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Tuesday, June 23, 2009

The Art Of Astrophotography


Capturing the heavens can be a rewarding and altogether unique form of outdoor photography

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Following in the tradition of his father, Galen Rowell, Tony Rowell has spent the last two years tracking the stars and planets to create his own celestial images. Rowell adds another dimension to his cosmic photos by using light-painting techniques to create a fusion of earth and space.
Over the past two years, I’ve used motordriven telescope mounts and various cameras to track the stars and planets in long single-frame exposures. I usually photograph around the new moon when the sky is the darkest, weather permitting. I joke with my friends that I’m putting in 9-5 days but my hours are 9:00 p.m. to 5:00 a.m. I frequent several high-elevation locations within an hour’s drive of Bishop in the Sierra and the White Mountains.

To add another dimension to the images, I’m using light-painting techniques that I learned from my father. I use flashlights and off-camera flashes to illuminate the subjects that I combine with the night skies in what I call “astro-scapes.” Some nights, I go out alone when my subject is a short walk from my car, but when my subjects require a long hike, I hire friends to help carry the 80-plus pounds of gear.

There are many methods you can use to take astrophotos of the cosmos. The easiest is to take wide-field exposures from a fixed tripod, which usually results in the stars trailing unless you keep your shutter open for 30 seconds or less with a 50mm lens or wider. Another technique is called piggyback photography, where you need to have a camera equipped with a Bulb setting and cable release to lock the shutter open. With our planet rotating 15º every hour, your camera has to be mounted on an equatorial telescope in order to track the planets and stars. The learning curve can be frustrating, and it requires many late nights to perfect the polar alignment (keeping the scope centered on the north celestial pole, which is near the north star, Polaris), but once you make it through what I call astro-boot camp, the images you’ll capture will be very rewarding.

One of the most popular techniques is prime-focus photography, which involves using a T-ring (an adapter that connects your camera to a telescope) so that you can take deep-sky photos of galaxies, nebulas and planets using your telescope as a telephoto lens. Photographers using film will have to bracket, while those using digital cameras have the advantage because they can figure out the correct exposure right away. Digital cameras are much easier to use because you can see relatively quickly whether you actually got the image you set out to create. Also, using film often requires a complex series of steps to make the film hypersensitive so the faint starlight will make an exposure. Digital cameras, which can operate at extremely high ISOs, give you a distinct edge. Many a film shooter has left a night of astrophotography only to find that none of the images came out, while digital photographers are able to evaluate and adjust and reshoot during the night. A few potential problems with prime-focus photography are vignetting in the corners of images and getting the focus just right.

For more advanced astrophotography, there are CCD (charge-coupled device) astronomical cameras that are specially designed for astro-shooting. These dedicated units have advantages over film and digital SLRs such as better light-gathering capabilities and increased sensitivity. However, astrophotography CCDs are expensive, and most of them have a very small field of view compared to film and many D-SLRs.

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