Photons at Work   An optical setup to measure color dependent scattering in a glass cylinder. The light source that drives the setup is located in the lower blue box. Its output is fed through a fiber bundle to a collimator (the black cylinder in the center of the image), which produces a beam of parallel light. From here the light path goes through [1] an aperture to narrow the beam; [2] a mirror; [3] a dispersing prism to split the white light in its color components; [4] an aperture to suppress stray light; [5] two mirrors; [6] a pinhole to select a narrow color band; [7] a two lens beam expander; [8] a beam splitter cube; [9] the glass cylinder; [10] two detectors with a narrow field of view, both connected to an optical power meter that measures the ratio of the detector signals. A third (unused) detector looks at the second output of the beamsplitter. This scene was created as an experiment to combine a number of POV-Ray features: photons, dispersion, scattering media and radiosity. In this particular image the radiosity is set to zero, because it has little effect under the used lighting conditions. Apart from the ceiling lights that illuminate the room the POV-Ray scene contains only a single light source, located at the input of the collimator. Although it gives a good overview of the measurement setup, the above image is not really what I was after. To see the setup in proper operation the ceiling lights should be switched off, so that almost all illumination originates from radiosity. This produces a very nice image, but one with large brightness variations across the scene so that it can only be viewed in a reasonably dark room. Click here to view this image (the link attempts to use the full screen; if you do not like this, click here instead). For the best result your monitor should have a gamma of approximately 2.4 (as is used by the average PC). The fiber bundle and the coax cables in the scene are implemented as sphere_sweep objects. To aid in their design I wrote an Excel spreadsheet that can be downloaded here.

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