High speed photography
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High Speed Photography is the science of taking pictures of very fast phenomena. In 1948, the Society of Motion Picture and Television Engineers (SMPTE) defined high-speed photography as any set of photographs captured by a camera capable of 128 frames per second or greater and of at least three consecutive frames.
In common usage, high speed photography may refer to either or both of the following meanings. The first is that the photograph itself may be taken in a way as to appear to freeze the motion, especially to reduce motion blur. The second is that a series of photographs may be taken at a high sampling frequency or frame rate. The first requires a sensor with good sensitivity and either a very good shuttering system or a very fast light. The second requires some means of capturing successive frames, either with a mechanical device or by moving data off electronic sensors very quickly.
Other considerations for high speed photographers are record length, reciprocity breakdown, and spatial resolution.
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[edit] Early applications and development
The first practical application of high-speed photography was Eadward Muybridge's 1878 investigation into whether horses' feet were actually all off the ground at once during a trot.
Bell Telephone Laboratories was one of the first customers for a camera developed by Eastman Kodak in the early 1930s. Bell used the system, which ran 16 mm film at 1000 frame/s and had a 100 foot load capacity, to study relay bounce. When Kodak declined to develop a higher speed version, Bell Labs developed it themselves, calling it the Fastax. The Fastax was capable of 5,000 frame/s. Bell eventually sold the camera design to Western Electric, who in turn sold it to the Wollensak Optical Company. Wollensak further improved the design to achieve 10,000 frame/s. Redlake Laboratories introduced another 16 mm rotating prism camera, the Hycam, in the early 1960s. Photo-Sonics developed several models of rotating prism cameras capable of running 35 mm and 70 mm film in the 1960s. Visible Solutions introduced the Photec IV 16 mm camera in the 1980s.
The D. B. Milliken company developed an intermittent, pin-registered, 16 mm camera for speeds of 400 frame/s in 1957. Mitchell, Redlake Laboratories, and Photo-Sonics eventually followed in the 1960s with a variety of 16, 35, and 70 mm intermittent cameras.
[edit] Stroboscopy and laser applications
Doc Edgerton is generally credited with pioneering the use of the stroboscope to freeze fast motion. He eventually helped found EG&G, which used some of Edgerton's methods to capture the physics of explosions required to detonate nuclear weapons. See, for example, the photograph of an explosion using a Rapatronic camera.
Advancing the idea of the stroboscope, researchers began using lasers to stop high speed motion.
[edit] High speed film cameras
As film and mechanical transports improved, the high-speed film camera became available for scientific research. Kodak eventually shifted its film from acetate base to Estar (Kodak's name for a Mylar-equivalent plastic), which enhanced the strength and allowed it to be pulled faster. The Estar was also more stable than acetate for more accurate measurement, and it was not as prone to fire.
Each film type is available in many load sizes. These may be cut down and placed in magazines for easier loading. A 1200 foot magazine is typically the longest available for the 35 mm and 70 mm cameras. A 400 foot magazine is typical for 16 mm cameras, though 1000 foot magazines are available. The images on 35 mm high speed film are typically rectangular with the long side between the sprocket holes instead of parallel to the edges as in standard photography. 16 mm and 70 mm images are typically square rather than rectangular. A list of ANSI formats and sizes is available.
[edit] Rotary prism
The rotary prism camera allowed higher frame rates without placing as much stress on the film or transport mechanism. The film moves smoothly past a rotating prism which is synchronized to the main film sprocket. Each revolution of the prism "paints" the same number of frames onto the film as there are faces on the prism. A shutter also improves the results by only opening as the prism faces are nearly parallel, and then closing again.
- 16 mm rotary prism - Redlake Hycam and Fastax cameras are capable of 10,000 frame/s with a full frame prism (4 facets), 20,000 frame/s with a half-frame kit, and 40,000 frame/s with a quarter-frame kit. Visible Solutions also makes the Photec IV.
