Tuesday, September 21, 2010
The Guiding Light of Astro-Photography
I know nothing about astronomy, yet I find it often poking its head into my photographic world. Not only do both photographers and astronomers share an enthusiasm for optics and resolving power, both groups tend to place great importance on the night sky. The star-filled sky has been a subject of fascination for photographers since the birth of the medium, and with the modern advent of high-ISO, low-noise digital capture, I've seen more star-filled photos than ever before. Back in the days of film, short exposures that captured sharply focused stars weren't possible. Consequently, inventive photographers came up with star trails—the natural motion blur pattern that results from the rotation of our planet—making stars slowly arc their way through our camera frames. A lens pointed at the north star, and left open long enough to make a complete 180 degree rotation, will render a night sky filled with perfectly circular star trails. It's a great effect, and it's easy to achieve... but only if you know how to find the north star. I am not so star savvy, but I can usually point out the Big Dipper if pressured. It just so happens that's a great way to find the north star too. DPS recently published a piece by Peter West Carey specifically for photographers who want to find the north star. It’s a great tutorial, and I'd add to it this: use a map. If nothing else, download one of those fancy smartphone apps that lays out a star map over a real-time cameraphone image. Then simply set it and forget it, and watch those star trails form. Oh, one more thing: if you want to put this to good use you'd better get cracking. The north star will change position in 20,000 years and a whole new star will be closest to our north pole. Then you’ll probably have to download a different app.