Wednesday, March 26, 2008

Much Better ISS Photo

Learn from your mistakes! This photo was taken tonight as the International Space Station went overhead. Two other pictures and a detail frame (explaining that the dashed effect at the start of the track is an artifact of manually releasing the shutter) are below the fold. Click the picture to see a larger version.

All photos were taken with speed set to ISO 200 (twilight sky is no longer so overexposed) and manual exposure for 10 seconds. The picture above was with the lens at 18 mm and f3.5 for two reasons: to wide the view to include the tree, and because it was really moving fast as it went overhead. Other than reducing the size by a factor of three, only modest Photoshop adjustments were needed to darken the sky.

An earlier picture, shown below, was made with the lens zoomed to 70 mm and f4.5.

The frame below, cropped from the original picture and shown without resizing, shows a detail of the dashed part of the track.

You can clearly see the spiral motion as the camera undergoes damped simple harmonic motion after I pressed the shutter and let go of the camera. Final lesson is that I need to plan better and dig out the remote shutter release to get rid of that junk.

A later picture, shot with 18mm like the one at the top, shows the ISS heading for the horizon and the lovely urban landscape of power and cable TV wires.

Other technical details: There was no need to work from the raw files when processing these pictures. Other than resizing, the only thing I did was use the manual levels control in Photoshop to darken the sky and improve contrast. Moving it to about 0.70, which was near the bottom of the lowest histogram peak, gave what you see here. (Using autolevels would brighten the sky, making it look like daylight, as shown in one of the modifications to yesterday's single photograph.)

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