- 35 mm rotary prism - Photo-Sonics 4C cameras are capable of 2,000 frame/s with a full frame prism (4 facets), 4,000 frame/s with a half-frame kit, and 8,000 frame/s with a half-frame kit.
- 70 mm rotary prism - Photo-Sonics 10B cameras are capable of 360 frame/s with a full frame prism (4 facets), and 720 frame/s with a half-frame kit.
[edit] Intermittent pin register
The intermittent pin register camera actually stops the film in the film gate while the photograph is being taken. In high speed photography, this requires a complex mechanism for keeping the film moving quickly through the camera from the supply reel, but then stopping it for imaging, and then starting it again to move it onto the takeup reel. In many cases, a loop is formed before and after the gate to create and then take up the slack. Pull-down claws grab the film and move it into place and then move it back out of the film gate after the exposure. Register pins secure the film while it is being exposed. In some cases, vacuum suction is used to keep the film, especially 35 mm and 70 mm film, flat so that the images are in focus across the entire frame.
- 16 mm pin register: D. B. Milliken Locam, capable of 500 frame/s; the design was eventually sold to Redlake. Photo-Sonics built a 16 mm pin-registered camera that was capable of 1000 frame/s, but eventually removed it from the market.
- 35 mm pin register: Early cameras included the Mitchell 35 mm. Photo-Sonics won an Academy Award for Technical Achievement for the 4ER in 1988. The 4E is capable of 360 frame/s.
- 70 mm pin register: Cameras include a model made by Hulcher, and Photo-Sonics 10A and 10R cameras, capable of 125 frame/s.
[edit] Rotary mirror
The Cordin Dynafax held a strip of film still while a mirror rotated at high speeds. At the appropriate moment, the capping shutter was opened and the mirror steered images onto the film. This type of system was capable of 1,000,000 frame/s for a few hundred frames.
[edit] Streak, shadowgraph, and motion compensation photography
By removing the prism from the rotary prism cameras, and using a very narrow slit in place of the shutter, it is possible to take images whose exposure is proportional to the film speed across the slit. The image that results has several useful properties. The film advance direction is essentially a measure of time. If the subject's motion is perpendicular to the slit, it may show growth or motion perpendicular to the slit.
When the motion of the film is opposite to that of the subject with an inverting (positive) lens, and synchronized appropriately, the images show events as a function of time. Objects remaining motionless show up as streaks. This is the technique used for finish line photographs. At no time is it possible to take a still photograph that duplicates the results of a finish line photograph taken with this method. A still is a photograph in time, a streak photograph is a photograph of time.
By combining this technique with a diffracted wavefront of light, as by a knife-edge, it is possible to take photographs of phase perturbations within a homogeneous media. For example, it is possible to capture shockwaves of bullets and other high-speed objects. See, for example, Shadowgraph and Schlieren photography.
[edit] Video
Early video cameras using tubes (such as the Vidicon) suffered from severe "ghosting" due to the fact that the latent image on the target remained even after the subject had moved. Furthermore, as the system scanned the target, the motion of the scanning relative to the subject resulted in artifacts that compromised the image. The target in Vidicon type camera tubes can be made of various photoconductive chemicals such as Sb2S3, PbO, and others with various image "stick" properties. The Farnsworth Image Dissector did not suffer from image "stick" of the type Vidicons exhibit, and so related special Image Converter tubes might be used to capture short frame sequences at very high speed.
The mechanical shutter, invented by Pat Keller et al at China Lake in the 1980s, helped freeze the action and eliminate ghosting. This was a mechanical shutter similar to the one used in high speed film cameras, a disk with a wedge removed. The opening was synchronized to the frame rate, and the size of the opening was proportional to the integration or shutter time. By making the opening very small, the motion could be stopped.
Despite these improvements in the image quality, the systems were still limited to 60 frame/s.
