High-speed Camera

A high-speed camera is a device used for recording fast-moving objects as a photographic image(s) onto a storage medium. After recording, the images stored on the medium can be played back in slow-motion. Early high-speed cameras used film to record the high-speed events, but today high-speed cameras are entirely electronic using either a charge-coupled device (CCD) or a CMOS active pixel sensor, recording typically over 1,000 frames per second into DRAM and playing images back slowly to study the motion for scientific study of transient phenomena. A high-speed camera can be classified as (1) a high-speed film camera that records to film, (2) a high-speed framing camera that records a short burst of images to film/digital still camera, a high-speed streak camera that records to film/digital memory or (3) a high-speed video camera recording to digital memory.

A normal motion picture is filmed and played back at 24 frames per second, while television uses 25 frames/s (PAL) or 29.97 frames/s (NTSC). High-speed cameras can film up to a quarter of a million frames per second 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 can stretch one second to more than ten minutes of playback time (super slow motion). The fastest cameras are generally in use in 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 the crash testing to better document the crash and what happens to the automobile and passengers during a crash. 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 the newest cameras today have resolutions up to four megapixels at record rates over 1000 frames per second, which means in one second you will have over 11 gigabytes of image data. 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. The fastest high-speed camera has the ability to take pictures at a speed of 200 million frames per second. One of the solutions to drive down the recorded data, or to minimize the required time to look at the images, is to pre-select only the parts which are interesting enough to film. During industrial breakdown analysis, cyclical filming focuses only on that part of the cycle which is interesting.

A problem for high-speed cameras is the needed exposure for the film, so one needs very bright light to be able to film at forty thousand frames per second sometimes leading to the subject of examination being destroyed because of the heat of the lighting. Monochromatic filming (black/white) is sometimes used to reduce the required amount of light. Even higher speed imaging is possible using specialized electronic charge-coupled device (CCD) imaging systems which can achieve speeds of up to or in excess of 25 million frames per second. All development in high-speed cameras is now focused on digital video cameras which have many operational and cost benefits over film cameras.

Recent advances in the form of image converter devices are able to provide temporal resolutions of less than fifty picoseconds, equivalent to over 20 billion frames per second. These instruments operate by converting the incident light (consisting of 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.