As many of you may have noticed, I've been doing a lot of composite shots lately - the reasoning is simple - I want you to see the stars! Screw the trails, who cares about that? I want bright stars in the background! Galaxies, nebulas, constellations, meteors, I want them all crisp and clear! I didn't travel 3 hours by car to see dim skies!
A simple explanation of the technique I'm using is that I take 2 photos for every composite image you see, one for the light art, and another for the background. I don't move my camera from the tripod - I just take 2 for every one, making sure to re-focus from rather close to near infinity, it's basically a type of HDR for light-painting.. Which I think camera manufacturers are going to implement eventually, but for now it's a bit of camera-hack.
My method is to first find the most picturesque location, bearing in mind where the stars look best. To do this, I use my eyes first, then I confirm where the constellations are with an app I've recently acquired called 'Sky Guide' (iphone app) which uses your GPS to identify constellations.
After I've found my spot, and taken a high-ISO shot (around F2.8, ISO 3200 for 15 sec) - stars and environment should be pretty bright. Then I begin the light-art process - for this, my settings are around F8, ISO 100, for as many seconds as needed (use bulb mode!). If you've done this right, you should see decent light art and everything else should be rather dark. After you've got a decent take, re-focus for the stars, and reset your ISO to around 3200 (like before - during your initial test-shot). Get a bright and sharp star-shot then combine the two images in post.
With photoshop, start with the base light art, then put the star-shot on top and select 'lighten' on the top image to sandwich your two shots into one - presto! From Darius Twin to Starius Twin.