Stop-motion illuminator for centrifuges

The majority of laboratory centrifuges have no provisions for observation o f the process of sedimentation and fractionation which goes on in the test tube in the darkness of a "black box." Some centrifuges have a transparent cover or a magnifier in the cover to watch a blurred picture of the layers in the moving test tube which provides little information. The stop-motion effect with the test tube can a priori be based on either mechanical or ele ctronic stroboscopy. To implement the mechanical stroboscopy, a standard mi croscope illuminator with a diaphragm is attached to the wall of the centri fuge. Through a hole in the wall the illuminator projects a cone of light w ith the diameter 0.1 mm at the top of the cone. The cone intersects with a 0.1 mm hole in the test-tube holder. The test tube is illuminated at the mo ment of intersection. Its content is observed through a magnifier on the co ver of the centrifuge. The holder has a cut-out window to see the test tube . The flash at the hole-beam intersection is 0.5 mu s, which is many times shorter than the duration of a xenon-tube stroboscopic flash (10-20 mu s). This is the main reason why industrial stroboscopes cannot be used for stop -motion illumination in a centrifuge. (C) 1999 American Institute of Physic s. [S0034-6748(99)04311-7].