Flash-lamp and flash powder lamp from 1909 Studies of
magnesium 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, a mixture of magnesium powder and
potassium chlorate, was introduced by its German inventors
Adolf Miethe 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 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.
Flashbulbs Wetzlar flash from 1950s The use of flash powder in an open lamp was replaced by
flashbulbs; magnesium filaments were contained in bulbs filled with
oxygen gas, and electrically ignited by a contact in the
camera 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. Subsequently, the magnesium was replaced by
zirconium, 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 to 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 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 or a
twin-lens reflex camera. 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 4 inches, initially developed for nighttime aerial photography during
World War II. 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 of a second—while most bulbs require a shutter speed of 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. File:AG-1 Flashbulb.jpg|The AG-1 flashbulb, introduced in 1958, used wires protruding from its base as electrical contacts; this eliminated the need for a separate metal base. File:Flashbulbs comparing AG-1 to No 75.jpg|Flashbulbs have ranged in size from the diminutive AG-1 to the massive No. 75. File:Brownie Hawkeye with Flash.jpg|
Kodak Brownie Hawkeye with "Kodalite Flasholder" and Sylvania P25 blue-dot daylight-type flashbulb File:Fototoestel met flits van het merk Philips - INDUS V09799.JPG|Bakelite camera with flash by the brand
Philips Flashcubes, Magicubes and Flipflash In 1965
Eastman Kodak of
Rochester, New York replaced the individual flashbulb technology used on early
Instamatic cameras with the
Flashcube developed by
Sylvania Electric Products. 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 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 was struck mechanically by a spring-loaded striker, which was cocked each time the film was advanced. Image:Magicube-Modified.jpg|Undersides of Flashcube (left) and Magicube (right) cartridges File:Flip Flash.jpg|"Flip flash" type cartridge
Electronic flash , firing The electronic flash tube was introduced by
Harold Eugene Edgerton 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, 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 circuitry to charge a high-capacitance
capacitor to several hundred
volts. When the flash is triggered by the shutter's flash synchronization contact, the capacitor is discharged rapidly through a permanent
flash tube, producing an immediate flash lasting typically less than of a second, shorter than shutter speeds used, with full brightness before the shutter has started to close, allowing easy
synchronization of maximum shutter opening with full flash brightness, unlike flashbulbs which were slower to reach full brightness and burned for a longer time, typically of a second. A single electronic flash unit is often mounted on a camera's
accessory shoe or a bracket; many inexpensive cameras have an electronic flash unit built in, with some cameras (such as the
Nikon Z50II) having both. For more sophisticated and longer-range lighting several synchronised flash units at different positions may be used.
Ring flashes that fit to a camera's lens can be used for shadow free portrait and 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
modelling light, a lamp close to the flash tube; the continuous illumination of the modelling light lets the photographer visualize the effect of the flash. LED lamps are replacing the previous
incandescent light bulbs in new designs, modelling lights typically being proportionately variable to flash power require dimmable LEDs and suitable circuitry in the head. Multiple flashes may be synchronised 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
monolights, is indicated in
watt-seconds.
Canon names its electronic flash units
Speedlite, and
Nikon uses
Speedlight; these terms are frequently used as generic terms for electronic flash units designed to be mounted on, and triggered by, a camera hot shoe.
High speed flash firing, taken with a high speed
air-gap flash. The photo was taken in a darkened room, with camera's shutter open and the flash was triggered by the sound of the shot using a microphone. An
air-gap flash is a high-voltage device that discharges a flash of light with an exceptionally short duration, often much less than one
microsecond. These are commonly used by scientists or engineers for examining extremely fast-moving objects or reactions, famous for producing images of
bullets tearing through light bulbs and balloons (see
Harold Eugene Edgerton). An example of a process by which to create a high speed flash is the
exploding wire method.
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 (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, , , 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: •
t0.1 is the length of time the light intensity is above 0.1 (10%) of the peak intensity •
t0.5 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 t0.5 value of and t0.1 of . 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, t0.5 and t0.1 decrease with decreasing intensity. Conversely, in cases where intensity is controlled by capacitor charge, t0.5 and t0.1 increase with decreasing intensity due to the non-linearity of the capacitor's discharge curve.
Flash LED used in phones integrated circuit High-current flash
LEDs 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, eliminating the need of a high-voltage capacitor. 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 (i.e., a
flashlight).
Focal-plane-shutter synchronization Electronic flash units have shutter speed limits with
focal-plane shutters. 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 s to 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 has a shutter travel time of about 2.4 ms. 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 2.4 ms + 1.0 ms = 3.4 ms, corresponding to a shutter speed of about s. However some time is required to trigger the flash. At the maximum (standard) D850 X-sync shutter speed of s, the exposure time is s = 4.0 ms, so about 4.0 ms − 2.4 ms = 1.6 ms are available to trigger and fire the flash, and with a 1 ms flash duration, 1.6 ms − 1.0 ms = 0.6 ms are available to trigger the flash in this Nikon D850 example. Mid- to high-end Nikon DSLRs with a maximum shutter speed of s (roughly
D7000 or
D800 and above) have an unusual menu-selectable feature which increases the maximum X-Sync speed to s = 3.1 ms with some electronic flashes. At s only 3.1 ms − 2.4 ms = 0.7 ms 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 s or s. Some cameras are limited to s. X-sync speeds for
medium format cameras when using focal-plane shutters are somewhat slower, e.g. 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 is 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 \sqrt{s/t} -->. 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 s (0.5 ms), the guide number reduces by a factor of \sqrt{0.5 / 5} -->, 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, the 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==