Tuesday, March 25, 2008

Crappy Space Station Photo

I now know I can do better, as this was not exactly thought out, but I figured I would post it anyway just to show that it can be done ... and to record the always awesome experience of seeing the space station and the shuttle go overhead. The photo was made on the spur of the moment. Technical nonsense is all below the fold. Click on the image to see all of it.

The squiggly lines are a sort-of-double exposure of the Space Station flying over our house tonight. It is really one very long exposure, but there are two tracks (and two trees and two power lines) because I moved the camera during the exposure.

Given the lighting conditions (there was a sodium vapor street light on the power pole that is in the lower left corner of the frame), this is actually quite amazing. This picture resulted from some significant tweaks of the Nikon raw image and has been resized by a factor of 4 from the original to save on disk space and bandwidth and to smear out the artifacts of a long exposure at low light levels.

We also saw the Space Shuttle, which was about 20 seconds behind, but did not even try to get a picture since (a) it was quite a bit dimmer and (b) I didn't think this one had turned out.

The original was a real hack photo, but I figured I'd post the mistakes in case anyone wants to learn from them. It was taken with a Nikon D70 and a 70 mm lens with aperture priority !! forcing it wide open at 4.5. As stated above, we were just out in the street around the corner from our house where we had a good view of the track, which was only 20-something degrees above the horizon. Unfortunately, the view through a gap in the trees was over a street light. Fortunately, the ISS is pretty bright and software can perform miracles.

Mistake 1: I completely forgot to bump up the ISO from 400. Not sure if that made it worse or better, given the original camera image below. I actually don't think I would change it to a higher setting unless I had a better sky (like we had for the lunar eclipse). Mistake 2: Using aperture priority. Little did I know that the exposure time would go to infinity in this case! The jiggles are because I kept my hand on it, figuring it would need to be fired again every few seconds. Nope. Stayed open. I moved the camera after 5 seconds or so (guessing, because there was nothing to see through the SLR), and finally realized that the only way to close the shutter would be to turn the camera off. Next time I will use the manual setting and find the remote so I can leave the stupid thing alone.

What worked: Post processing. The image above is the result of starting from the raw file (the NEF raw data from the digital sensors) and pushing the color temperature way down (to about 2300) and tweaking the tint about 20%, using the color of the tree leaves as a clue. (You can see a lot more color detail, and noise, in the 6 Mbyte version.) I had first tried the tungsten presets, but that was not enough to kill off the effect of the sodium vapor light illuminating the tree (and all the other ones polluting the city sky). This is quite an improvement over what the camera showed me in the preview window and dumped into the basic jpeg file:

Yeah, that is really horrible. Nothing but sodium yellow and a bunch of lines. Suprisingly, one can do almost as good as the raw file edit just by hitting the Auto Levels adjustment in Photoshop. That gave the result below, which really shows the doubly-exposed tree rather well but leaves the power line yellow from the street light and still shows the track of the space station.

Both of these pictures are tiny (reduced by a factor of 8 from the original) since they don't actually contain any additional information. They do, however, show that what looked like a dark sky isn't even close to being dark!

Closing comment.
When I say "always awesome", I mean just as awesome as when I saw Echo go overhead. When I called my parents to tell them that there were some really good ISS viewing opportunities this week, my Dad said "The first satellite I ever saw was Echo". Me too. I was standing right next to him at the time.

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