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Tuesday, March 25, 2014

Solutions: Tracking The Sky

How to use a tracking mount to get phenomenal starry night photos with your DSLR

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A high ISO and open aperture can yield a beautiful Milky Way and landscape photo.

You can attach your DSLR to a tracking mount like the Vixen GP2 to get you into the possibilities of full-blown astrophotography.
The cooler winter months yield the best skies for pure astrophotography, but for most of us, long, cold nights spent sitting next to a camera with an open shutter really isn't all that appealing. Summer is the time when most of us are out in the places where our thoughts turn to photographing a starry sky. There are two fundamental kinds of "starscapes": star trails and photos that show stationary stars, usually with the long shape of the Milky Way stretching across the sky. We'll look at how you can do both, plus how you can take your stationary sky photography to the next level with a tracking mount.

Capturing star streaks is actually pretty easy. The most important things to have are a sturdy tripod and good technique. Star trails that rotate around a single point are aimed at polar north. This is the point around which the sky rotates. Note, when your goal is a big circle of star trails, you have to be pointed north if you're in the Northern hemisphere. Choose a wide-angle lens to capture a good amount of sky, as well as some of the Earth. You should be doing this on a night with little, if any, moon and no artificial light. You'll be shooting one very long exposure (or combining several long exposures), and your foreground will get blown out if the moon is up or artificial lights are on.

With the composition set, open your lens to its maximum aperture. If you need to stop down for depth of field, do so, but shoot at the maximum aperture you can. With a wide-angle lens, you really should be able to shoot wide open unless you're trying to include something quite close to the camera in the frame. Set the ISO at 100 and the shutter speed at B (Bulb). You need more than an hour to get the full effect of polar star trails. If your camera can't do a single exposure that long or if it creates excessive noise, you need to shoot a series of shorter exposures and combine them with software (DeepSkyStacker is a popular freeware option). You'll find that you probably need to experiment with ISO and aperture settings to get the stars to the brightness you want.

Aim north, anchor the camera firmly, and set an exposure around an hour at a low ISO to get star trails like this.
Photographing the Milky Way without any blurring is much easier with modern digital cameras than it ever has been before. The trick for showing stars sharply always has been to keep the exposure to less than 30 seconds. By boosting ISO to 6400 and shooting at a large aperture, you can get a good Milky Way image with some foreground. You need to experiment to see how your camera handles the noise at higher ISOs.

If you want to try to "see deeper" into the night sky, try working with a racking mount. Motorized mounts for large telescopes are expensive, but you can use a much smaller and less costly model for a DSLR. With this kind of setup, you can get a beautiful wide-field image. You won't be shooting with any terrestrial foreground when you're working this way. It's true astrophotography. What you will be able to do is shoot for longer than 30-second exposures while maintaining pinpoint stars. This allows you to use longer exposures that will, in turn, reveal fainter stars and other celestial objects.


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