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A flash is a device used in
photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...
that produces a brief burst of light (typically lasting 1/1000 to 1/200 of a second) at a
color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
of about 5500  K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light. ''Flash'' refers either to the flash of light itself or to the electronic flash unit discharging the light. Most current flash units are electronic, having evolved from single-use flashbulbs and flammable powders. Modern
camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...
s often activate flash units automatically. Flash units are commonly built directly into a camera. Some cameras allow separate flash units to be mounted via a standardized accessory mount bracket (a ''
hot shoe Canon EOS 350D Hot shoe Proprietary hot shoe used by Minolta and older Sony cameras (Konica Minolta Maxxum 7D">Sony.html" ;"title="Minolta and older Sony">Minolta and older Sony cameras (Konica Minolta Maxxum 7D) A hot shoe is a mounting poin ...
''). In professional studio equipment, flashes may be large, standalone units, or studio strobes, powered by special battery packs or connected to
mains power Mains electricity or utility power, power grid, domestic power, and wall power, or in some parts of Canada as hydro, is a general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to h ...
. They are either synchronized with the camera using a
flash synchronization In photography, flash synchronization or flash sync is the synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor. In cameras with mechanical (clockwor ...
cable or radio signal, or are light-triggered, meaning that only one flash unit needs to be synchronized with the camera, and in turn triggers the other units, called ''slaves''.


Types


Flash-lamp/Flash powder

Studies of
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
by Bunsen and Roscoe in 1859 showed that burning this metal produced a light with similar qualities to daylight. The potential application to photography inspired Edward Sonstadt to investigate methods of manufacturing magnesium so that it would burn reliably for this use. He applied for patents in 1862 and by 1864 had started the Manchester Magnesium Company with Edward Mellor. With the help of engineer William Mather, who was also a director of the company, they produced flat magnesium ribbon, which was said to burn more consistently and completely so giving better illumination than round wire. It also had the benefit of being a simpler and cheaper process than making round wire. Mather was also credited with the invention of a holder for the ribbon, which formed a lamp to burn it in. A variety of magnesium ribbon holders were produced by other manufacturers, such as the Pistol Flashmeter, which incorporated an inscribed ruler that allowed the photographer to use the correct length of ribbon for the exposure they needed. The packaging also implies that the magnesium ribbon was not necessarily broken off before being ignited. An alternative to magnesium ribbon was
flash powder Flash powder is a pyrotechnic composition, a mixture of oxidizer and metallic fuel, which burns quickly and produces a loud noise regardless of confinement. It is widely used in theatrical pyrotechnics and fireworks (namely salutes, e.g., cherry ...
, a mixture of magnesium powder and
potassium chlorate Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. After sodium chlorate, it is the second most common chlorate in industrial use. ...
, was introduced by its German inventors
Adolf Miethe Adolf Miethe (; 25 April 1862, Potsdam – 5 May 1927, Berlin) was a German scientist, lens designer, photochemist, photographer, author and educator. He co-invented the first practical photographic flash and made important contributions to the p ...
and Johannes Gaedicke in 1887. A measured amount was put into a pan or trough and ignited by hand, producing a brief brilliant flash of light, along with the smoke and noise that might be expected from such an explosive event. This could be a life-threatening activity, especially if the flash powder was damp. An electrically triggered flash lamp was invented by Joshua Lionel Cowen in 1899. His patent describes a device for igniting photographers’ flash powder by using dry cell batteries to heat a wire fuse. Variations and alternatives were touted from time to time and a few found a measure of success, especially for amateur use. In 1905, one French photographer was using intense non-explosive flashes produced by a special mechanized
carbon arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s ...
to photograph subjects in his studio, but more portable and less expensive devices prevailed. On through the 1920s, flash photography normally meant a professional photographer sprinkling powder into the trough of a T-shaped flash lamp, holding it aloft, then triggering a brief and (usually) harmless bit of
pyrotechnics Pyrotechnics is the science and craft of creating such things as fireworks, safety matches, oxygen candles, explosive bolts and other fasteners, parts of automotive airbags, as well as gas-pressure blasting in mining, quarrying, and demolition ...
.


