A review of the methods of high-speed photography

The variety, range and precision of methods available for photographic recording of fast phenomena have been increasing rapidly. The capabilities of the newer techniques are considered, classifying them by the kind of record obtained. Streak records with drum cameras can give a time resolution of 10 −7 sec; rotating mirror cameras at present approach 10 −8 sec and may eventually achieve ¼ × 10 −9 sec; deflecting image converters may go much further. Single flashes of light, bright enough for silhouette recording, can be as short as 10 −8 sec, and for reflected-light recording 10 −7 sec for near objects, or 10 −6 sec for a field of view a metre square. Kerr cells can operate with an exposure of 10 −8 sec, and image converter tubes 10 −9 sec. Several pictures can easily be taken at short intervals superimposed on the one plate. Frames may be separated by intermittent film movement at rates less than 300 pictures per second (p.p.s.); or for speeds up to 10 4 p.p.s. by using continuously moving film and short exposures, or by using some form of image movement compensation where exposures are a significant proportion of the interframe interval. With smaller pictures of lower resolution, higher speeds are possible. For higher speeds still one uses effectively separate cameras exposed in succession by mechanical means (such as a rotating slotted disc) up to 10 5 p.p.s., by optical means (such as the use of a rotating mirror) up to 10 7 p.p.s., or by electronic means (such as phased shutters or phased spark sources) up to 10 7 p.p.s. Comparably high speeds with less elaborate equipment are made possible by image dissection. Simple dissection plates with clear lines or holes in an opaque ground allow recording rates of 10 5 to 10 6 p.p.s., but with low throughput of light. Using a rotating mirror camera to traverse the image elements rates of 10 8 p.p.s. have been achieved for brilliant objects. Dissection by means of lenticular plates allows in many cases a considerably greater throughput of light. Simple cameras are now available that can take 300 pictures at 250 000 p.p.s. Lenticular plate image dissection has been applied to cinemicrography so that similar series of 300 pictures can easily be taken at 10 5 p.p.s. at magnifications up to 2000 × . Alternatively, the use of fibre light guides for dissection allows long series of pictures of low resolution at 10 5 p.p.s. The combination of image dissection and deflecting image converter provides means for taking a series of 50 pictures at rates of the order of 10 9 p.p.s. Using one or another of these techniques, reasonable photographs may be taken of most macroscopic phenomena that are not too remote, though synchronization problems are sometimes of overriding significance. The difficulties are greater when the interest is in fine spatial detail. These problems are accentuated in cine-micrography where the image moves many times faster than the event. In such cases one must take advantage of the most advanced techniques, and there is urgent need for the continued development of better methods.