Tuesday, July 7, 2009

International Space Station (ISS) - Without Telescope

This might not look like much, but it's a view of the International Space Station pieced together from 19 photos taken without a telescope. I used my 500mm f/8 (fixed) catadioptric mirror lens, shooting at f/8, ISO800, 1/1500. Thanks to fyngyrz for the exposure info. It's important to realize that this is a sunlit - very bright - object, so we need the quick exposure.

The ISS travels at an average speed of 17,209 mph, completing 15.7 orbits a day. The orbit is very predictable, and using the charts at Heavens-Above, you can find out exactly when it will show up in your night sky. I was prepared for tonight's passing, having already manually focused on the moon with 10X live view, keeping the camera on tripod and pointed WSW, where tonight's transit would begin.

I found it very difficult tracking it with such a tight telephoto, keeping one eye outside the camera to help get it in my viewfinder. Once I narrowed it down, I led it by a full frame, parked the camera in the tripod's ballhead, and snapped away for the two seconds it would stay in frame before switching views to keep up. I took the cleanest shots at its peak of 57 degrees above the horizon.

I wasn't sure I had a single useable capture as I walked back from the shoot, but once I looked on the computer, I almost couldn't believe what I was seeing. A 10 megapixel photo will take up about 4 full monitors worth of screen real estate. When viewed at that full resolution, the ISS is much smaller than a fly - a little speck with three blobs - the space station and its two big solar panel arrays.

I took about 90 shots of the space station tonight, throwing away all but the best 20, then stacking (combining) them together in Lynkeos. Stacking several images of the same shot helps remove the random noise due to atmospheric distortion. After enlarging and correcting the white balance, this is the final result. Take a look at one of the raw shots to see what I mean - and keep in mind that I'm zoomed in at an effective 800mm (500mm x 1.6 crop factor) and the crop of just the space station.

Here's a tight crop of one of the unprocessed images to show what a difference the image stacking makes:

Canon 40D, Phoenix 500mm f/8 Mirror Lens
Bogen/Manfrotto 190XPROB Tripod Legs, 322RC2 Grip Action Ballhead

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