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Twentieth Century Photographic Lighting - Introduction, Chemical Flash Lighting, Open Systems, Enclosed Flashbulbs, Duration and Synchronization, Modern Flashbulbs, Electronic Flash Lighting

time magnesium photography

JON TARRANT
Freelance Technical Journalist, Former editor of British Journal of Photography , Teaching faculty of Physics at Jersey College for Girls, Jersey, Channel Islands, UK

Introduction

Without light there can be no photography. The history of photographic lighting is therefore inexorably linked to the history of technology and most especially the development of a reliable and widespread electricity distribution system. Prior to the advent of electricity, artificial light was provided primarily by the combustion of oil, wax, tallow, or coal-gas. Even as late as the 1940s kerosene lamps were still being used for domestic lighting in rural parts of what would otherwise be considered to be some of the most developed areas of the world.

Although these light sources are sufficient to enable human vision they are not very actinic; they do not have a great effect on photographic emulsions. The “actinic value” is a measure introduced in Germany in 1941 by Otto Reeb to indicate the ratio between the lumen output of a standard daylight lamp and that of an artificial source when both produce a film density 0.1 above the normal fog level. This proved to be a rather problematic definition, not least because a UV source could produce the necessary film density without any visible light (and therefore zero lumens since the lumen is derived from the candela, which applies specifically to a precisely defined frequency of yellow light). Despite such difficulties, the qualitative idea of actinity as a qualitative indication of a light source’s photographic efficaciousness has stuck to this day.

The fact that the common artificial light sources proved poorly suited to photographic needs led 19th century photographers to look elsewhere for their sources of light. The most obvious recourse was to take all photographs using daylight, and studios were often designed with large north-facing windows that admitted a soft, shadow-free quality of natural light. Despite daylight’s effectiveness, convenience, and zero cost, it was not the ideal source simply because it was neither predictable nor controllable to the extent that photographers would have liked. Nevertheless, for most photographers—especially the growing band of enthusiastic amateurs—it was all that was available until well into the 20th century.

Professional photographers were served better as their fee-paying clients allowed them to explore new forms of artificial lighting that were effective with the film emulsions of that time. In particular, this meant a form of artificial lighting that was rich in near-UV light to which silver halide crystals are naturally sensitive. One solution came in the form of a soft gray metal called magnesium.

Chemical Flash Lighting

Open Systems

Sir Humphrey Davy first deduced the existence of magnesium in 1808, which was also the year in which he demonstrated the first electric arc light (see below). By coincidence magnesium was finally isolated by Alexandre Bussy in 1829—the year in which Davy died. Despite being metallic, a thin strip of magnesium ribbon is relatively easy to ignite and burns steadily with a bright white light. The first photographic applications of this observation were suggested in 1859 by English chemist and Photographic News editor William Crookes in response to a reader’s request for a method of lighting cave interiors. The first portrait taken using magnesium light is attributed to Alfred Brothers in 1864.

The first commercial magnesium burner for photography was manufactured by Edward Sonstadt’s Magnesium Metal Company in 1862. It used magnesium wire that was fed through an alcohol lamp to generate an intense white light of whatever duration was required to make the exposure. More rapid combustion of the magnesium, and therefore shorter exposure times, came with the invention of “blow-through” lamps that used a puff of air, provided by a pressed rubber bulb, to propel a cloud of magnesium powder into an alcohol flame. Exposures as short as one-tenth of a second were possible using devices of this type such as The Marion Economical Magnesium Flash Lamp and the Leisk Centrifugal Flash Lamp.

Inclusion of the word “economical” in the Marion’s model name was significant because magnesium was as expensive as silver at this time, thereby making efficient use of the resource a prime consideration. For even better results the puff of air could be replaced by a blast of pure oxygen, resulting in what must have been a near explosive flash of light.

Pure oxygen atmospheres were also employed in the early flashbulbs, but before they arrived flash powder underwent a process of evolution that saw the introduction of compound oxygen in powder form (as potassium perchlorate, for example) that was intimately mixed with the powdered magnesium before ignition. The most important initial work was undertaken by J. Traill Taylor, who was also an editor of the British Journal of Photography . Although Traill Taylor announced the first blended flash powder in 1865, the price of magnesium was still too high for it to find widespread use. It was to be another twenty years before this situation changed significantly.

