Star Math

It was a really clear night on Saturday for another startrail test.  While I probably could have done without the lens flare, I really liked how clear the umbrella and tree foreground turned out.

In a given 24-hour cycle, the stars will rotate around the North Star a full 360 degrees.  That is, 15 degrees every hour.  I suppose you could leave your shutter open for a full hour with the bulb, but I’m guessing you’ll have let so much light in, you’ll be left with an entirely white exposure.

Instead, I find the easiest thing to do is a 30 second exposure with the intervalometer set to 35 seconds.  Then the aforementioned ImageMagick script or Photoshop action script will do the rest.

Below is essentially a composite 2-hour exposure:

35s intervals x 200 frames @ 10fps (about 2 hours)
[youtube:http://youtu.be/fKvIQ2Zdu_4%5D

Shutter=30s, Aperture=f/3.5, ISO200, 18mm

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2 thoughts on “Star Math

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