Time Lapse Prism Projection Images

These images are composites of a sequence of pictures of my office wall. I had set a couple of prisms on my windowsill, and found that they projected very nice spectra onto the opposite wall, particularly when the window's blackout shade is lowered to just above the prisms. The larger projection is from a 6″ right-angle prism with its hypotenuse facing approximately up. The short projection is from a 1″ right-angle prism sitting on one of its short faces, with the hypotenuse facing up and into the room. Throughout the day, as the sun moves, their projections move in the same direction horizontally but in opposite directions vertically.

I took the time-lapse images by setting my DSC-P200 in its dock and placing it near the window. The camera has no time-lapse capability built-in, but the dock can be set to take a picture every 5, 30, or 60 minutes. Unfortunately it will not take an indefinite sequence of pictures, so I had to restart its sequencer once an hour. The pictures were taken from 10:50AM through 1:36PM on November 3rd 2007.

Each exposure was 1/500 second at f/2.8 and ISO 100. I composited the images by simply summing them, variously selecting all, every other, and every third image. In the case of the every-5-minutes sequence, the large projections overlapped and washed out, so I reduced the value component by 50% before summing.