An introduction to high speed photography and photonics

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1 The Imaging Science Journal ISSN: (Print) X (Online) Journal homepage: An introduction to high speed photography and photonics P W W Fuller To cite this article: P W W Fuller (2009) An introduction to high speed photography and photonics, The Imaging Science Journal, 57:6, , DOI: / X To link to this article: Published online: 18 Jul Submit your article to this journal Article views: 636 View related articles Citing articles: 8 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 25 December 2017, At: 18:34

2 293 An introduction to high speed photography and photonics P W W Fuller Guest Editor 1 INTRODUCTION This issue of the Imaging Science Journal is devoted largely to papers on the various uses of high speed photography and photonics. Although high speed photography is widely used in the scientific community, it may not be familiar to some readers. There have been many definitions put forward over time. One problem was that once the research advantages evident in high speed photography became apparent, the development of faster framing rates and shorter exposure times proceeded at a very fast pace. With the mistaken assumption that advances would not progress so far, so fast, region descriptions quickly outran normally used superlatives, thus resulting in a rather odd listing. One reasonable definition is contained in the Focal Encyclopedia of Photography, 4th Edition, (2007). 1 It divides the definition into four regions: (1) High Speed, 50 to 500 frames per second, using intermittent film motion and mechanical shuttering. (2) Very high speed, 500 to 100,000 frames per second, using continuously moving film, image compensation, and digital video systems. (3) Ultra high speed, 100,000 to 10 million frames per second, using a stationary film with moving image systems and electronically with image converter cameras. (4) Super high speed, in excess of 10 million frames per second, where film has been largely superseded by electronic imaging and recording. Currently, electronic imaging is commercially available up to 100 million frames per second (one must also remember that to achieve these framing rates, the shuttering exposure times must reduce accordingly). There are also some more simple word definitions which give the basic raison d etre of high speed photography. One of the neatest is defined by Paisley: 2 Recording optical or electro-optical information fast enough for an event to be evaluated with a temporal resolution which satisfies the experimenter. However, it is not sufficient to include only temporal resolution in framing rates or exposure duration, and we must also consider spatial resolution. These requirements must be balanced together to give the best solution to each problem. We can thus modify Paisley s definition slightly to: Recording optical or photo-optical information with adequately short exposures and fast enough framing rates for an event to be evaluated with a temporal and dimensional resolution which satisfies the experimenter. 3 Photonics is now coupled with high speed photography. It is felt that modern developments have introduced so many new forms of radiant energy to be used in the production of images of all kinds that their regular usage together should be acknowledged. Photonics is defined as The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The scope of high speed photography and photonics is very wide and new applications are appearing frequently. Some of the basic applications are listed in Table 1. One of the special capabilities of high speed cine photography is its unique ability to slow down or speed up an event record by simply changing the framing rate on playback. With this extremely useful attribute in scientific investigations, it has also become widely used in modern advertising on television and also in the making of cinema films where it is used with dramatic effect in action scenes. While high speed photography is often coupled with the idea of cine photography, i.e. using film or digital IMAG H3 # RPS 2009 DOI: / X The Imaging Science Journal Vol 57

3 294 P W W FULLER Table 1 List of applications for high speed photography and photonics Fluid flow and combustion research Ballistics and general armament research Manufacturing processes Sporting and physiological studies Lighting and electrical engineering research Astrophysics research Accident research Transport and vehicle research Atomic energy research Advertising and entertainment Aeroballistic Ranges Machining and tool design Physical and chemical processes Behaviour and movement of animals, birds and insects Medical research Space sciences research Racing timing Materials research Educational studies Wind tunnel research cameras to take a series of images, which when played back can give the illusion of motion. However, it can of course also describe the production of still photographs or chronophotography where the high speed aspect relates to the exposure times involved rather than the rate at which pictures are recorded. In this case, the images may be just individual productions to show a particular instant of time, or as in chronophotography they are taken in rapid sequence related to the rate of subject movement. They are then presented as a sheet of pictures in sequence together showing the event as one picture, requiring no need to be projected as in cine photography. Thus in the case of a simple uncomplicated subject, e.g. the