High-speed camera

A high speed camera is a device used for recording fast moving objects as a photographic image(s) onto a storage media. After recording, the images stored on the media 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 1000 frames per second into DRAM and playing slowly images back 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 billion 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 considerable 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 the interesting parts of what is 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 20,000,000,000 (twenty 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.

Uses in television

• The show Mythbusters prominently uses high speed cameras for measuring speed or height.
• Time Warp is 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.

Uses in science

High-speed cameras are frequently used in science in order to characterize events which happen too fast for traditional film speeds. Biomechanics employs such cameras to capture high-speed animal movements, such as jumping in frogs and insects, suction feeding in fish, and the strikes of mantis shrimp, using motion analysis of the resulting sequences from one or more cameras to characterize the motion in either 2-D or 3-D.

The move from film to digital technology has greatly reduced the difficulty in use of these technologies with unpredictable behaviors, specifically via the use of continuous recording and post-triggering. With film high-speed cameras, an investigator must start the film then attempt to entice the animal to perform the behavior in the short time before the film runs out, resulting in many useless sequences where the animal behaves too late or refuses. In modern digital high-speed cameras, the camera can simply record continuously as the investigator attempts to elicit the behavior, following which a trigger button will stop the recording and allow the investigator to save a given time interval prior to the trigger (determined by frame rate, image size and memory capacity during continuous recording). Most software allows saving only a subset of recorded frames, minimizing file size issues by eliminating useless frames before or after the sequence of interest. Such triggering can also be used to synchronize recording across multiple cameras.

Uses in industry

When moving from reactive maintenance to predictive maintenance, it is crucial that breakdowns are really understood. One of the basic analysis techniques is to use high-speed cameras in order to characterize events which happen too fast to see, eg. during production. Similar to in science, with a pre- or post- triggering capability, the camera can simply record continuously as the mechanic waits for the breakdown to happen, following which a trigger signal (internal or external) will stop the recording and allow the investigator to save a given time interval prior to the trigger (determined by frame rate, image size and memory capacity during continuous recording). Some software allows viewing the issues in real time, by displaying only a subset of recorded frames, minimizing file size and watch time issues by eliminating useless frames before or after the sequence of interest.

See also

• High speed photography
• Fastax (High speed camera)