Sunday, October 23, 2011

Where the stars are...

Climbing is training, so that will be an ongoing thing. Now I have something of a base understanding of where I am, and some idea of the holes in my abilities. I'll work on those, and then check back in with the climbing gym a few times between now and the trip to judge my progress and latest weaknesses.

Taking pictures of the sky is complicated. Three major problems:
  • It's dark. Dark things are hard to photograph. This requires extreme sensitivity, extreme light gathering ability, or extreme gathering time on the part of the camera. Generally a good mix of all three.
  • We are on a big moving thing, and so if you plant your camera firmly on the ground the sky slowly shifts during the course of a long exposure. The higher the magnification the more noticeable this is for any given exposure time.
  • Light pollution sucks, and so does being at sea level for the purpose of this. Where I am there is 32 feet of water above me filtering out a great deal of starlight. This makes things darker to start with, less stable as the atmosphere shifts about, and plenty of material for the light pollution of my nearby city to muddle up.
To get the hang of things I started out by putting my trusty D90 on a firm tripod to toy with exposures and settings. Things of note:
  • With a 300mm telephoto lens an exposure of more than about 4 seconds turns the stars in to streaks. With an 11mm wide angle this takes more than 15 seconds.
  • higher ISO (light sensitivity) can be great, but it also has some flaws. This drives the sensor harder, and the result is more camera noise and grain for a given exposure length.
  • At some point you've gathered enough light that the light pollution becomes a dominant effect and longer exposures or higher sensitivity are only detrimental.
Results? Here's the result of a 15 second exposure at F2.8, ISO 500 using a Tokina 11-16mm wide angle lens. Color correction done in Lightroom, otherwise the processing is minimal:

Clouds didn't help, but that's Jupiter toward the bottom shining bright. This was a productive couple hours of practice and testing, but next up is taking this up a couple of notches...

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