analysis of a golfers swing, all the pictures may be superimposed on one another so that the path of the club can be clearly seen. An idea of the changing rate of swing can be seen by the changing distance between the sequential exposures of the club. Alternatively, if the subject is more complex and the exposures may overlap so that it is difficult to analyse the movement, a series of sequential pictures can be printed out on a common sheet as a chronophotograph, Lighting for such an experiment might be a multiple spark light source, a stroboscopic lamp or flash tube. 1.1 An abbreviated history of the development of high speed still and cine photography Only some of the highlights of progress to the present day are mentioned as the developments were spread over more than 150 years and a detailed description would require more than the limited space available. While the emphasis is on high speed photography, both ordinary still and cine are included in a minor way. This is because without developments in basic photography, e.g. new designs, emulsions and film stock, high speed systems would not have evolved. A listing of some of the books which cover the development in more detail is included at the end of this paper. The earliest recorded use of high speed photography was in the 1850s, when Talbot used a spark source to freeze the motion of a spinning disc on which a sheet of newsprint had been fastened. 4 Spark light sources had been available for some time, and until the production of the first cameras, scientists had used spark illumination in a very clever way to study short duration phenomena. This was achieved by quickly drawing the observed spark illuminated scene using the image retention ability of the eye. Strangely, Talbot s use of sparks was not followed up until some 20 years later. In 1858, Thomas Skaife, 5 an amateur photographer, took pictures of cannon balls in flight at Woolwich Arsenal, (on the Thames near London) using a barndoor camera which he had made. The shutter was in the form of two half doors with an overlap (hence the name) which were operated by elastic bands. This shutter had an exposure time of about one-fiftieth of a second. In the picture, the cannon balls have a faint smeared photo-trail due to the exposure time being too long. Because this was still very early in the development of photography and emulsions were very slow, sitters were used to having to stay still while a portrait was taken. As a consequence, he was asked many times How did you manage to stop the cannon ball while you took the picture?. The camera used by Skaife is on show in the Science Museum in London. Spark sources were used extensively in scientific research for still photography for the rest of the 1800s and into the 1900s. They are still a viable alternative to flash tubes or laser sources. In 1883, Mallard and Le Chatelier had made photographs of flames from explosions. Le Chatelier used a photographic plate dropping under gravity onto which the flame image was projected. This showed how The Imaging Science Journal Vol 57 IMAG H3 # RPS 2009

4 HIGH SPEED PHOTOGRAPHY AND PHOTONICS 295 the flames developed with time. This could be considered as a simple form of streak photography. By 1884, Ernst Mach, whose name is associated with Mach Number, was studying the flow around bullets in flight using spark photography in conjunction with a Schlieren system. In the process, he introduced many new spark circuit designs by which the bullets could trigger their own photographs. He had been led to study bullets in flight, after hearing a lecture on ballistics by the Belgium expert Meisen. Meisen had proposed that part of the damage caused by bullet impact was due to a parcel of high pressure gas which the bullet carried on its nose. By firing bullets through thin metal plates, Mach was able to show that the shock waves formed as a continuous process and they were reformed after exit from the plates. Later, Mach s son Ludwig joined him in his studies of flow patterns and improved the spark triggering systems. By 1892, Sir Charles Boys 6 in London followed the work of Mach by also taking pictures of bullets in flight. However, instead of using Schlieren systems as Mach had done, he changed to the much simpler shadowgraph system, which he found to give just as good results. He worked at one of the larger colleges in London and set up his range in a corridor. What Health and Safety would have said about this arrangement, if it had existed at that time, is hard to guess. Over the turn of the century (from the 1800s to the 1900s), many experimenters produced camera designs which were nearly cine but not quite, as they were storing the images on sheets of film. In 1892, the Prussian Armaments Test Centre developed a multi-camera system with 12 cameras in a vertical circle, shuttered by a revolving disc with vertical slits. The system produced 1000 frames per second (fps). This had been influenced by the work of Muybridge in California in the 1870s. Muybridge had used a line of cameras separately triggered in sequence. Eadweard Muybridge, 7,8 an Englishman who spent much of his adult life in the USA, had become famous for his work on multiple sequential camera studies of people and animals in motion. The framing rate of his sequential pictures was largely set by the subject s rate of motion. By the 1870s, Muybridge had improved his system s picture quality at all framing rates by producing shutter exposure times down to 1/1000 of a second. His results were often