Star Streaks
GALLERY
A fine exposure of the summer Milky Way. There is even a meteor trail.
Despite light pollution fro Norwich, the Andromeda Galaxy
shines through.
Another view from Norfolk
The best star streak photo yet, taken by a camera sat on a all under the clear, dark skies of La Palma
La Palma again, but here with a cloud lit by street lights
This is probably the easiest way to record astronomical data - and create fascinating pictures. the method not only records stars but also planet, nebulae, meteors, bright galaxies and satellites. Unfortunately it also records aircraft and light pollution.
The main aspect of the night sky that makes imaging difficult is that everything is so dim. The meagre amounts of light that reach us from stars makes normal film and digital photography impossible. The good news is that modern film is capable of recording both the colour of starlight and the glow of interstellar hydrogen clouds if it is exposed long enough. In fact for star colour, a star streak photo is usually better than a tracked exposure as the colours tend not to be burned out by over exposure.
EQUIPMENT
To record light from the night sky you need a manual Single lens reflex (SLR) camera. Although these are still made, most manufacturers have moved on to electrical everything. But the second-hand market is full of discarded manual cameras. You can pick up a decent camera from about £20 up. The only reason for paying more is to get a better lens. The camera needs a B setting to let you keep the shutter open and a manual cable release socket (a threaded hole) in the shutter button. Check the camera is manual by removing any batteries it may have for the meter and then press down the shutter button in the B setting. If the shutter stays open whilst you have your finger on the button it will be fine for long exposure photography. You'll also need a cable release which cost about £5 new. Another useful accessory is a skylight filter. This will protect your lens. Also if the lens dews up you can remove the filter and keep taking shots.
If you're given a choice of lenses go for the biggest aperture (smallest f stop). Wide angle lenses of 35mm or less will record a larger section of the sky. Telephoto lenses of 70mm plus are more suited for piggyback photography on a guided scope.
A sturdy tripod will allow you to take photographs more easily but it's not essential. My best photograph so far has been taken by the camera sitting on a low wall.
TAKING PHOTOS
We have used Kodak Royal 400. It is a fast film which is sensitive to the red light emitted by hydrogen nebulae and is good at recording star colour. It also has a relatively small grain size enabling it to record fine detail.
For a 2.8f lens we have found that a 5 minute exposure works well. For dark sites and wide angle lenses, a longer exposure will record nebulae and faint star field better.
It's very easy to make the camera shudder as you lay down or pick up the shutter release cable. This can be eliminated by cupping your hand over the lens as you release the shutter and let go of the cable. Do the same before you pick up the cable and close the shutter. Beware of light pollution reflection off your hand.
PROCESSING
Take your exposed film to a developer who will scan your images onto CDROM. In the UK, Boots the chemist do a good job - all ours are scanned by them. I always warn them that the shots are astronomical but I think the scanners just run automatically. The raw scans tend to have low contrast and light exposure which is good news as it records even the faintest of streaks from your negatives. It's then easy to adjust things with image processing software. I find that the histogram functions offer the best control.
Use a planetarium program like Starry Night or Distant
Suns to spot constellations and join op the centre of the streaks to put them on
a copy of your photo.
Planetarium programs
Distant Suns 4 (DS4) includes a very detailed astronomy manual. There are also tutorials in the main program. Two versions of DS4 can be downloaded. Only use the DS4 seti version if you want to install seti@home software from the internet to help search for extraterrestrial intelligence. http://www.distantsuns.com
Sky map Pro is what it says on the tin - a professional program that can even control a telescope! It should work with the school goto scopes. As about borrowing a computer extension lead if you want to have a go. http://www.skymap.com