[Omaroo (Chris Malikoff)]

I like these shots Mike. Well done!

Here's a copy of something I put up on a photographic forum a while ago. It lets you perform really short exposures - so in theory you shouldn't need to take darks. I think the package has been mentioned here somewhere before too.

If you try to emulate the old film camera method of photographing star trails using a digital SLR then you'll quickly come across the achilles heel of DSLR's - limited exposure time.

1) The battery drains pretty fast holding the shutter open for hours.

2) Even at low ISO's you'll start to get thermal noise very quickly - making shots of 5 minutes or more difficult to repair later on - unless you remember to take dark frames and subtract them later or run them through NoiseWare or similar software. This software will process your dark frames alongside your subs too, if you like.

3) You'll start to get the old amp glow happening in the corners. All DSLR's suffer this except some of the newest (40D for example, which turns the CCD amp off until after the exposure is made).

So - how do you take hours-worth of short, continuous images and string them together to form long trails that look continuous themselves?

Try this software. StarTrails lets you take dozens if not hundreds of exposures over a night and then, as JPEGs, lets you select them all and auto-magically combines them for you - remembering to average the background so that you don't blow it out.

http://www.startrails.de/html/software.html

This example is one I just took. It consisted of 10 exposures of 300 seconds (5 mins) each. The combines time of celestial rotation is 50 minutes. If I were serious I'd have set up the lappy and asked it to control the camera to take, say, a hundred of these 5 minute frames. I'd have chosen a site that gives me a foreground too - like a row of trees or a building, for interest.