presented in chronographic form. Before he had been able to obtain roll film Etienne Jules, Marey 9 in France made a camera which resembled a rifle. His idea was to make a camera which could be easily handled to take pictures such as a bird in flight. The input lens was contained inside a tube which resembled the gun barrel. Behind the barrel was a circular box which housed a steadily revolving disc shutter driven by clockwork. It was designed to take 12 pictures. Mounted on the same axle, behind the shutter disc was a second disc with 12 square openings behind which were mounted 12 squares of film. This disc revolved intermittently and was stationary, while the disc shutters passed a window. By the time the next shutter had come round, a new film was stationary in place ready to be exposed. Joined to the rear of the box was a butt which completed the gun illusion. By 1890, Marey was able to film at a rate of 100 fps. He made many films of birds in flight and was able to show the sequence of wing motion. Previously, he had made a box camera on the same lines, but like the gun camera limited to chronophotography rather than cine. As soon as he was able to obtain roll film, he redesigned the box camera. He retained the revolving shutter disc, but was now able to install two spools which allowed the film to move intermittently from one spool to another behind the shutter. This set the design scene for early cine cameras. In the early 1920s, Dr G. Bull in France used a drum camera with a synchronized magneto-driven spark source to take multiple pictures of bullets in flight and the first studies of insects in flight showing their wing movements. By 1925, Karolus had succeeded in making Kerr s electro-optical polarizing discovery into a camera shutter. These were used in the Second World War to photograph atomic bomb tests. Kerr cell shutters have been largely superseded by fully electronic cameras. In 1925, P. P. Quayle (USA) resolved the controversy as to whether projectiles continued to accelerate after leaving the muzzle. Using multi-spark systems, he found that bullets continued to accelerate for up to 6 8 in. beyond the muzzle. In 1926, Jenkins produced a cine camera using a set of lenses fixed to a vertical circular disc which rotated at high speed. At one side in line with the path of the lenses, a vertical film moved at high speed. By equating the rotary velocity of the lenses with the linear velocity of the film, the incoming images were swept in turn onto the film to produce a string of still IMAG H3 # RPS 2009 The Imaging Science Journal Vol 57

5 296 P W W FULLER images. The camera used 35 mm film and achieved 3200 fps. Spinning the lenses was a difficult requirement due to the weight and power required. In 1939, a commercial camera was produced by the Vinten Co. giving 3000 fps and built on a formidable scale. It was brought up to speed via an Austin Seven gearbox, the operator having to change gear in steps. Operators described using the camera as a rather frightening experience. It was fairly quickly superseded by the rotating prism camera (see high speed cameras). It will have been obvious from the above that spark sources were the only sources suitable for short duration illumination until well into the 1900s. Many scientists were preoccupied with armament developments and needed the ability to freeze fast motion. As shutters improved, reasonably short exposures could be obtained using sparks or magnesium flash or a steady light source such as the sun or arc lamps. 1.2 The arrival of roll film The development of cine film cameras was really made possible and greatly assisted by the production of film in long strips and rolls. Previous available film and various emulsion bases were in sheet form which was hard to incorporate as part of the design for a cine camera. Some ingenious attempts were made but with no significant progress. George Eastman can be considered as a primary source in the production of film for cine cameras. He was born in 1854 and in his mid-twenties, he began experimenting with gelatin emulsions. In 1881, he went into partnership to form the Eastman Dry Plate Company. He experimented, among many others, to produce stripping film, using a paper base which was coated with collodion and then with emulsion. After exposure, development and fixing, the paper was stripped away leaving a negative on the collodion base. However, it was not quickly taken up by photographers. Eastman was unhappy with the progress of his stripping film and to boost business decided to make his own camera to use it. The new camera, the No. 1 Kodak, was sold preloaded and after use was returned to the factory for processing, much like the similar system in use today. He employed a chemist to experiment with film bases and they produced a nitrocellulose film base from Celluloid, (invented in 1861 by Alexander Parkes). However, the new base was rather thick and not very flexible. In 1888, John Carbutt persuaded a manufacturer to make much thinner sheets which could support the emulsion without paper backing. This film could also be made into long rolls and a new era of cine possibilities had begun. By 1902, Eastman was producing nearly 90% of the world s output of film. Nitrocellulose was highly inflammable and around 1930 was replaced by cellulose acetate film which was much safer. Nitrocellulose film had been independently invented and a patent was applied for in 1887 by the Rev Hannibal Goodwin. After a 12 year court battle with Eastman, Goodwin s successors