Hot shoe
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A hot shoe is a mounting point on the top of a camera to attach a flash unit. The hot shoe is shaped somewhat like an inverted, squared-off 'U' of metal. The matching adapter on the bottom of the flash unit slides in from the back of the camera and is secured by a clamping screw on the flash. In the center of the 'U' is a metal contact point. This is used for standard, brand-independent flash synchronization. Normally the metal of the shoe and the metal of the contact are electrically isolated from each other. To fire the flash, these two pieces are shorted together. The flash unit sets up a circuit between shoe and contact - when it is completed by the camera, the flash fires.
In addition to the central contact point, many cameras have additional metal contacts within the 'U' of the hot shoe. These are proprietary connectors that allow for more communication between the camera and a 'dedicated flash'. A dedicated flash can communicate information about its power rating to the camera, set camera settings automatically, transmit color temperature data about the emitted light, and can be commanded to light a focus-assist light or fire a lower-powered preflash for focus-assist, metering assist or red-eye effect reduction.