Throughout this time those who could afford to use magnesium-based light sources also had to cope with the vast amount of white smoke that was produced in the form of magnesium oxide. It is only thanks to the fact that light travels considerably faster than smoke particles can diffuse through the air that it was feasible to take indoor portraits using magnesium powder. Various schemes were devised to cope with the smoke, ranging from assistants running around the room with fine fabric bags to capture the cloud, to elaborate ventilation systems coupled with remote powder ignition systems that delivered their light to the sitter through reflective or translucent surfaces. Clearly a more elegant solution was required.

A major step forward in smoke reduction was achieved by Adolf Mieche and Johannes Gaedicke in 1887. So successful was their flash powder formula, which used manganese peroxide as the oxidizing agent, that the product was marketed in Germany by Agfa for many years. Typically it required only about one gram of flash powder to make a successful exposure and the mixture could be ignited by a single spark rather than requiring a naked flame.

In the early years of the 20th century flash powder was common, albeit with improved formulations that reduced exposure times down to 1/100 of a second. Little improvement was either necessary or made to flash powder for the remainder of its useful life.

More important, all of the flash exposures made thus far (and many that were to follow) required photographers to use a technique wherein, owing to the somewhat unpredictable nature of combustion, the camera shutter had to be opened before the lighting system was triggered. The only alternative was to arrange the flash so that it would burn for an extended time at high brightness to allow the shutter to be opened and closed during the period of illumination, but this inevitably meant that not all of the light reached the film. Automatic synchronization was clearly impossible and there was a certain amount of compromise in early artificial light photographs as photographers endeavored to discover the best way of matching innovative lighting systems with the need for consistent operating procedures.

Enclosed Flashbulbs

To pick up the thread for the next line of development in magnesium-based artificial lighting it is necessary to return to 1893, when French diver and photographer Louis Boutan asked Monsieur Chauffour, an electrical engineer, to devise a way of providing artificial light underwater. Chauffour’s solution was to place a piece of magnesium ribbon in an oxygen environment inside a heavy glass jar, and to ignite the magnesium using electricity. The inevitable white smoke reduced the light output, and the heat and pressure generated by the reaction shattered many of these early flashbulbs, but the concept of a self-contained device was born. In 1925 Paul Vierkotter patented a flashbulb in which the atmosphere surrounding the magnesium was reduced to a near vacuum with just enough oxygen to react with the metal. By removing the 80 percent of the air that is inert nitrogen, Vierkotter was able to reduce the maximum pressure generated by the heat of the reaction, thereby reducing the likelihood of shattering. A further advantage was the ability to insert a greater volume of oxygen, thereby allowing the combustion of more magnesium than would otherwise have been oxidized. Typically the flashbulbs that followed contained about half an atmosphere of oxygen (which compares with approximately one-fifth of an atmosphere of oxygen in natural air).

Although Vierkotter demonstrated how to make a safe flashbulb it fell to fellow German Johannes Ostermeyer to develop the first commercial product, which was marketed by the firm of Hauff. Ostermeyer used the same basic design but replaced the magnesium with ultra-thin (half-micron) aluminum foil in a similar low-pressure oxygen atmosphere. The foil was ignited by a small filament that was coated with an explosive primer paste and heated to incandescence by a small battery. General Electric started manufacturing the Vierkotter/Ostermeyer flashbulb under license in England in 1929 using the Sashalite name which, owing its origin to top London celebrity photographer Sasha (born Alex Stewart in Edinburgh in 1892), appears to have been possibly the first instance of product endorsement in the photographic industry. Three years later, in 1932, Osram began manufacturing and marketing the same product under the Vacublitz name in Germany.

Early advertisements for the Sashalite flashbulb carried the slogan “Perfect pictures in your own home with safety and cleanliness,” making it clear that General Electric was aiming its new product at amateur photographers. The fitting at the base of the flashbulb was deliberately made the same as the fitting used in torches. This inspired move, and the fact that a mere 4.5 V was needed to fire the flashbulbs, enabled amateurs to experience flash photography with minimum of fuss and outlay. There were, however, disadvantages in the form of variable light output caused by the random arrangement of the foil inside the flashbulb.

A different approach was taken by the Dutch firm of Philips, which in 1930 introduced a flashbulb that generated light by the reaction of two gases: carbon disulfide vapor and nitrogen monoxide. Although this system was effective, the bulbs were very large and were subsequently replaced by another Philips innovation that addressed the problem of unpredictable foil arrangements inside the flashbulb. In 1932 the company developed an aluminum-magnesium alloy (93 percent Al, 7 percent Mg) that had high ductility and strength, which allowed very fine (32 µ) wires to be drawn at high speed on a commercial scale. The wires, which Philips called hydronalium, burned more evenly and consistently than did foil, thus opening the door to automated shutter synchronization, which had previously been impractical because of the unpredictable nature of early flashbulbs and flash powders before them.