were awarded five million dollars. In 1893, Thomas Alva Edison and W. Dickson were working together. Following discussions with Muybridge and William Friese Green, they built a new camera using film rolls cut to a width of 35 mm with four rectangular perforations (i.e. sprocket holes) per frame. The films taken using this camera were used in the Kinetoscope, also an Edison invention. The Kinetoscope was first shown in Chicago in It was a coin operated peepshow machine which could only be viewed by one person at a time. The viewer looked down through an aperture onto the image which was magnified by a lens and shuttered by a revolving disc. A light illuminated each frame as it came into view. This was the first commercially successful motion picture machine, but was not suitable for multiple viewing. This was to come in 1896 with a projector built by Robert Paul in London. In film projection, it was found necessary to project at 16 fps to avoid flicker so this was selected as an international standard for silent films. When sound films arrived in the 1920s, adequate sound quality needed a velocity exceeding 400 mm s 21, so a new standard of 24 fps was fixed. Around 1900, a large number of arbitrary film sizes had been produced and used. In 1909, at an International Conference, Edison s roll film width of 35 mm and perforation disposition was adopted as a general standard. Many people attempted to make cine cameras, but many designs were extremely complex and did not become accepted for general manufacture. In France, the Lumiere brothers, Auguste and Louis developed a camera with an intermittent movement operated by a claw mechanism which moved the film using the perforations by one frame at a time; a pioneering design still used today. The The Imaging Science Journal Vol 57 IMAG H3 # RPS 2009

6 HIGH SPEED PHOTOGRAPHY AND PHOTONICS 297 camera could be used as camera, printer and projector and was called the Cinematographe. Their camera was a success and critics praised the quality of the films produced. Their first public showings were in 1895 in Paris. From that time on, the quality of standard speed cine proceeded to improve and with the introduction of talking pictures later in the 1900s gradually evolved into the complex systems which we know today. In a similar way, high speed still and cine photography went on to increase its scope and framing rates to its often astonishing current capabilities. Before the introduction of roll film, many photographers attempted to produce sequences of images on sheet film. Muybridge and others used multiple cameras exposed in sequence each with their own shutters. This produced sequences of action but not in an easy form to show as a cine film but more suited to the making of chronophotographic records. 2 LIGHT SOURCES Light sources are an extremely important part of high speed still and cine work. Short exposure times require a great deal of light to ensure that adequate quality pictures can be obtained. A high speed photographer will tell you, You can never have too much light. Bright sunlight is very useful, and adequate for some systems, but it is often not available, particularly in the UK and even if it is, it moves with time and it may mean constantly checking your camera view point and ensuring that you will still obtain the information which is required. There are two main methods to obtain the pictures required. Either the exposure time will be controlled by the camera shutter with either a constant light source or a pulsed light in synchronisation with the opening of the shutter. Alternatively, the camera shutter can be left open and the exposure controlled by a light pulse or pulses, or another form of radiation. The latter system is not applicable unless the subject scene can be in darkness during the imaging period. The choice of subject illumination will be governed by the presence of natural illumination, the characteristics of the subject, the desired results, and the presence of suitable recording and triggering systems. Some subjects may be self luminous, e.g. explosions or flame studies, and may not need extra illumination. 2.1 Types of lighting for high speed photography High speed photography requires higher and higher light levels as exposure times reduce. Developments over time mean that current experimenters have a large variety of light sources from which to choose. These include those shown in Table 2, plus other more exotic ones which are not in regular use or are meant for specialist subjects. Future developments in LEDs may also produce suitable sources for both continuous and flash use. There are already LED sources commercially available for lower framing rate photographic use. At the present time, there are still some problems with the development of blue and white LEDs, whereby attempts to increase output cause lowering of the lumens per watt efficiency. However, this will doubtless be solved in the near future. 2.2 Fibre optics Any assistance in setting up a site for high speed photography is always welcome. If the subject is a fixture or very difficult to move or partly obstructed, to the extent that it may be difficult to place the required lighting source to illuminate the area of interest, fibre optics may be the answer. Fibre optics have become extremely important in setting up communication channels and in connecting parts of optical systems together, but they are also very helpful in getting light to areas which are difficult to access. Their flexibility and small cross-section, allows them to be placed to best advantage in difficult locations. With a suitable combination of lenses, couplings and positioning stands, it is possible to place the light where it is needed. Similarly, fibre optics with suitable attachments can be used to take images of the subject and convey it to the camera in use, e.g. regularly used Table 2 Types of lighting available for High Speed Photography Source Typical duration (s) Sunlight Continuous Tungsten filament lamps of various types Continuous Arc sources and gas discharge lamps Continuous Flash bulbs Electronic flash Argon bomb Electrical spark X-ray flash Pulsed laser Super radiant light sources IMAG H3 # RPS 2009 The Imaging Science Journal Vol 57

