Rebel XT and Star Trails

[sundtracy]

Hello everyone, I am new here and hoping to get some help. We are going camping this weekend and I want to play with my new camera and star trails. I have the new Rebel XT, a remote and tripod...what do I do next? Is it possible? I have researched how to do it, but not much out there on digital so thought I would ask here.

Thanks!
Tracy

[lancea]

Far easier to get good results with a digital thanks to the wonderful sensitive sensors and immediate results! ;) Have a look here http://web.canon.jp/Imaging/astro/index-e.html. Also some examples here http://www.astropix.com/HTML/M_DAP/TOC_DAP.HTM.

[JakeC]

If we're talking 'star trails' then it's a little harder to get good results than with film. Reciprocity failure is about all that lets film down in this respect. Even the refined canon CMOS doesn't handle noise quite well enough to get long trails which usually require a 30-120min bulb exposure. Of course even with 10mins the sensor is getting very warm, so it wouldn't be something I'd like to put the camera through too regularrly. Then again that's what warranties are for :p

So digitally I'd be inclined to stack a number of 10 minute frames to simulate longer exposures. As for the shooting technique, put the camera into M> select Bulb for the shutter with an aperture as wide as allowable by the lens you're using then either focus on infinity or use the moon/a bright star to lock AF . If you'd like to include a foreground element go with something like F8 and focus hyperfocally, using a torch to grab focus at the correct distance. Obviously you need a steady tripid and a remote to trigger/hold the shutter open whilst in bulb mode.

For information on using Bulb mode check out your Canon users manual.

On stacking images: http://www.tawbaware.com/imgstack.htm
Hyperfocal Calculator: http://dfleming.ameranet.com/

I usually print out a hyperfocal graph for each of my lenses and carry them in my kit bag.