Friday, October 18, 2013

Blurry Star Trails Reveal True Star Colors

true star color blur
192 frames stacked in StarStaX, 300mm, f/13, 30 sec, ISO 1600

Intentionally blurry star trails show a greater contrast in true star color. The amber stars have cooler surface temperatures, and the white and blue stars are much hotter. The segments are the distance stars appear to travel in 30 seconds, and the gaps occur as the Earth turns between consecutive photos.

I left my focus intentionally blurry to average the light and spread it out over more pixels in order to photograph the true color of the stars. If light is sharply focused into a point of just a few pixels, the RGBG Bayered sensor can change the apparent color based on the point it hits on the sensor rather than the actual color of the light. If you spread the light out over a larger area, this is less of a problem.

Oops, just realized I left the camera at f/13 which might explain why I had to crank the ISO up to 1600 to see any trails. I thought it was just because they were blurry they weren't showing up as well - but this explains it! No light getting through!

star trails and camera
Picture of a picture: 100 frames with my point and shoot looking up at the DSLR

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