Aluminum-magnesium wire flashbulbs quickly displaced foil types, but there was also a third design that employed metallic pastes. All flashbulbs used a paste primer that burned quickly and vigorously to ignite the wire or foil so it was a logical idea to experiment with all-paste designs. The mixture contained a reactive metal and an oxidizing agent that was surrounded by an oxygen atmosphere. Ignition was almost immediate, with a typical delay of less than 10ms, and was followed by rapid combustion that lasted for approximately the same time. The entire exposure was therefore initiated and completed in as little as d1/50 of a second with a very high degree of consistency.

Probably the most important flashbulb of all time was General Electric’s Midget #5, which broke with the previous convention of using an Edison screw mounting in favor of a new bayonet fixing. This in turn prompted a new generation of dedicated flashbulb holders and led to the Midget #5 becoming extremely popular with amateurs and professionals alike. (General Electric pulled off the same trick again in 1953 when its M2 miniature flashbulb introduced yet another base fitting and provoked a new round of more compact flashbulb holders.) In 1941, two years after its Midget #5, General Electric unveiled its Speed Midget flashbulb, which was the same size as its predecessor but offered a significantly faster burning time of just 1/200s.

This advance was a true advantage because by now cameras were being fitted with automated systems to open their shutters and trigger the flashbulb as a carefully timed sequence of events. The first camera to incorporate this feature (following a range of external accessories that had been offered previously) was the 1935 Ihagee Exacta Model B. In 1940 Kodak’s Six-20 Flash Brownie and Agfa’s Shur-Flash signaled the final demise of the open flash technique and with them brought easy-to-use flash photography to the masses.

It is worth noting that, despite its decline, magnesium ribbon was still used in its raw form as a slow-burning artificial light source during these pre-war years. In his 1938 book Life-like Portraiture , W. H. Doering includes the following technique for lighting with magnesium ribbon. “The main point to note is that after the ribbon is ignited it should be allowed to burn steadily for a small part of the exposure, after which it should be waived in a semi-circle in order to soften the shadows.” The book goes on to say that although photoflash bulbs had sufficient power for many uses flash powders were still the choice for most amateur photographers.

Duration and Synchronization

Flash powder continued to be manufactured until, and during, World War II (when it was used to illuminate the landscape for aerial photography) as flashbulbs became more and more reliable. The most significant safety advance was the addition of a tough lacquer inside the bulb to catch flying debris and another on the outside to protect users against the danger of shattering bulbs. This was complemented by an operational improvement in the form of a chemically active (cobalt salt) Blue Dot that turned pink if the flashbulb had leaked and was therefore defective.

So consistent did flashbulbs become that the American Standards Association (ASA) was able to introduce three categories that defined the light-time characteristics of different products: short peak (Type F), normal peak (Types M and S), or broad peak (Type FP). These characteristics were broken down into five time zones as follows:

  1. Contact time (the delay between electrical contact and the first appearance of light)
  2. Time-to-peak (the delay between electrical contact and maximum brilliance of the flashbulb)
  3. Flash duration (defined by the ASA as the time interval between 5 and 95 percent light emission)
  4. Time-at-half-peak (the time for which the flashbulb’s brilliance is above 50 percent of its maximum)
  5. Median time (the delay between electrical contact and the mid-point of the time-at-half-peak)

A number of characteristics can be deduced from these figures. If the flashbulb has an asymmetric distribution of light output with respect to time then the median time will not match the time-to-peak; the greater the time-at-half-peak value the longer the exposure time; the time-to-peak value is a practical indication of how quickly a picture may be taken after the flashbulb has been triggered.

The reason for the differences between flashbulbs, in addition to the differing combustion characteristics of foil, wire, and paste, was to accommodate different modes of automatic synchronized flash photography. Typically, a fast peak (Type F) flashbulb achieved its maximum output in no more than 10 ms, a medium peak (Type M) took just over 20 ms, a slow peak (Type S) took about 30 ms, and a broad peak (Type FP) burned at close to maximum output throughout 30-60 ms after triggering. Of these, FP flashbulbs gave out the most light over the longest time, whereas Type S achieved an even greater effect for a shorter period of time. Therefore, Type S flashbulbs were ideal for lens-shuttered cameras and Type FP flashbulbs were necessary when a focal plane shutter was used. It is for this reason that Type FP flashbulbs are so named when the names of the other three relate directly to their speed of achieving peak brightness.