Flashbulbs

The use of flash powder in an open lamp was replaced by ''flashbulbs''; magnesium filaments were contained in bulbs filled with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
gas, and electrically ignited by a contact in the
camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...
shutter. Manufactured flashbulbs were first produced commercially in Germany in 1929. Such a bulb could only be used once, and was too hot to handle immediately after use, but the confinement of what would otherwise have amounted to a small explosion was an important advance. A later innovation was the coating of flashbulbs with a plastic film to maintain bulb integrity in the event of the glass shattering during the flash. A blue plastic film was introduced as an option to match the spectral quality of the flash to daylight-balanced
colour film Color photography is photography that uses media capable of capturing and reproducing colors. By contrast, black-and-white or gray- monochrome photography records only a single channel of luminance (brightness) and uses media capable only of ...
. Subsequently, the magnesium was replaced by
zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
, which produced a brighter flash. There was a significant delay after ignition for a flashbulb to reach full brightness, and the bulb burned for a relatively long time, compared to shutter speeds required to stop motion and not display camera shake. Slower shutter speeds (typically from 1/10 to 1/50 of a second) were initially used on cameras to ensure proper synchronization and to make use of all the bulb's light output. Cameras with
flash sync In photography, flash synchronization or flash sync is the synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor. In cameras with mechanical (clockwor ...
triggered the flashbulb a fraction of a second before opening the shutter to allow it to reach full brightness, allowing faster shutter speeds. A flashbulb widely used during the 1960s was the Press 25, the flashbulb often used by newspapermen in period movies, usually attached to a
press camera A press camera is a medium or large format view camera that was predominantly used by press photographers in the early to mid-20th century. It was largely replaced for press photography by 35mm film cameras in the 1960s, and subsequently, by ...
or a
twin-lens reflex camera A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" (the lens that takes the picture), while the other is used for the viewfind ...
. Its peak light output was around a million lumens. Other flashbulbs in common use were the M-series, M-2, M-3 etc., which had a small ("miniature") metal bayonet base fused to the glass bulb. The largest flashbulb ever produced was the GE Mazda No. 75, being over eight inches long with a girth of 14 inches, initially developed for nighttime aerial photography during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. The all-glass PF1 bulb was introduced in 1954. Eliminating the metal base and the multiple manufacturing steps needed to attach it to the glass bulb cut the cost substantially compared to the larger M series bulbs. The design required a fibre ring around the base to hold the contact wires against the side of the glass base. An adapter was available allowing the bulb to fit into flash guns made for bayonet-capped bulbs. The PF1 (along with the M2) had a faster ignition time (less delay between shutter contact and peak output), so it could be used with X synch below 1/30 of a second—while most bulbs require a shutter speed of 1/15 on X synch to keep the shutter open long enough for the bulb to ignite and burn. A smaller version which was not as bright but did not require the fibre ring, the AG-1, was introduced in 1958; it was cheaper, and rapidly supplanted the PF1.


Flashcubes, Magicubes and Flipflash

In 1965
Eastman Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...
of
Rochester, New York Rochester () is a City (New York), city in the U.S. state of New York (state), New York, the county seat, seat of Monroe County, New York, Monroe County, and the fourth-most populous in the state after New York City, Buffalo, New York, Buffalo, ...
replaced the individual flashbulb technology used on early
Instamatic : ''For the film formats associated with the ''Instamatic'' and ''Pocket Instamatic'' camera ranges, see 126 film and 110 film respectively.'' The Instamatic is a series of inexpensive, easy-to-load 126 and 110 cameras made by Kodak beginning ...
cameras with the ''Flashcube'' developed by
Sylvania Electric Products Sylvania Electric Products Inc. was an American manufacturer of diverse electrical equipment, including at various times radio transceivers, vacuum tubes, semiconductors, and mainframe computers such as MOBIDIC. They were one of the companies inv ...
. A flashcube was a module with four expendable flashbulbs, each mounted at 90° from the others in its own reflector. For use it was mounted atop the camera with an electrical connection to the shutter release and a battery inside the camera. After each flash exposure, the film advance mechanism also rotated the flashcube 90° to a fresh bulb. This arrangement allowed the user to take four images in rapid succession before inserting a new flashcube. The later Magicube (or X-Cube) by General Electric retained the four-bulb format, but did not require electrical power. It was not interchangeable with the original Flashcube. Each bulb in a Magicube was set off by releasing one of four cocked wire springs within the cube. The spring struck a primer tube at the base of the bulb, which contained a fulminate, which in turn ignited shredded
zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
foil in the flash. A Magicube could also be fired using a key or paper clip to trip the spring manually. ''X-cube'' was an alternate name for Magicubes, indicating the appearance of the camera's socket. Other common flashbulb-based devices were the Flashbar and Flipflash, which provided ten flashes from a single unit. The bulbs in a Flipflash were set in a vertical array, putting a distance between the bulb and the lens, eliminating red eye. The Flipflash name derived from the fact that once half the flashbulbs had been used, the unit had to be flipped over and re-inserted to use the remaining bulbs. In many Flipflash cameras, the bulbs were ignited by electrical currents produced when a
piezoelectric crystal Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''p ...
was struck mechanically by a spring-loaded striker, which was cocked each time the film was advanced.


