A high-speed camera is a device capable of capturing moving images with exposures of less than 1/1,000 second or frame rates in excess of 250 fps. It is used for recording fast-moving objects as photographic images onto a storage medium. After recording, the images stored on the medium can be played back in slow motion. Early high-speed cameras used photographic film to record the high-speed events, but have been superseded by entirely electronic devices using an image sensor (e.g. a charge-coupled device (CCD) or a MOS active pixel sensor (ASP)), recording, typically, over 1,000 fps onto DRAM, to be played back slowly to study the motion for scientific study of transient phenomena.
Overview
A high-speed camera can be classified as: A high-speed film camera which records to film, A high-speed video camera which records to electronic memory, A high-speed framing camera which records images on multiple image planes or multiple locations on the same image plane (generally film or a network of CCD cameras), A high-speed streak camera which records a series of line-sized images to film or electronic memory.
A normal motion picture film is played back at 24 frames per second, while television uses 25 frames/s (PAL) or 29.97 frames/s (NTSC). High-speed film cameras can film up to a quarter of a million fps by running the film over a rotating prism or mirror instead of using a shutter, thus reducing the need for stopping and starting the film behind a shutter which would tear the film stock at such speeds. Using this technique one second of action can be stretched to more than ten minutes of playback time (super slow motion). High-speed video cameras are widely used for scientific research, military test and evaluation, and industry. Examples of industrial applications are filming a manufacturing line to better tune the machine, or in the car industry filming a crash test to investigate the effect on the crash dummy passengers and the automobile. Today, the digital high-speed camera has replaced the film camera used for Vehicle Impact Testing.
Television series such as MythBusters and Time Warp often use high-speed cameras to show their tests in slow motion. Saving the recorded high-speed images can be time-consuming because , consumer cameras have resolutions up to four megapixels with frame rates of over 1,000 per second which will record at a rate of 11 gigabytes per second. Technologically these cameras are very advanced, yet saving images requires use of slower standard video-computer interfaces. While recording is very fast, saving images is considerably slower. To reduce the storage space required and the time required for people to examine a recording, only the parts of an action which are of interest or relevance can be selected to film. When recording a cyclical process for industrial breakdown analysis, only the relevant part of each cycle is filmed.
A problem for high-speed cameras is the needed exposure for the film; very bright light is needed to be able to film at 40,000 fps, sometimes leading to the subject of examination being destroyed because of the heat of the lighting. Monochromatic (black and white) filming is sometimes used to reduce the light intensity required. Even higher speed imaging is possible using specialized electronic charge-coupled device (CCD) imaging systems, which can achieve speeds of over 25 million fps. These cameras, however, still use rotating mirrors, like their older film counterparts. Solid state cameras can achieve speeds of up to 10 million fps. All development in high-speed cameras is now focused on digital video cameras which have many operational and cost benefits over film cameras.
In 2010 researchers built a camera exposing each frame for two trillionths of a second (picoseconds), for an effective frame rate of half a trillion fps (femto-photography). Modern high-speed cameras operate by converting the incident light (photons) into a stream of electrons which are then deflected onto a photoanode, back into photons, which can then be recorded onto either film or CCD.
Uses in television
The show MythBusters prominently uses high-speed cameras for measuring speed or height. Time Warp was centered around the use of high-speed cameras to slow things down that are usually too fast to see with the naked eye. High-speed cameras are frequently used in television productions of many major sporting events for slow motion instant replays when normal slow motion is not slow enough, such as international Cricket matches.