Within each of these categories there existed a variety of different size flashbulbs with different light outputs to suit a range of applications, as indicated by Table 8.

Ironically, given the original need to produce chemical flash systems that produced a blue or UV-rich light sufficiently actinic to affect the relatively insensitive film emulsions of the early 20th century, later flashbulbs were sometimes deliberately designed to have a more red-rich spectral curve. The reason was a need to provide either good tone rendering in monochrome photography or accurate colors for those who were experimenting with newly available color emulsions. Considerable work was undertaken during the 1930s to determine both the lighting efficiency and the color temperature of different types of flashbulb fillings. Not surprisingly, given the practical experience of earlier years, aluminum was found to be a more efficient producer of light (in lumens per milligram) than magnesium, and an aluminum alloy containing about 7-8 percent magnesium was found to be better still. The color temperature of burning aluminum was found, by various workers, to range from 3500 K to about 4700 K compared with 3700 to 4000 K for magnesium: the Al 8 percent Mg alloy gave a color temperature of between 3800 and 4100 K. The problem is that none of these color temperatures matched either of the common color balances for color film, which is either around 5500 K for daylight photography or 3200-3400K for tungsten-light photography (which by this time had become very practical thanks to widespread electric lighting; see below). The solution, given the nearness of the lower color temperature, was to apply a colored layer to the flashbulbs to produce better color rendering when the lamps were used with tungsten-balanced film.

An even more extreme example of customized color output was provided by a variety of flashbulbs coated to absorb all visible light and emit only infrared light. These flashbulbs could only be used with infrared-sensitive films, of course, but still proved popular.

After World War II the only thing that still marred photographers’ experiences with flashbulb photography was an occasional failure caused by the low triggering voltage used, which was itself necessary to avoid using so large a battery that the flashbulb holder became unwieldy. The difficulty arose not from insufficient voltage to ignite the primer and fire the flashbulb, but rather from the build-up of tarnish or corrosion on the metal contacts that delivered the battery’s energy to the flashbulb. A greater voltage would overcome this problem but could not be allowed to hinder the handling and portability of the flashbulb holder. The answer was to install a capacitor in the circuit and to charge the capacitor from the battery before directing this accumulated energy, at a higher voltage, to the flashbulb. Using this method a 3V battery could become as effective as a 15-20 V supply—provided the photographer was prepared to wait while the capacitor charged up. This was not an unacceptable limitation when flashbulbs were handled one at a time, and had to be removed (carefully, as they were hot after firing) from the holder before a fresh bulb could be inserted, but it became less convenient when General Electric introduced its four-in-one Flashcube, which was let down by poor contacts. An ingenious, battery-free solution was devised by Sylvania for its Magicube system, which was fired by a sprung pin that acted on a miniature percussion cap.

Modern Flashbulbs

Although it is tempting to assume that flashbulbs are now a thing of the past, this is simply not true. In County Clare, Ireland, Meggaflash continues to manufacture flood, medium peak, and slow peak flashbulbs, as well as custom-made designs for specialist applications. According to the company’s Web site (http://www.meggaflash.com) there is a lead time on all flashbulbs: “We regret this delay in supply due to current demand.” So why do flashbulbs continue to be popular? Because, for their size, they offer more light output than any other portable source. Meggaflash’s PF330 flood flash, for example, can deliver an average level of 60,000 lumens for approximately two seconds, making it ideal for applications such as high-speed sequential photography.

Electronic Flash Lighting

Early Ambitions

Early experiments with flash lighting were far more concerned with observing high-speed events indiscernible by the unaided eye than they were with providing a source of illumination for photography. It is a fundamental failing of the human visual system that we cannot perceive as a distinct identity any event that exists in a continuous sequence of events. This means that when a piece of ceramic is broken by a hammer or an object falls into a pool of liquid we cannot see the initial fracture nor the size and distribution of the droplets that are thrown into the air, respectively. Nineteenth century scientists who were keen to learn about such things needed a way of observing these brief events: They noticed that individual raindrops were apparently frozen in the air by a flash of natural lightning and sought to use electricity as a means of generating sparks that could serve the same purpose in a laboratory.