7 298 P W W FULLER in medical investigations. Again in locations where the subject may be destroyed during the experiment, a valuable well protected camera can be connected to the scene by a relatively cheap fibre optic which is an affordable loss. 2.3 A word of caution It should be noted that light and other forms of radiation sources used in high speed photography should be treated with care and caution. There is not only the obvious danger to eyesight, but also the possibility of burns and fire hazards. Particularly dangerous are lasers, X-rays, spark sources and sources with a high ultraviolet content. Some lasers may not have visible beams so warrant special care. 2.4 A note on electronic flash tube development In the second half of the twentieth century, a photographic pioneer, Dr Harold Edgerton, in the USA, invented a new short duration light source in the form of the flash tube. In his early career, he had worked on mercury arc rectifiers and had been interested in the brilliant light given off by the mercury vapour in the tubes. After much experimentation, he produced a series of flash tubes using various gases suitable for a variety of applications, particularly where spark sources were not appropriate. The tubes were of many types with different shapes and triggering designs. These became much used in high speed photography and with them, he made many outstanding pictures. A very well known one is an apple exploding as a bullet passes through it. The tubes are in steady use in all kinds of photography for both scientific research and general photography. They are a component built in or added as an attachment to all good quality cameras used by the public. 3 PRINCIPLE TYPES OF HIGH SPEED CINE CAMERAS The following listing briefly describes the main types of high speed cine systems by presenting them in increasing framing rate. 3.1 Intermittent action types ( fps) The basic type of cine film camera moves the film intermittently into the gate by a moving claw system. While stationary in the gate, the film is exposed and is then moved on to the next frame. This is a high quality picture process in terms of spatial resolution and picture steadiness because of the lack of motion, while the exposure occurs. In the high quality cameras of this type, retractable pins hold the film motionless while the exposure is being made. Unfortunately, after reaching speeds of about 500 fps, the film becomes too stressed and tends to fail, causing the limitation of framing rate. 3.2 Rotating prism cameras ( fps) Around 1930, Tuttle invented a system which allowed the film to be moved continuously through the camera, thus avoiding the stressed film problems of the intermittent cameras. He used a rotating prism with multiple facets, through which the image was passed to fall onto the moving film. By coupling the prism rotation rate and film movement rate, it was arranged that the swept image moved at the same speed as the film. By doubling or quadrupling the number of facets, the framing rate can be increased to fps (half height pictures), or to fps (quarter height pictures) or split frames per second. Resolution was not as good as intermittent cameras. By 1960, it had been improved by placing the prism on the sprocket drive shaft. The possibility of increasing the framing rate using more prism facets was very attractive, but reducing the height of the pictures meant that the writing area for the exposure became a narrower strip with each increase. This limited use to subjects which were naturally of this shape. Luckily for armament researchers, it was fine for studies of the trajectory of projectiles in flight. 3.3 Drum and rotating mirror cameras ( million pps) Beyond about quarter pictures per second, conventional film transport systems and materials have reached their limit. Higher framing rates are obtained by fixing a strip of film to the inside of a rotating drum revolving inside a light tight housing. Supported by the drum, the film can revolve to high speed without being stressed. Lenses inside the camera separate the incoming streak images into discreet pictures. Picture numbers are limited to one complete revolution of the drum or perhaps more if more than one track of pictures can be made on the film. An alternative system using a laser strobe to The Imaging Science Journal Vol 57 IMAG H3 # RPS 2009