Electronic flash

The electronic flash tube was introduced by
Harold Eugene Edgerton Harold Eugene "Doc" Edgerton (April 6, 1903 – January 4, 1990), also known as Papa Flash, was an American scientist and researcher, a professor of electrical engineering at the Massachusetts Institute of Technology. He is largely credited with ...
in 1931. The electronic flash reaches full brightness almost instantaneously, and is of very short duration. Edgerton took advantage of the short duration to make several iconic photographs, such as one of a bullet bursting through an apple. The large photographic company Kodak was initially reluctant to take up the idea. Electronic flash, often called "strobe" in the US following Edgerton's use of the technique for
stroboscopy A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces b ...
, came into some use in the late 1950s, although flashbulbs remained dominant in amateur photography until the mid 1970s. Early units were expensive, and often large and heavy; the power unit was separate from the flash head and was powered by a large lead-acid battery carried with a shoulder strap. Towards the end of the 1960s electronic flashguns of similar size to conventional bulb guns became available; the price, although it had dropped, was still high. The electronic flash system eventually superseded bulb guns as prices came down. Already in the early 1970s, amateur electronic flashes were available for less than $100. A typical electronic flash unit has
electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electric ...
ry to charge a high-capacitance
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
to several hundred
volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...
s. When the flash is triggered by the shutter's flash synchronization contact, the capacitor is discharged rapidly through a permanent
flash tube Flash, flashes, or FLASH may refer to: Arts, entertainment, and media Fictional aliases * Flash (DC Comics character), several DC Comics superheroes with super speed: ** Flash (Barry Allen) ** Flash (Jay Garrick) ** Wally West, the first Kid ...
, producing an immediate flash lasting typically less than 1/1000 of a second, shorter than shutter speeds used, with full brightness before the shutter has started to close, allowing easy
synchronization Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
of maximum shutter opening with full flash brightness, unlike flashbulbs which were slower to reach full brightness and burned for a longer time, typically 1/30 of a second. A single electronic flash unit is often mounted on a camera's
accessory shoe Canon EOS 350D Hot shoe Proprietary hot shoe used by Minolta and older Sony cameras (Konica Minolta Maxxum 7D">Sony.html" ;"title="Minolta and older Sony">Minolta and older Sony cameras (Konica Minolta Maxxum 7D) A hot shoe is a mounting poin ...
or a bracket; many inexpensive
camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...
s have an electronic flash unit built in. For more sophisticated and longer-range lighting several synchronised flash units at different positions may be used.
Ring flash A ring flash is a circular light that is often operated with a camera lens in the center to take photographs. Unlike point light sources, a ring flash can illuminate a subject with minimal shadows by closely and evenly surrounding the optical ax ...
es that fit to a camera's lens can be used for shadow free macro photography; some lenses have built-in ring-flash. In a photographic studio, more powerful and flexible studio flash systems are used. They usually contain a
modeling light A flash is a device used in photography that produces a brief burst of light (typically lasting 1/1000 to 1/200 of a second) at a color temperature of about 5500  K to help illuminate a scene. A major purpose of a flash is to illuminate a ...
, an
incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxi ...
close to the flash tube; the continuous illumination of the modeling light lets the photographer visualize the effect of the flash. A system may comprise multiple synchronised flashes for multi-source lighting. The strength of a flash device is often indicated in terms of a guide number designed to simplify exposure setting. The energy released by larger studio flash units, such as
monolight A monolight is a self-contained photographic flash lighting unit usually found in a studio. Each monolight has its own independent power source. It does not depend on a centralized power supply as a "pack and head" system does. Monolights are als ...
s, is indicated in
watt-seconds The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...
.
Canon Canon or Canons may refer to: Arts and entertainment * Canon (fiction), the conceptual material accepted as official in a fictional universe by its fan base * Literary canon, an accepted body of works considered as high culture ** Western ca ...
names its electronic flash units Speedlite, and
Nikon (, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group. Nikon's products include cameras, camera ...
uses Speedlight; these terms are frequently used as generic terms for electronic flash equipment.