Although the scientific work in this area was led by Sir Charles Wheatstone, who is best remembered for devising a device that bears his name (the Wheatstone Bridge) to enable accurate comparisons of electrical resistances, it was William Henry Fox Talbot who performed the experiment that is generally credited as having first married flash lighting and photography. Extensive research into this event has been undertaken by Pierre Bron and Philip Condax as part of their excellent book The Photographic Flash . Research led them to conclude that the oft-cited version of Fox Talbot’s experiment is unlikely to be completely accurate.

The usual version of the story, which records events that took place in 1851, has Fox Talbot photographing a front page of The Times newspaper that had been attached to a rapidly-rotating wheel. It moved with such speed that the newspaper was just a blur to the naked eye. The story also suggests that the spark that was used to illuminate the newspaper after the room had been darkened was provided by an electric charge that had been accumulated in Leyden jars. This last point is particularly appealing because Leyden jars were the first forms of capacitors. They provided a means of accumulating electrical charge over an extended period of time then releasing it in a split second, thus concentrating the electrical energy to produce a greater effect than would otherwise have been possible.

Unfortunately, Bron and Condax (drawing on letters exchanged between Fox Talbot and Michael Faraday) suggest that Leyden jars were not used, and that the electrical energy was drawn directly from a substantial battery. They also suggest that the amount of light generated would have been insufficient to illuminate an entire newspaper page, and propose instead that a small clipping could have been used. Fox Talbot’s letter to Faraday reports that in the photograph “the image of the printed letter was just as sharp as if the disc had been motionless,” which may mean that the printed paper, far from a newspaper, bore just a solitary character. Unfortunately the original glass plate has not survived so we may never know the truth.

James Killian, writing in the 1954 second edition of Harold Edgerton’s landmark book Flash!: Seeing the Unseen , attributes the birth of the stroboscope to the independent efforts of Joseph Plateau in Ghent and Simon Stampfer in Vienna, both of whom devised (non-photographic) devices in 1832 that gave the illusion of movement from a sequence of still images—a principle that also gave birth to the better known zoetrope. Although it seems that Plateau probably led the way (some sources date his invention a year earlier), it was Stampfer’s term “stroboscope” that triumphed over Plateau’s less elegant “phenakistoscope.”

The idea of using sparks to illuminate moving objects continued to fascinate scientists as photography developed, but the discoveries and techniques needed to manufacture an electronic flash tube simply did not exist. Xenon, which is the preferred gas for flash tubes because of its near-daylight effect on photographic film, was not extracted from the air by Georges Claude until the start of the 20th century. But other gases were used, especially at low pressure in discharge lighting, and Andre Crova appears to have used low gas pressures with spark electricity to create a stroboscope for freezing repetitive motion in 1873.

The first picture-based machine was Ottomar Anschutz’s electrotachyscope, which was unveiled in 1887. As its name suggests, this was a device that used electricity to examine how things changed with time: This idea was not dissimilar to Crova’s, but its application here was entirely photographic (Anschutz was a portrait photographer by profession). The machine employed a large hand-cranked wheel, around the perimeter of which was arranged a series of pictures taken using a bank of cameras in a manner similar to that employed ten years previously by Eadweard Muybridge to analyze a horse’s gallop under the patronage of Leland Stanford. When the wheel was rotated each picture in turn was placed in front of a flash tube that fired to project the image for viewing. The flash tube was connected to a different battery for each frame, thereby avoiding the need to accumulate more energy from the same source in a very short period of time, and the sequence of projected images gave the impression of realtime movement. Immediately hereafter the majority of allied photographic efforts were focused on capturing and replaying motion (leading to the development of motion picture film) and also on recording very high-speed events as part of scientific and engineering investigations.

High-Speed Developments

In 1917 Etienne Oehmichen, an engineer working for Peugeot who invented and built the first helicopters, developed an electrical stroboscope to examine engines while they were running. By 1935 he had succeeded in capturing pictures at a rate of 1100 frames per second, but it was the brothers Augustin and Laurent Seguin who provided the important breakthrough of accumulating electrical charge in capacitors to create sparks with more energy than could be provided instantaneously from a battery. In addition they realized that a second electrical source could be used to excite the gas in the flash tube, thereby making it conductive and able to convert the stored electrical energy into light. They also identified the fact that the triggering circuit could be activated by the mechanical movement of the object examined. Until this point workers had all used a single electrical circuit that both ionized the gas and caused it to emit light. Heavy-duty switches were needed to bring the substantial amount of electrical energy employed to bear on the gas-filled tube, making the necessary equipment bulky, hazardous, and unsuitable for connection to other machinery.

