Flash (photography)
A flash is a device used in photography that produces a brief burst of light at a color temperature of about 5500 K to help illuminate a scene. The main 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 cameras 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. In professional studio equipment, flashes may be large, standalone units, or studio strobes, powered by special battery packs or connected to mains power. They are either synchronized with the camera using a flash synchronization 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 and flash powder
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 harmless bit of pyrotechnics.
Flashbulbs
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 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 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 had a faster ignition time, 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.
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 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.
Electronic flash
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 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.