8 HIGH SPEED PHOTOGRAPHY AND PHOTONICS 299 illuminate the subject can increase the basic pictures per second (pps) to pictures per second. To increase framing rates above pps, a rotating mirror or rotating prism camera is used. Light images from the primary lens are relayed onto the metal mirror spinning at revolutions per second. The very high spin rate calls for a special design where the mirror is fitted to a fluted conical turbine base which floats on a column of high pressure gas. This avoids the need for mechanical bearings. Reflected streak images from the mirror pass onto a bank of framing lenses which change the streak image to framed images, then onto an arc of stationary 35 mm film. Framing rates up to 25 million pps can be obtained. 3.4 Image converter cameras Image converter cameras bear some resemblance to cathode ray tubes but operate in a different manner. They were developed to provide electronic imaging of events by eliminating the problems of mechanical cameras, such as inertia, poor response to low light levels, friction and the physical forces required to generate high framing rates. Delays due to inertia also complicate synchronisation to ultrafast phenomena. The image converter consists of an evacuated tube with a transparent photocathode deposited on the input window and a phosphor screen at the output window. The incoming image produces photoelectrons which are accelerated to the phosphor screen by applying a high voltage between cathode and screen where the incoming image is visually replicated. Other electrodes within the envelope allow the triggering of the beam, its guidance and acceleration. Thus, a set of sequenced images can be arranged across and down the phosphor screen. Rates of 600 million pps can be achieved. The pictures on the output screen can be photographed or a digital readout system can be used. Because the image beam can be accelerated within the tube, low light images can be boosted at the exit phosphor screen. The Imacon 468 image converter camera can produce a framing rate of 100 million pps. 3.5 Pulsed X-ray imaging systems X-ray systems can produce very short output pulses and they make it possible to observe images obscured by smoke, dust and plasma. An X-ray intensifier can be used to provide visible wavelength images, which can be passed through an image converter and recorded by other conventional photographic systems. Still or cine images can be obtained. Obvious advantages are that events taking place in enclosed spaces can still be covered using X-rays powerful enough to pass through the covering material. 3.6 Video systems Video systems have become a prominent presence in the domestic field with modest framing rates which are quite adequate for requirements. However, video cameras, used for TV and cinema filming, need higher quality definition and sometimes higher framing rates. Their use in scientific research work is also well established with framing rates and definition far above that required for domestic uses. One important method of obtaining video images is to use a charge coupled device (CCD) chip, which is made up of a rectangular array of pixels, i.e. a contraction of (picture element), a small element of a scene, in which an average brightness value can be determined and can be used to represent that area in the whole scene). CCD chips were developed in the 1970s 1980s and they have been steadily developed to have more and more pixels to improve their definition and advances in their internal design to speed up framing rates. Over more than three decades the use of video in the scientific research areas has grown steadily. The assets of immediate playback, on screen analysis, reusability of tape and solid state storage and the comparatively low complexity of operation, are highly prized in the scientific area. With the introduction of solid state storage, it has become possible to vary framing rates during recording, making the best use of available memory. The problem with attaining high framing rates had been the necessity to download an image from the CCD chip and then reset it for the next image. The goal of higher and higher resolution has meant increasing the number of pixels available, which means greater difficulty in connecting them to the rest of the system. The CCD response itself is very fast and for a limited number of frames, still/video systems can record several images on a chip and these can be downloaded at leisure. Other developments such as fast download to memory built into the chip have also helped. New designs using complementary metal oxide semiconductor (CMOS) chips have also been introduced. Cameras are improving all the time and framing rates have been improved by reducing the number of IMAG H3 # RPS 2009 The Imaging Science Journal Vol 57

9 300 P W W FULLER pixels used per picture. Video system research and development is so fast that it is difficult to forecast what it will achieve in the near future. Currently, the Shimadzu Corporation has a video camera with image storage incorporated into the sensor chip. It has a framing rate up to 1 million fps with a resolution of pixel. Alternatively, the Photron Fastcam SA4 has a CMOS sensor giving 3600 fps at pixel or up to fps at reduced resolution. extra components. Many of the relatively simple still cameras can record final images for analysis, which have already been obtained with more complex systems. A short exposure time shuttering system can be used in front of the still camera with its shutter open for single exposures, or the still camera with open shutter can be combined with a pulsed short duration light source. Digital still cameras are very useful in this roll due to the instant check that can be made on the image quality and suitability. 