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Slihouette imaging system
Our SVP observation and motion analysis system rests on two orthogonally-oriented optical rails, with the observation aquarium placed at their intersection. The imaging optics on each rail consist of a far-red light emitting diode (LED) placed at the focal point of a 14.5 cm diameter biconvex collimating lens whose output passes through the aquarium. The use of a collimated beam prevents perspective distortion; clear, sharp shadows of any organism (even a small virtually transparent one) in the beam’s path are projected. Shadow images are collected by a lens attached to a 0.5 inch CCD sensor video camera and recorded using a S-VHS video tape recorder. The optical components on each rail are aligned using helium-neon lasers, which also allow the vertical viewing heights and orthogonal orientation of the two rails to be established precisely. The synchronously-recorded orthogonal views allow exact determination of the three-dimensional positions of particles which appear in both fields of view simultaneously.
The manner in which these images are analysed is described elsewhere (under the heading “motion analysis”).
The illumination system consists of a light intensity-controlled 1000-W Xenon arc lamp connected to an ultraviolet (UV, 280-400 nm)-visible liquid light guide. The light guide was coupled to the arc lamp housing using a lensing assembly. The projecting end of the light guide (placed directly above the observation aquarium) was outfitted with a lens assembly and a filter holder, allowing complete control over the intensity and spectral quality of light delivered in any given experiment.
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