Wednesday, February 23, 2011

Happy (Star) trails

I've always wanted to shoot star trails, and the clear skies in Queenstown, New Zealand afforded me this opportunity. The problem is that with digital cameras, there's one drawback -- to take a really impressive star trail photo, you need to leave the shutter open for several hours. However, with DSLRs, taking long night exposures is a two-fold problem -- long exposures heat up the image sensor quite a bit, and consequently results in noise, and on top of that, running the sensor that long, you risk the sensor being damaged from the heat. With the new Nikon D7000, I decided to risk it and leave the shutter open for a maximum of 10mins at f/8, ISO320. Ten minutes is all I dare -- my thinking is that the D7000 can shoot video for 20mins in one go, but with still images the camera needs an equal amount of time for its Long Exposure Noise reduction which uses dark frame subtraction (essentially the camera shoots the actual exposure, then closes the shutter and shoots another exposure of the same duration and removes noise from the first image by comparing the two shots in-camera). What this means is that for a 10min exposure, the camera's sensor is essentially running for 20mins. Contrary to what it looks like in this photo, the landscape was in almost total darkness and I could only focus by manually focussing the lens to infinity. Nikon D7000, AF-S Nikkor 12-24mm f/4.

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