Friday, April 22, 2011

Star Trails: Take #1-99

One final image from the La Fouly trip. I've wanted to do a shot like this for a while, but have always been put by the weather, cloud cover, technicalities of setting up my SLR to shoot so many consecutive frame, or, the big issue, not finding a good subject in daylight and figuring things out before it gets dark and cold.

The big issue above is quickly resolved by staying in a lovely chalet in the Swiss alps, scenery and subject are easily taken care off! I also realised that I could use CHDK again to over-ride the default limitations on my G9, and use the fortunately clear alpine skies to try a few things out.

I used a shutter speed override to get a 30sec exposure (G9 default is 15s) so that I didn't have to drop in to noisy iso800 territory. I used the 30s exposure with the Ultraintervalometer script to shoot one 30s exposure after another for as long as the battery held out.
1/99 frames

I managed to get 99 consecutive frames before the -5 cold claimed the battery. Back in the warmth I brought them into After Effects to create a short sequence showing the movement of the stars through the sky. This took a little more work than I though in AE as I had to bring one good frame to the front to give a consistently lit chalet throughout the animation (I knew this was going to happen as I'd wandered around with a manual flash filling in some light from different angles.) I also had to duplicate the star layers a few times to bring out the brightness in the final render. Frame rate is dropped to 15fps too as 99 frames isn't much to work with and the time stretching in AE wasn't giving the results I wanted. (*no reflection on AE here just my shoddy ability to use the tools!)




The animation is alright but, because of the lack of frames, it doesn't "do" much. I figured I should be able to get one still "Star Trail" image by combining all 99 frames into one still image.Rather than labouring through importing and layering 99 separate layers I used a custom photoshop droplet to open all the images into one file in Lighten Layer mode. (Thanks to TINYenormous for the quick tips on creating a droplet from an action, very handy) Again I duplicated the best lit chalet shot to the top of the stack and then masked back the sky to show the trails in the main image stack.

99x30second exposures.

As a first attempt at star trails, I'm pretty happy with this, especially considering it was all shot on a G9. Next time around I'll give it a go with the 20D and 10-22, that'll give me a much wider view and should make it easier to include the pole star.
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