High speed flash

An
air-gap flash An air-gap flash is a photographic light source capable of producing sub-microsecond light flashes, allowing for (ultra) high-speed photography. This is achieved by a high-voltage (20 kV typically) electric discharge between two electrodes o ...
is a high-voltage device that discharges a flash of light with an exceptionally short duration, often much less than one
microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 ...
. These are commonly used by scientists or engineers for examining extremely fast-moving objects or reactions, famous for producing images of
bullet A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. Bullets are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax. Bullets are made in various shapes and co ...
s tearing through light bulbs and balloons (see
Harold Eugene Edgerton Harold Eugene "Doc" Edgerton (April 6, 1903 – January 4, 1990), also known as Papa Flash, was an American scientist and researcher, a professor of electrical engineering at the Massachusetts Institute of Technology. He is largely credited with ...
). An example of a process by which to create a high speed flash is the
exploding wire method The exploding wire method or EWM is a way to generate plasma that consists in sending a strong enough pulse of electric current through a thin wire of some electrically conductive material. The resistive heating vaporizes the wire, and an electric ...
.


Multi-flash

A camera that implements multiple flashes can be used to find depth edges or create stylized images. Such a camera has been developed by researchers at the
Mitsubishi Electric Research Laboratories Mitsubishi Electric Research Laboratories (MERL) is a subsidiary of Mitsubishi Electric US Holdings, Inc., which, in its turn, is the principal subsidiary of Mitsubishi Electric in the United States. MERL is the North American arm of the Corpora ...
(MERL). Successive flashing of strategically placed flash mechanisms results in shadows along the depths of the scene. This information can be manipulated to suppress or enhance details or capture the intricate geometric features of a scene (even those hidden from the eye), to create a non-photorealistic image form. Such images could be useful in technical or medical imaging.


Flash intensity

Unlike flashbulbs, the intensity of an electronic flash can be adjusted on some units. To do this, smaller flash units typically vary the capacitor discharge time, whereas larger (e.g., higher power, studio) units typically vary the capacitor charge. Color temperature can change as a result of varying the capacitor charge, making color correction necessary. Constant-color-temperature flash can be achieved by using appropriate circuitry. Flash intensity is typically measured in stops or in fractions (1, 1/2, 1/4, 1/8 etc.). Some monolights display an "EV Number", so that a photographer can know the difference in brightness between different flash units with different watt-second ratings. EV10.0 is defined as 6400 watt-seconds, and EV9.0 is one stop lower, i.e. 3200 watt-seconds.


Flash duration

Flash duration is commonly described by two numbers that are expressed in fractions of a second: * t.1 is the length of time the light intensity is above 0.1 (10%) of the peak intensity * t.5 is the length of time the light intensity is above 0.5 (50%) of the peak intensity For example, a single flash event might have a t.5 value of 1/1200 and t.1 of 1/450. These values determine the ability of a flash to "freeze" moving subjects in applications such as sports photography. In cases where intensity is controlled by capacitor discharge time, t.5 and t.1 decrease with decreasing intensity. Conversely, in cases where intensity is controlled by capacitor charge, t.5 and t.1 increase with decreasing intensity due to the non-linearity of the capacitor's discharge curve.


Flash LED used in phones

High-current flash
LEDs A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...
are used as flash sources in camera phones, although they are less bright than xenon flash tubes. Unlike xenon tubes, LEDs require only a low voltage. They are more energy-efficient, and very small. The LED flash can also be used for illumination of video recordings or as an autofocus assist lamp in low-light photography; it can also be used as a general-purpose non-photographic light source.


