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How to shoot the night stars

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July 10, 2004

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July 10, 2004

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July 12, 2004

http://www.fotoinfo.com/info/techniques/astroexposure.html

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July 12, 2004

The "circular look" you asked about are called "star trails."

If you aim at the North Star (in nothern hemisphere; South Star in southern hemisphere), it will remain "stationary" and the other stars around it will make a complete circle in approximately 24 hours. That's about 15 degrees of arc per hour (360 / 24 = 15).

How long an exposure must be to show star trails depends on focal length of lens as longer focal lengths magnify the view and therefore magnify the motion of the stars in the sky. It also varies by area of area of the sky you are photographing (how close it is to the pole star) and a little by your geographic latitude. For 35mm - 50mm focal lengths showing large expanse of sky, exposures must exceed about 30-45 seconds to show star trails. YMMV depending on focal length and area of sky you're aiming at.

If you want long star trails, plan on exposures measuring in hours! This requires dark sky; too much light pollution with too long an exposure will fog the sky and wash out the trails.

One of the best and most comprehensive books on the subject of astrophotography:
_Astrophotography_for_the_Amateur_ by Michael A. Covington.
http://www.covingtoninnovations.com/astro/

Most public libraries should have one.

-- John Lind

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July 12, 2004

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July 12, 2004

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July 12, 2004

	Wasatch Nightwatch II Film: Plus-X Pan Exposure: likely f/4, 2-3 minutes Mt. Olympus Salt Lake City, UT Climbed on top of my sister's house in the middle of the night to make this one. Late Fall, the mountain had some snow on its peak. Took several as the cloud cover was moving and continuously changing. I liked this one best with the clouds streaked from the long exposure. The white pinpoints in the clouds are not noise or artifacts. They're stars that peeked through breaks in the clouds for a number of seconds during the exposure; long enough for the film to record them, but not long enough to star-trail (from Earth rotation). John A. Lind

Most sources recommend starting with ISO 400, but this stuff is done using everything from ISO 25 to ISO 1600 films. There are many factors involved such as darkness of sky, how long an exposure you intend to make, focal length of lens, magnitude of stars you want in the photo, etc.

I suggest shooting some 100, 200 and 400 with a variety of focal lengths, lengths of exposures, etc., for each one to get a feel for these relationships and what works best for you.

BTW, my style of night shooting is not so much star trails as it is doing some constellations, smaller star clusters, and letting moon illuminate landscape. The one I've uploaded is the Wasatch Mountains from the roof of my sister's house on the outskirts of Salt Lake City. They're illuminated by the moonlight filtering through the cloud cover and the city lights. Used Plus-X Pan (ISO 125) with aperture likely f/4 and exposures on the order of 2-3 minutes. The pinpoints are too small to have survived the scanning; there are some stars peeking through the cloud cover and exposure was long enough for them to have trailed slightly.

Soooo . . . if it's not a dark sky night, you can do very long exposure landscapes too! (When you end up with lemons, make lemonade.)

-- John Lind

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July 12, 2004