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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 of electronic sensors very quickly. Other considerations for high speed photographers are record length, Reciprocity breakdown, and Spatial Resolution . EARLY APPLICATIONS 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. STROBOSCOPY AND LASER APPLICATIONS less than 1 millisecond after detonation. From the Tumbler-Snapper test series in Nevada, 1952. The fireball is about 20 meters in diameter in this shot. The spikes at the bottom of the fireball is known as the Rope Trick Effect .]] 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, this incredible photograph of an explosion using a Rapatronic Camera . Advancing the idea of the stroboscope, researchers began using lasers to stop high speed motion. 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), 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. Pin register
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.
Rotary mirror The 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 fps for a few hundred frames. 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, Schlieren Photography . VIDEO Early video cameras using tubes (such as the Vidicon ) suffered from severe "ghosting" due to the fact that the latent image on the phosphor remained even after the subject had moved. Furthermore, as the system scanned the phosphor, the motion of the scanning relative to the subject resulted in artifiacts that compromised the image. 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 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 fps. 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 fps), 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 fps 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 fps. CMOS The introduction of . Photobit eventually introduced a 500 fps 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 NAC, Photron, Weinberger, Olympus, Redlake, and others, with sensors developed by Photobit, Cypress, and in-house designers. 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. REFERENCES
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