Focal-plane-shutter synchronization

Electronic flash units have shutter speed limits with
focal-plane shutter In camera design, a focal-plane shutter (FPS) is a type of photographic shutter that is positioned immediately in front of the focal plane of the camera, that is, right in front of the photographic film or image sensor. Two-curtain shutters ...
s. Focal-plane shutters expose using two curtains that cross the sensor. The first one opens and the second curtain follows it after a delay equal to the nominal shutter speed. A typical modern focal-plane shutter on a full-frame or smaller sensor camera takes about 1/400 s to 1/300 s to cross the sensor, so at exposure times shorter than this only part of the sensor is uncovered at any one time. The time available to fire a single flash which uniformly illuminates the image recorded on the sensor is the exposure time minus the shutter travel time. Equivalently, the minimum possible exposure time is the shutter travel time plus the flash duration (plus any delays in triggering the flash). For example, a
Nikon D850 The Nikon D850 is a professional-grade full-frame digital single-lens reflex camera (DSLR) produced by Nikon. The camera was officially announced on July 25, 2017 (the 100th anniversary of Nikon's founding), launched on August 24, 2017, and firs ...
has a shutter travel time of about 2.4ms. A full-power flash from a modern built-in or hot shoe mounted electronic flash has a typical duration of about 1ms, or a little less, so the minimum possible exposure time for even exposure across the sensor with a full-power flash is about 2.4ms + 1.0 ms = 3.4ms, corresponding to a shutter speed of about 1/290 s. However some time is required to trigger the flash. At the maximum (standard) D850 X-sync shutter speed of 1/250 s, the exposure time is 1/250 s = 4.0ms, so about 4.0ms - 2.4ms = 1.6ms are available to trigger and fire the flash, and with a 1ms flash duration, 1.6ms - 1.0ms = 0.6ms are available to trigger the flash in this Nikon D850 example. Mid- to high-end Nikon DSLRs with a maximum shutter speed of 1/8000 s (roughly
D7000 The Nikon D7000 is a 16.2-megapixel digital single-lens reflex camera (DSLR) model announced by Nikon on September 15, 2010. It replaced the D90 as the top end consumer camera, by using much of the technology and controls from the earlier D5000, ...
or D800 and above) have an unusual menu-selectable feature which increases the maximum X-Sync speed to 1/320 s = 3.1ms with some electronic flashes. At 1/320 s only 3.1ms - 2.4ms = 0.7ms are available to trigger and fire the flash while achieving a uniform flash exposure, so the maximum flash duration, and therefore maximum flash output, must be, and is, reduced. Contemporary (2018) focal-plane shutter cameras with full-frame or smaller sensors typically have maximum normal X-sync speeds of 1/200 s or 1/250 s. Some cameras are limited to 1/160 s. X-sync speeds for
medium format Medium format has traditionally referred to a film format in photography and the related cameras and equipment that use film. Nowadays, the term applies to film and digital cameras that record images on media larger than the used in 35&n ...
cameras when using focal-plane shutters are somewhat slower, e.g. 1/125 s, because of the greater shutter travel time required for a wider, heavier, shutter that travels farther across a larger sensor. In the past, slow-burning single-use flash bulbs allowed the use of focal-plane shutters at maximum speed because they produced continuous light for the time taken for the exposing slit to cross the film gate. If these are found they cannot be used on modern cameras because the bulb must be fired *before* the first shutter curtain begins to move (M-sync); the X-sync used for electronic flash normally fires only when the first shutter curtain reaches the end of its travel. High-end flash units address this problem by offering a mode, typically called FP sync or HSS ( High Speed Sync), which fires the flash tube multiple times during the time the slit traverses the sensor. Such units require communication with the camera and are thus dedicated to a particular camera make. The multiple flashes result in a significant decrease in guide number, since each is only a part of the total flash power, but it's all that illuminates any particular part of the sensor. In general, if s is the shutter speed, and t is the shutter traverse time, the guide number reduces by . For example, if the guide number is 100, and the shutter traverse time is 5 ms (a shutter speed of 1/200s), and the shutter speed is set to 1/2000 s (0.5 ms), the guide number reduces by a factor of , or about 3.16, so the resultant guide number at this speed would be about 32. Current (2010) flash units frequently have much lower guide numbers in HSS mode than in normal modes, even at speeds below the shutter traverse time. For example, th
Mecablitz 58 AF-1 digital
flash unit has a guide number of 58 in normal operation, but only 20 in HSS mode, even at low speeds.