The Seguin brothers, who commenced manufacturing in 1926 after several years of practical research and development, realized that for the entire time the gas in a flash tube is non-conducting it can be connected directly to a source of electrical energy without diminishing it. As soon as the gas becomes conductive it can then draw on the already connected supply of electrical energy without any requirement for making and breaking a mechanical contact. They sold two electrical flash systems, Stroborama A and Stroborama B (both using neon tubes), to car and locomotive manufacturers who needed to study repetitive mechanical motion, and
by 1931 had achieved a flash duration of just 1/1,000,000 of a second. Impressive though this was, it would have been a fairly meaningless achievement if the moment of exposure had not been linked to an event that no human could possibly react to with equal speed to capture such pictures at the exact instant required. It is for this reason that the Seguin brothers, and not Etienne Oehmichen, are credited with having invented the electrical flash system as we know it.

Harold Edgerton

Three factors combined to make Harold Edgerton the most important figure in the history of modern electronic flash lighting. First, all the necessary foundations had already been laid and reliable flash lighting systems had proved their worth in science and industry as a means of capturing information that simply could not be seen with the naked eye. Secondly, by the 1930s books were starting to feature good quality photographic images (some even in color) without having to bear an uncomfortably high price penalty. Thirdly, photography as a whole was becoming more attractive to the general public thanks to improved emulsion sensitivities and the development of color films. Harold Edgerton’s expertise built on these foundations to create a flash system that had the same intensity as 40,000 standard 50W bulbs of the type that were common for domestic lighting in that time. Such was the brightness of this light that full surface detail and color could be seen in moving objects where previously little more than a silhouette had been recorded. A further strength of Edgerton’s work was the variety of different types of circuitry employed for triggering the flash exposure, including his use of microphones to initiate the picture-taking process.

This in turn highlights a difference in use between technical flash photography and flash pictures that were taken by the general public. Whereas the former could be undertaken in blacked-out rooms if necessary to record stroboscopic effects, the latter had to be compatible with everyday picture taking. Advances in chemical flash photography had already introduced automatic synchronization of the flashbulb with the lens aperture; the same had to be true for electronic flash if it were to be accepted for everyday use. The problem was that flashbulbs have a significant burn time (and also a significant delay before maximum brightness is achieved), whereas electronic flash is almost instantaneous in both respects. The result was a need for a new synchronization setting, which was marked X on camera bodies to distinguish it from the M that denoted flashbulb synchronization. Failure to use the correct setting in either case would result in a failed exposure.

Despite the change from single circuit to separately ionized flash tubes a remaining problem was the need for cameras to carry the full ionizing current through their synchronization contacts. Because of this cameras could be subjected to voltages in the range of 150 to 400V making electronic flash equipment potentially hazardous to use. This problem was solved first by using electronic valves and later by employing miniaturized semi-conductor circuitry, which dropped triggering voltages to as little as 5V in modern flash guns.

Modern Flash Units

The term “modern” applies here to any equipment that might reasonably be found in general use today. It therefore includes some items that may be considered old-fashioned together with others that are considered “cutting edge.”

The least portable modern flash systems are generator packs that are usually powered by a mains electricity supply but may feature integral rechargeable batteries for use on location. The packs contain substantial banks of capacitors and are fitted with control panels that allow users to vary their light output. Separate flash heads are attached to the pack by cables. An operational limitation is imposed by the maximum cable length that connects different heads to the same power pack. Triggering can be effected either via a cable that joins the camera to the power pack or using various types of wireless connection (short-range radio or infrared triggers). Maximum output is typically 3000J from one head and around 5000J from a single pack. Such units tend to be used only by professional photographers and as such a variety of different heads are offered to suit different demands. Generator flash systems, examples of which are made by the likes of Hensel, Balcar, Strobex, and especially the leading Swiss manufacturer Broncolor, are therefore similar to continuous light sources because their manufacturers respond to users’ needs by designing lights that are custom-made for specific applications.

