Stop-motion illuminator for centrifuges

The majority of laboratory centrifuges have no provisions for observation of 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 electronic stroboscopy. To implement the mechanical stroboscopy, a standard microscope illuminator with a diaphragm is attached to the wall of the centrifuge. Through a hole in the wall the illuminator projects a cone of light with 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 moment of intersection. Its content is observed through a magnifier on the cover 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 μs, which is many times shorter than the duration of a xenon-tube stroboscopic flash (10–20 μs). This is the main reason why industrial stroboscopes cannot be used for stop-motion illumination in a centrifuge.