Freezing time

Ever since Eadweard Muybridge's photographic studies of trotting and galloping horses in the 1870s proved that the horse is at moments fully airborne in both gaits, photography and film have been used to freeze time and capture moments that happen too quickly for us to directly observe.

Animation from frames taken from Eadweard Muybridge's Human and Animal Locomotion series, (plate 626, thoroughbred bay mare "Annie G." galloping) published 1887 by the University of Pennsylvania

Muybridge used a system of multiple cameras firing in sequence to capture these and his later motion studies of other animals and humans. (1)

In sports, camera systems have been used to adjudicate the outcomes of close races since as early as 1912.  Since the 1930s, a method called "strip" or "slit" photography has been used to capture race finishes; rather than capturing a full field of view at a single moment, it takes a continuous exposure as film moves past a narrow slit aperture.  This produces an image over time of all that happens at the finish line; stationary things appear as streaks, while racers each appear in side view as they pass the finish line. 


This method was first developed by Lorenzo Del Riccio in 1937, adapting technology that had earlier been used with a moving camera and stationary subject for panoramic photography to capture the finish of horse races with a stationary camera. (2) 
Later developments allowed the time to be recorded onto the photo strip, and eventually for the film to be developed within the camera, allowing the photo-finish results to be obtained much more quickly; there are now digital photo-finish systems using the same strip-exposure method. 

This photograph, courtesy of Microgate, was taken with their Photo-Finish Lynx system.

The strip-camera method helps us disambiguate things that happened quickly at one location by turning time into distance.  Other sorts of photography use very short exposures to capture single moments too short for our ordinary vision to perceive.  Harold Eugene "Doc" Edgerton of MIT developed the use of electronic strobe lights for photography, which in addition to everyday photography in lower light, can be used to illuminate a subject for a millisecond or a microsecond, making available to the camera, and sometimes even to the naked eye, events on those time scales. 
http://webmuseum.mit.edu/images/DIAmed/HEE-NC-36012.L.jpg
http://webmuseum.mit.edu/images/DIAmed/HEE-NC-59001.L.jpg

Hummingbird in flight, by H. E. Edgerton, courtesy of the Edgerton Digital Collection at MIT

Bullet piercing three balloons, by H. E. Edgerton, courtesy of the Edgerton Digital Collection at MIT

 Many technologies have been brought to bear to produce high-speed images.  Some produce multiple still images at a very high frame rate.  The basic cinema camera technology moves a continuous strip of film into place behind the shutter and stops it as the shutter opens.  This produces clear, sharp images, but the stress on the film from stopping and starting makes this approach impractical above about 500 frames per second.  In rotating-prism cameras, the film can advance continuously, and the speed of the prism's rotation is synchronized so that the image keeps pace with the film.  The images produced in this way are not as crisp, but depending on the number of facets in the prism, these cameras can reach a speed of 40,000 frames per second -- with a reduced frame size for the highest film speeds.  Beyond that speed, unsupported film is under too much stress even when moving continuously, and more complex systems involving film mounted inside a circular drum to support it, sometimes in combination with a system of a rotating mirror or prism and multiple lenses to convert a streaking image into frames.  The most sophisticated of these systems can achieve frame rates as high as 25 million frames per second -- but only for as many frames as will fit on the single loop of film in the drum.  Beyond a rate of 25 million fps, it is necessary to switch to electronic methods.  As of 2009, there were electronic image systems capable of capturing up to 100 million fps, and the technology continues to develop. 

Whatever technology is being used to capture the images, very short exposures require very intense light -- and even with a lower shutter speed, a camera can produce single short-exposure images, using a very brief intense flash of light on a subject otherwise in darkness.  Electronic flashes can be as short as a microsecond, electric sparks and x-ray flashes down to a nanosecond, and pulsed lasers as short as a picosecond.  As the time resolution of high-speed photography has increased, its uses have expanded beyond the investigation of human and animal movements into many areas of physics and engineering.  (3)

(1) "Freeze Frame: Eadward Muybridge's Photography of Motion", Michelle Anne Delaney, National Museum of American History, 2000 http://americanhistory.si.edu/muybridge/htm/htm_sec1/sec1.htm (retrieved 4/24/2013)
(2) "The Art of Strip Photography:  Making Still Images with a Moving Camera", Maarten Vanvolsem, Leuven University Press, 2011, p. 35
(3) Fuller, P. W. (2009). An introduction to high speed photography and photonics. Imaging Science Journal, 57(6), 293-302