Technique

As well as dedicated studio use, flash may be used as the main light source where ambient light is inadequate, or as a supplementary source in more complex lighting situations. Basic flash lighting produces a hard, frontal light unless modified in some way. Several techniques are used to soften light from the flash or provide other effects.
Softbox A soft box is a type of photographic lighting device, one of a number of photographic soft light devices. All the various soft light types create even and diffused lightBrooks, David. ''How to Control and Use Photographic Lighting''. HPBooks, ...
es, diffusers that cover the flash lamp, scatter direct light and reduce its harshness. Reflectors, including
umbrellas An umbrella or parasol is a folding canopy supported by wooden or metal ribs that is usually mounted on a wooden, metal, or plastic pole. It is designed to protect a person against rain or sunlight. The term ''umbrella'' is traditionally used ...
, flat-white backgrounds, drapes and reflector cards are commonly used for this purpose (even with small hand-held flash units). Bounce flash is a related technique in which flash is directed onto a reflective surface, for example a white ceiling or a flash umbrella, which then reflects light onto the subject. It can be used as fill-flash or, if used indoors, as ambient lighting for the whole scene. Bouncing creates softer, less artificial-looking illumination than direct flash, often reducing overall contrast and expanding shadow and highlight detail, and typically requires more flash power than direct lighting. Part of the bounced light can be also aimed directly on the subject by "bounce cards" attached to the flash unit which increase the efficiency of the flash and illuminate shadows cast by light coming from the ceiling. It's also possible to use one's own palm for that purpose, resulting in warmer tones on the picture, as well as eliminating the need to carry additional accessories.
Fill flash Fill flash is a photographic technique used to brighten deep shadow areas, typically outdoors on sunny days, though the technique is useful any time the background is significantly brighter than the subject of the photograph, particularly in back ...
or "fill-in flash" describes flash used to supplement ambient light in order to illuminate a subject close to the camera that would otherwise be in shade relative to the rest of the scene. The flash unit is set to expose the subject correctly at a given aperture, while shutter speed is calculated to correctly expose for the background or ambient light at that aperture setting. Secondary or slave flash units may be synchronized to the master unit to provide light from additional directions. The slave units are electrically triggered by the light from the master flash. Many small flashes and studio monolights have optical slaves built in. Wireless radio transmitters, such as
PocketWizard The PocketWizard is a wireless radio triggering system for off-camera lighting developed in the late 1990s, by LPA Design, an American company based in South Burlington, Vermont. It requires a transmitter electrically connected to the camera, usu ...
s, allow the receiver unit to be around a corner, or at a distance too far to trigger using an optical sync. To strobe, some high end units can be set to flash a specified number of times at a specified frequency. This allows action to be frozen multiple times in a single exposure. Colored gels can also be used to change the color of the flash. Correction
gels A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...
are commonly used, so that the light of the flash is the same as tungsten lights (using a CTO gel) or fluorescent lights. Open flash, Free flash or manually-triggered flash refers to modes in which the photographer manually triggers the flash unit to fire independently of the shutter.


