The following set of photographs illustrate the effect of the IDAS Light Pollution Suppression (LPS) filter. The general city glow is from San Diego. Nearby lights on the hillside are approximately 1/2 mile away.

In order to allow comparisons with minimal uncertainty about film, processing, and time of exposure, two cameras were used simultaneously to take filtered and unfiltered shots, then the filter was moved to the other camera and the procedure repeated. The photos are arranged so each horizontal pair is from one camera, and each vertical pair of photos was taken simultaneously.

Note the effect of the filters on the neighboring artificial lights as well as the distant glow of city lights.

Camera 1, Exposure 1 (no filter)	Camera 1, Exposure 2 (LPS filter)
Camera 2, Exposure 1 (LPS filter)	Camera 2, Exposure 2 (no filter)

Additional Technical Information

Both cameras were Nikon 35mm cameras with 50mm lenses set to f/4. Exposures were 15 minutes on Kodak PPF-400 negative film. Scanning was done on a Nikon LS-1000 35mm film scanner. Exposure was set by utilizing a "normal" reference negative and freezing the scanner settings for the scans of the four test photos. No additional contrast, brightness, or color balance adjustments were made to the scans.