An alternative, and more economical, approach to heavy-duty flash is provided by the monobloc design, which combines a control panel and flash head in a single unit that is plugged directly into the mains supply. In this case there is no cable between the power pack and the head because both components are contained within the same housing. Major manufacturers of these units include Elinchrom and Bowens: typical ratings are around 600J per unit but energies up to 1500Ws are common (there is no current agreement about whether flash heads should be rated in joules, which seem more elegant, or in watt-seconds). A variety of different light modifiers is provided by each manufacturer to adapt their standard flash heads for particular uses. Large softboxes, which provide almost shadowless illumination, are particularly popular.

Truly portable flash systems are always battery-based and are frequently mounted on the camera itself. Often there is no opportunity to modify the light output other than to focus it to match the angle of view of the lens fitted to the camera. Originally this operation was done manually but dedicated flash guns that exchange data with the camera to which they are connected can now do this automatically. There are still some battery-powered flash systems that have a power supply that is worn as a shoulder or belt pack, but most draw their energy from either rechargeable cells or disposable batteries that are housed within the flash gun itself. Among the sophisticated features that are offered by modern battery flash guns are stroboscopic flash, automatic exposure (see below), anti-redeye measures, balanced multiple-flash lighting, and modeling-lamp mode.

Exposure Control

The problem that affects flash photography the most is the difficulty of seeing and measuring the effect of the light. Experienced photographers can judge the effect of daylight and continuous artificial light by eye to make a good estimate of the exposure conditions needed to achieve a good image. The same thing is impossible with flash lighting, so manufacturers adopted the Guide Number System, wherein each flash head is given a number that can be used to determine the correct aperture to use for different flash-to-subject distances. The stated Guide Number is equal to the product of the lens aperture (f-stop) multiplied by the distance: Metric Guide Numbers are based on distances measured in meters for ISO 100 sensitivity. Thus a flash unit with a metric Guide Number of 40 requires a lens setting of f/8 when used at a distance of 5m to capture an image on ISO 100 film, and would require the lens aperture to be changed to f/10 if the distance were decreased to 4 m.

A subsequent development turned this idea on its head and allowed the photographer to choose a predetermined aperture. The flash gun then measured the amount of light reflected back from the subject and used a thyristor to either prolong or curtail its output (within limits) so that the best possible exposure could be obtained. This system worked well for common situations but was fooled by large objects either nearer or more distant than the main subject, as these things would significantly distort the flash gun’s interpretation of the amount of light that was reflected by the subject itself. When long-focus lenses were used this problem became particularly significant because there could be many objects closer to the camera that were excluded from the field of view, and to have an exposure based on these features would risk serious underexposure of the final image.

The solution was provided by Nikon, who introduced “distance technology” into its lenses. This allowed information about the range of the object on which the lens had focused to be passed to the flash gun via the camera so that an initial estimate of the correct aperture and flash power combination could be made prior to exposure. This is complemented by the amount of reflected light measured from the area of the film that coincides with the position of the autofocus sensor that was used to focus the lens. Additional measurements are taken from the rest of the image and all of these data are compared against patterns of brightnesses stored in the camera’s memory so that the very best exposure is recorded with minimal effort.

Digital cameras complicate this process because the reflection characteristics of their sensors do not match those of photographic film. For this reason automatic flash exposure quality suffered a setback during the early days of digital photography. Although this is no longer a serious problem, it does illustrate the difference in behavior between film and digital capture. This difference has also driven changes in lighting techniques and previously both threatened to make flash obsolete and, by the end of the 20th century, restored it as the dominant technology of choice for photographic use.

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about 2 years ago

please I'm a final year student and I'm doing my long modern lighting and I would like to ask a question.
Please, what is the impact modern lighting equipment has over photography?

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almost 3 years ago

Which was the first flash electronic commercial of the history? of Mecablitz? Leica? Nikon? Honeywel, other? and in what year it was thrown commercially? Which the first camera with built-in electronic flash?

Excuse my poor English. Mário Jorge Tavares - Londrina - Paraná - Brazil.

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almost 3 years ago

Which was the first flash electronic commercial of the history? of Mecablitz? Leica? Nikon? Honeywel, other? and in what year it was thrown commercially? Which the first camera with built-in electronic flash?

Excuse my poor English. Mário Jorge Tavares - Londrina - Paraná - Brazil.

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over 3 years ago

I enjoyed reading the article about the development of flash photography, and I learned a lot from it.
You might consider mentioning off-the-film (OTF) flash metering, which was a beneficial in using long lenses with flash, even without lens-to-flash communication. The Nikon system you describe must be a much later development.
Thanks again for the article.