The earliest flashes consisted of a quantity of magnesium flash powder that was ignited by hand. Later, magnesium filaments were contained in flash bulbs, and electrically ignited by a contact in the camera shutter; 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 coating flashbulbs with a plastic coating to improve spectral quality as well as providing protection from the rare occasion when a flashbulb would crack during a flash.
Flashbulbs took longer to achieve full brightness and burned for a longer duration than electronic flashes, and slower shutter speeds (typically from 1/10 to 1/50 of a second) were used on cameras to ensure proper synchronization. One of the most widely used flash bulbs up through the 1960s was the number 25.
This is the large (approximately 1 inch (25 mm) in diameter) flash bulb often shown used by newspapermen in period movies, usually attached to a press camera or a twin-lens reflex camera.
Flashcubes, Magicubes and Flipflash
In the late 1960s, Kodak improved their Instamatic camera line by replacing the individual flashbulb technology (used on early Instamatics) with the Flashcube.Flashcubes consisted of four electrically fired flashbulbs with an integral reflector in a cube-shaped arrangement that allowed taking four images in a row. The flashcube automatically rotated 90 degrees to a fresh bulb upon advancing the film to the next exposure.
The later Magicube retained the four-bulb format, and was superficially similar to the original Flashcube. However, in the Magicube each bulb was set off by a plastic pin in the cube mount that released a cocked spring wire within the cube. This wire, in turn, struck a primer tube, at the base of the bulb, which contained a fulminating material. The fulminate ignited shredded zirconium foil in the flash and, thus, a battery was not required. Magicubes could also be set off by inserting a thin object, such as a key or paper clip, into one of the slots in the bottom of the cube.
Another common flashbulb-based device was the Flipflash which included ten or so bulbs in a single unit. The name derived from the fact that once half the flashes had been used up, the unit had to be flipped and re-inserted to use the remainder.
Modern flash technology
As of 2003, the majority of cameras targeted for consumer use have an electronic flash unit built in. Another type of flash unit are microflashes, which are special, high-voltage flash units designed to discharge a flash of light with an exceptionally quick, sub-microsecond duration.
These are commonly used by scientists or engineers for examining extremely fast moving objects or reactions, famous for producing images of bullets tearing through objects like lightbulbs or balloons.
Studio flashes usually contain a modeling light, which is an incandescent light bulb placed close to the flash tube. The continuous illumination of a modeling light helps in visualizing the effect of the flash.
The strength of a flash device is often indicated in terms of a guide number , despite the fact that the published guide numbers of different units can not necessarily be directly compared.
Although they are not yet at the power levels to replace Xenon flash devices in still cameras, LEDs (specifically, high current flash LEDs from manufacturers like Lumileds or Seoul Semiconductor) have recently been used as flash sources in camera phones.
LEDs are expected to approach the power levels of Xenon in the near future and may replace built-in Xenon flashes in still cameras. The major advantages of LEDs over Xenon include low voltage operation, higher efficiency and extreme miniaturization.
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