3.7 Streak cameras In the descriptions of cameras listed so far, it has been assumed that the images produced will be in a static form, i.e. frozen in motion as a recognisable picture. There is another method of recording called streak photography in which the shutter remains open and access to the subject is continuous, i.e. there is no framing attempted. This means that there is no interval between frames in which the subject is usually unrecorded. In high speed events, it is possible that valuable information may be lost during that interval. For example, if a container full of explosive is being blown up, it will be possible using streak photography to continuously measure the expansion rate of the casing. Similarly, the rate at which a flame expands can be observed as a continuous process. In the direction of film movement, the image is blurred, but at right angles to film movement, the size or width of the object can be continuously monitored with high precision. Any sideways movement or loss of part of the original object can also be measured and timed by knowing the film velocity or having timing marks recorded at intervals along the film. Sometimes, the event can be monitored by two cameras with one streak and one framing side by side. Many cameras can be easily modified to become streak cameras by removing the shutters or an optical element which serves to provide the framing process. Streak photographs are initially somewhat difficult to read but with practice can be interpreted very well. 3.8 Still cameras Still cameras have not been listed as there is such a variety to choose from, and many modern cameras in the higher price ranges have shutter speeds up to 1/ of a second or beyond, so they will be able to take lower mid- range high speed images without 4 ABILITIES OF HIGH SPEED PHOTOGRAPHY With reference to the ultimate abilities of high speed photography systems, it is interesting to note that it is possible to photograph the motion and changes in light pulse wavefronts using holographic methods, e.g. the changes in a wavefront when it is arranged to reflect a small part of it elsewhere, by placing a small mirror to the side of the flight path. The subsequent separation and motion of both parts of the wavefront can be followed (velocity of light: km s 21 ). 10 Among many other examples, a series of light pulses has also been captured passing through a lens and being focused down to a point. 5 TRIGGER SYSTEMS Trigger systems are essential for some types of high speed photography, particularly when the event is self-initiated or when it is necessary to be away from the area of the event. It may also be necessary to allow a delay after the beginning of subject movement before starting filming. For high speed subjects, operator response time may be too slow to catch the action. Trigger systems may also include delay units to ensure that various parts of the recording system start to operate in a set sequence. For example, rotating prism cameras require a certain time to accelerate up to a set framing rate before recording. Thus delay units might be used to switch on the lighting system and then delay shutter opening until the correct film speed is reached. Types of trigger systems are split between direct and indirect detection methods. Here are some examples: N simply make or break contact switches N detection of radiation emitted by the subject or reflected from it The Imaging Science Journal Vol 57 IMAG H3 # RPS 2009

10 HIGH SPEED PHOTOGRAPHY AND PHOTONICS 301 N detection of the interruption of an external radiation source by the passage of the subject N detection of sound emitted by the subject N detection of local pressure changes or shock waves produced by the subject N detection of changes in electrical or magnetic fields due to the presence of the subject. 6 SUMMARY High speed photography and photonics are now well established and acknowledged as a vital part of the scientific research scene. They have made a huge difference in the progress of a wide variety of scientific investigations. Human beings have always had difficulties in understanding events of very short duration or which moved so fast that the unaided eye was unable to follow what was happening. In earlier times, they were mostly natural events, but as scientific studies began, man-made events and experiments posed the same difficulties. To fully understand an event or process, there has always been a fundamental need to measure, quantify and if possible, record it. To be unable to do this was limiting scientific advances. The invention of high speed photography began to offer the means to make such measurements, and was primarily used as a measurement tool for a long period. Later, it has become partly involved in art, entertainment and particularly in the making of cinema films and advertising, where slow motion effects are widely used. Now it has reached a situation where its capabilities extend from microscopic events to the study of nuclear explosions and new developments emerge steadily for future use. Before the invention of workable cine cameras, a link towards cine photography was made by moving into the production of multiple sequential single exposures using banks of cameras with sparks or ordinary ambient light. When cine photography became a practical reality, mainly by the invention of film in strip form, systems were produced to provide sparks synchronized with shutter opening. In the late 1800s and into the 1900s, new types of light sources were developed for both still and cine usage. By the 1900s, photography played an increasingly important role in all kinds of scientific research. By the mid-1900s, in industry, many problems with machine faults were solved by the use