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A ring flash, invented by Lester A. Dine in 1952, originally for use in dental photography, is a circular photographic flash that fits around the lens, especially for use in macro (or close-up) photography. Its most important characteristic is providing even illumination with few shadows visible in the photograph, as the origin of the light is very close to (and surrounds) the optical axis of the lens. When the subject is very close to the camera, as is the case in macro photography, the distance of the flash from the optical axis becomes significant. For objects close to the camera, the size of the ring flash is significant and so the light encounters the subject from many angles in the same way that it does with a conventional flash with soft box. This has the effect of further softening any shadows.
Ring flashes are also very popular in portrait and fashion photography. In addition to softening shadows and creating circular highlights in the model's eyes, the unique way that a ring flash renders light gives the model a shadowy halo that is a common feature of fashion photography.
A macro ring flash usually consists of two parts:
- a power and control unit mounted on a hot shoe, and
- a circular flash unit mounted on the front of a lens.
Power is supplied by batteries in the shoe-mount unit, and a cord relays the power and control signals to the circular flash unit.
For larger ring flash units like those used for fashion photography, power is usually delivered by a power pack which can be battery or AC powered. Some ring flashes, however, like ones made by Paul C. Buff, Inc. under the "AlienBees" trademark, are constructed like mono lights where the light and power are contained in one unit.
Within the circular flash unit, there can be one or more flash tubes, each of which can be turned on or off individually. Some ring flashes have focusing lamps for helping low-light focusing. Also available are ring flash diffusers, which have no light source of their own, but instead mount in front of a conventional flash unit and transmit the light to a ring-shaped diffuser at the front of the lens.
There are also passive light modifiers, which will shape the light from an ordinary (shoe mount) flash into that of a ring flash. The adapters use a series of diffusers and reflectors to "bend" the light in an arc around the lens axis. The light is then emitted from that arc. This maintains any through-the-lens (TTL) lighting functions that may be shared by the camera and flash, as the actual light source has not changed.
Ring flash as a lighting technique has enjoyed a strong resurgence over the last few years,[when?] as photographers realize that it is far more useful than the one-look way in which it has been used for decades. Specifically, it is now being used primarily as a fill light to raise the illumination level of shadows created by other, off-axis lights. It is considered[by whom?] to be a particularly good source of fill light, because it does not create harsh shadows.
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