A catadioptric camera for ultra-violet spark photography

In order to perform "time-resolved" photography of long sparks on a strip of film placed inside a flywheel rim, an optical system has been devised based on a nearly concentric mirror-pair similar to that used in a conventional reflecting microscope. A field-flattening lens is used together with two lenses to correct the chromatic defects introduced by the field-flattener. The nominal aperture is f /1.85 with a focal length of 72 mm. Simultaneous photographs of the same discharge are shown taken by a f /4.5 quartz-rocksalt achromat and the system described above. These show the advantage to be gained by using the above system.