Drawbacks

Using on-camera flash will give a very harsh light, which results in a loss of shadows in the image, because the only lightsource is in practically the same place as the camera. Balancing the flash power and ambient lighting or using off-camera flash can help overcome these issues. Using an umbrella or softbox (the flash will have to be off-camera for this) makes softer shadows. A typical problem with cameras using built-in flash units is the low intensity of the flash; the level of light produced will often not suffice for good pictures at distances of over or so. Dark, murky pictures with excessive
image noise Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the image sensor and circuitry of a scanner or digital camera. Image noise can also originate in ...
or "grain" will result. In order to get good flash pictures with simple cameras, it is important not to exceed the recommended distance for flash pictures. Larger flashes, especially studio units and monoblocks, have sufficient power for larger distances, even through an umbrella, and can even be used against sunlight at short distances. Cameras which automatically flash in low light conditions often do not take into account the distance to the subject, causing them to fire even when the subject is several tens of metres away and unaffected by the flash. In crowds at sports matches, concerts and so on, the stands or the auditorium can be a constant sea of flashes, resulting in distraction to the performers or players and providing absolutely no benefit to the photographers. The "
red-eye effect The red-eye effect in photography is the common appearance of red pupils in color photographs of the eyes of humans and several other animals. It occurs when using a photographic flash that is very close to the camera lens (as with most compact ...
" is another problem with on camera and ring flash units. Since the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
of the
human eye The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. ...
reflects red light straight back in the direction it came from, pictures taken from straight in front of a face often exhibit this effect. It can be somewhat reduced by using the "red eye reduction" found on many cameras (a pre-flash that makes the subject's
iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...
es contract). However, very good results can be obtained only with a flash unit that is separated from the camera, sufficiently far from the
optical axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light pro ...
, or by using bounce flash, where the flash head is angled to bounce light off a wall, ceiling or reflector. On some cameras the flash exposure measuring logic fires a pre-flash very quickly before the real flash. In some camera/people combinations this will lead to shut eyes in every picture taken. The blink response time seems to be around 1/10 of a second. If the exposure flash is fired at approximately this interval after the TTL measuring flash, people will be squinting or have their eyes shut. One solution may be the FEL (flash exposure lock) offered on some more expensive cameras, which allows the photographer to fire the measuring flash at some earlier time, long (many seconds) before taking the real picture. Unfortunately many camera manufacturers do not make the TTL pre-flash interval configurable. Flash distracts people, limiting the number of pictures that can be taken without irritating them. Photographing with flash may not be permitted in some museums even after purchasing a permit for taking pictures. Flash equipment may take some time to set up, and like any grip equipment, may need to be carefully secured, especially if hanging overhead, so it does not fall on anyone. A small breeze can easily topple a flash with an umbrella on a lightstand if it is not tied down or sandbagged. Larger equipment (e.g., monoblocks) will need a supply of AC power.


Gallery

File:AG-1 flash.tif , Front and back views of an Agfa ''Tully'' flash attachment for AG-1 flashbulbs, 1960 File:Metz 171 mecablitz.jpg, Metz 171 mecablitz - Compact electronic flash. Made in Germany, Metz-Werke GmbH & Co. KG, 1967 File:Metz 171 mecablitz disassembled.jpg, Metz 171 mecablitz - compact electronic flash disassembled File:Bauer E 251.jpg, Bauer E 251 - Compact automatic flash with built-in rechargeable battery Made in Germany, Robert Bosch Photokino GMBH, 1969 File:Bauer E 251 Disassembled.jpg, Bauer E 251 electronic flash disassembled File:Minolta electronic flashlamp ca 1978.tif, Front and back views of a Minolta ''Auto 28'' electronic flashlamp ca 1978


See also

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Battery–capacitor flash A battery–capacitor flash (BC flash) is a flash photography system used with flashbulbs. Instead of relying directly on the current pulse ability of a photoflash battery to directly fire a flashbulb, a battery is used to charge a capacitor ...
*
List of photographic equipment makers This list of photographic equipment makers lists companies that manufacture (or license manufacture from other companies) equipment for photography. Camera and lens manufacturers Note that producers whose only presence in the photo industry a ...
*
Flash comparison A list of flash guns, for easy comparison of strobes, from different manufactures. The list is intended to supplement the list of photographic equipment makers. List of current models List of discontinued models {, class="wikitable" border ...
*
Flashtube A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
*
Through-the-lens metering In photography, through-the-lens metering (TTL metering) refers to a feature of cameras whereby the intensity of light reflected from the scene is measured through the lens; as opposed to using a separate metering window or external hand-held lig ...


References


Further reading

* * * * * *


External links


"Flash Photography with Canon EOS Cameras – Part I"
PhotoNotes.org. 12 December 2010.
"A Minolta/Sony Alpha Flash Compendium"
Fotografie. *  . Gordon McKinney.

David L. Brittain.

. Bart Zieba Photography. {{Authority control Photographic lighting Light sources Articles containing video clips