[edit] CCD
The introduction of the CCD revolutionized high speed photography in the 1980s. The staring array configuration of the sensor eliminated the scanning artifacts. Precise control of the integration time replaced the use of the mechanical shutter. However, the CCD architecture limited the rate at which images could be read off of the sensor. Most of these systems still ran at NTSC rates (approximately 60 frame/s), but some, especially those built by the Kodak Spin Physics group, ran faster and recorded onto specially constructed video tape cassettes. Eventually, the Kodak group managed to develop the HG2000, a camera that could run at 1000 frame/s with a 512 x 384 pixel sensor for 2s.
By adding an image intensifier to a CCD, it is possible to capture a single frame of a very fast event. Hadland uses this technique for a range of high speed cameras capable of running at 1,000,000 frame/s, though record lengths are limited to 8 or 16 images.
[edit] CMOS
The introduction of CMOS sensor technology again revolutionized high speed photography in the late 1990s and serves as a classic example of a disruptive technology. Based on the same materials as computer memory, the CMOS process was cheaper to build than CCD and easier to integrate with on-chip memory and processing functions, though the image quality and quantum efficiency of CCD still compare favorably. The first patent of an Active Pixel Sensor (APS), submitted by JPL's Eric Fossum, led to the spin-off of Photobit, which was eventually bought by Micron Technology. However, Photobit's first interest was in the standard video market; the first high speed CMOS system was brought to market by Vision Research. Their Phantom v4 camera, with a sensor designed at the Belgian Interuniversity Microelectronics Center (IMEC), quickly made inroads into the 16 mm high speed film camera market despite resolution and record times (0.25 Mpixel, 4 s at full frame and 1000 frame/s) that suffered in comparison to existing film systems. IMEC later spun the design group off as FillFactory, which was later purchased by Cypress Semiconductor. Photobit eventually introduced a 500 frame/s 1.3 Mpixel sensor, a device found in many low-end (high speed) systems.
Subsequently, several camera manufacturers compete in the high speed digital video market, including Fastec Imaging, NAC, Photron, Weinberger, Olympus, Redlake, and others, with sensors developed by Photobit, Cypress, and in-house designers.
In addition to those science and engineering types of cameras, an entire industry has been built up around industrial machine vision systems and requirements. The major application has been for high speed manufacturing. A system typically consists of a camera, a frame grabber, a processor, and communications and recording systems to document or control the manufacturing process.
[edit] Infrared
High speed infrared photography has become possible with the introduction of the Amber Radiance, and later the Indigo Phoenix. Amber was purchased by Raytheon, the Amber design team left and formed Indigo, and Indigo is now owned by FLIR Systems. Santa Barbara Focal Plane, CEDIP, and Electrophysics have also introduced high speed infrared systems.
[edit] References
- Edgerton, Harold E., and Killian, James R. (1939). Flash!: Seeing the Unseen By Ultra High-speed Photography. ASIN B00085INJ.
- Edgerton, Harold E. (1987). Electronic flash, strobe, 3rd Ed. ISBN 0-262-55014-8.
- Pendley, Gil (July 2003). "High-Speed Imaging Technology; Yesterday, Today & Tomorrow". Proceedings of SPIE; 25th International Congress on High-Speed Photography and Photonics 4948: 110-113.
- Ray, S. F. (1997). High speed photography and photonics. Oxford, UK: Focal Press.
- Settles, G. S. (2001). Schlieren and shadowgraph techniques: Visualizing phenomena in transparent media. Berlin: Springer-Verlag. ISBN 3-540-66155-7.
[edit] See also
- High speed camera
- slow motion (less advanced than high speed photography)
[edit] External links
- David Alciatore's collection of high speed video clips
- Andrew Davidhazy's collection of streak photography applications, overview of high speed imaging, and High Speed 101
- A history of early (19th century) high speed photography by Lincoln Endelman
- OSA - The Optical Society of America
- SPIE - The Society of Photo-Instrumentation Engineers
- IMEC - a Belgian research consortium
- http://www.mne.psu.edu/PSGDL The Penn State University Gas Dynamics Lab, showing high-speed schlieren and shadowgraph imaging research
- Liquid Art - High speed photography as art. A collection of droplet photos