of high speed cine photography. The detailed motion of fast moving machine elements could be played back in slow motion and the faults or misalignments could be revealed and corrected. In the later half of the 1900s and early 2000s, the emergence of lasers and other light sources, fibre optics, image converters, electronic cameras of many types and the advance of digital techniques have brought a revolution in the imaging field. In the search to achieve the highest framing rates and the shortest exposure time, film cameras have been overtaken by electronic systems. For some time, film was still used extensively as digital image detectors were unable to match the resolution of fine grain films. However, as time has passed, electronic imaging has improved in resolution to such an extent that it is a strong challenge to film and will continue to improve. In many applications, digital imaging has many advantages over film. In scientific research in particular and with the current emphasis on the saving of time and money, the ability to see the results of research experiments in a very short time, relative to film, is an extremely strong argument to go digital. While film cameras are still used, research into the design improvement of super-high speed film cameras has ceased. In some very high performance systems, film has been replaced by digital chips as the recording medium. The mechanical system is retained, but digital recording gives the system a new lease of life with the additional advantages of quick results, and the avoidance of the chore of setting the film into the camera. Despite the advances of digital methods of recording, it is unlikely that the use of film will completely cease for some time; certainly it will be likely to survive in the domestic area. The capabilities of fine grain film emulsions are very impressive. However, some large companies have begun to limit film production and this may mean that supplies become harder to obtain. Some types of high speed camera will still need to use film because their original design was meant for film. We shall have to wait and see. 7 NOTE The limited number of papers in this special issue of the Imaging Science Journal illustrate only a tiny part of the huge range of usage of high speed photography and photonics. With the current pace of developments in the field, it is extremely difficult to even guess at IMAG H3 # RPS 2009 The Imaging Science Journal Vol 57

11 302 P W W FULLER what the future will bring. What is certain, however, is that high speed photography and photonics will continue to play an extremely important role in all kinds of future research and photographic image production in all areas. For those wishing to explore the current and future possibilities of high speed photography and photonics, it is suggested that Ref. 11 will provide an excellent and reasonably up-to-date means of enlightenment. To keep up to date on developments, the Proceedings of the International Congress on High Speed Photography and Photonics are published by SMPTE, SPIE and others, New York, 1954 onwards. Congresses and proceedings are usually at two year intervals. REFERENCES 1 Fuller, P. W. W. In Focal Encyclopedia of Photography, 2007, 4th edition, p. 539 (Focal Press, Woburn, MA). 2 Paisley, D. I. What constitutes high speed photography. OE Rep., 13 November Fuller, P. W. W. Aspects of high speed photography. J. Photogr. Sci., 1994, 42, 42 45, 67 71, , , , Anon. Sketches of eminent photographers, William Henry Fox Talbot. Br. J. Photogr., 1854, 11, Skaife, T. Instantaneous Photography, 1860 (H. S. Richardson, Greenwich, CT). 6 Boys, C. On electric spark photography. Nature, 1893, 47, , Muybridge, E. Animals in Motion, 1899 (Chapman & Hall, London). 8 Muybridge, E. The Human Figure in Motion, 1901 (Chapman & Hall, London). 9 Marey, E. J. Le vol des Oiseaux, 1883 (Masson, Paris). 10 Abramson, D. Light-in-flight recording high speed holographic motion pictures of ultrafast phenomena. Appl. Opt., 1983, 22, Ray, S. F. (Ed.). High Speed Photography and Photonics, 1997, 1st edition (Focal Press, Oxford); 2002, 2nd edition (SPIE, Bellingham, WA). FURTHER READING 1 Camm, D. The world s most powerful lamp for high speed photography. Proc. SPIE, 1992, 1801, Courtney-Pratt, J. A review of the methods of high speed photography. Rep. Prog. Phys., 1957, 20, Courtney-Pratt, J. Advances in high speed photography High Speed Photogr. Photon. Newslett., 1983, 3, Cranz, C. and Glatzel, B. Photographic recording of ballistic and other rapid phenomena with the aid of the quenched spark. Phys. Gesell, 1912, 14, Davidhazy, A. Applications of fast and slow streak recording cameras. Proc. SPIE, 1987, 832, Dubovik, A. The Photographic Recording of High Speed Processes, 1983 (John Wiley & Sons, New York). 7 Held, M. The advantage of simultaneous streak and framing records in the field of detonics. Proc. SPIE, 1358, Hyzer, W. Engineering and Scientific High Speed Photography, 1962 (Macmillan, New York). 9 Jamet, F. and Thomer, G. Flash Radiography, 1976 (Elsevier, New York). 10 Kerr, J. On a new relation between electricity and light. Philos. Mag., 1875, 1, Nebeker, S. Rotating mirror cameras. High Speed Photogr. Photon. Newslett., 1983, 3, Ray, S. (Ed.). High Speed Photography and Photonics, 1997 (Focal Press, Oxford). 13 Saxe, R. High Speed Photography, 1966 (Focal Press, London). 14 Shoeberg, R. High-speed rotating prism cameras. High Speed Photogr. Photon. Newslett., 1983, Aug., The Imaging Science Journal Vol 57 IMAG H3 # RPS 2009