and be fired from a cable release with a locking button. That way the camera can be set running and left alone leaving the observer free to watch the sky.
Exposure will depend on the prevailing lighting conditions – how much light pollution there is, whether the Moon is in the sky etc, so some experimentation is called for. A good starting point would be to take 10 second exposures with the lens wide open and the ISO set to 800 or 1600. If test exposures look dark, consider lengthening the exposures a bit more. Exposures of 10 seconds with wide lenses will have stationary stars, but as exposures become longer the stars will start to trail. The rule for this is t=600/f where f is the focal length of the lens and t is the longest exposure that will yield stationary stars. So for a 50mm lens, 12 secs is the max and for a 24mm, 25secs. Apart from keeping the stars still, settings like this will prevent skyglow from washing out the image except in very light polluted locations.
Other camera considerations – if the camera has built in noise reduction, turn this off, and likewise if the camera body or lens has a stabilising device, turn this off as well. The stabiliser is unnecessary with a tripod and can make the sensor hotter, hence noisier, and the inbuilt noise reduction will take additional blank exposures to be subtracted from the real exposure – Murphy’s Law says that the fireball you're hoping to catch will happen during this blank exposure!
Without a cable release, just keep firing the camera and if it has a 2 second self-timer use this as it will stop any vibration giving a wiggly effect on the stars.
Then it’s just a case of firing away for as long as either the darkness, the batteries or you manage to last!
Well then you have a card full of images to import into your computer and look at. Ideally this needs a piece of software that can whizz through the images quickly in full screen mode enabling you to see if you’ve caught a meteor. I find Faststone Image Viewer to be very good at this – indeed I use it as my standard viewer and it does much more than its name suggests, having a good few editing functions as well. http://www.faststone.org/ It’s free for personal use too!
If you have one or more meteors – well done – post your image on our forum, send it to Spaceweather.com and enjoy what you’ve learnt. Or, if you have a failure, think about taking 100-200 of your pictures and use the free Startrails software http://startrails.de/ to stick them together into a Startrail picture! The more adventurous still may want to import the pictures into a video editor and create a moving sky video which is good fun too.