Slave flash

A slave flash is an external flash unit that provides extra lighting when it is triggered by a built-in camera flash, or any other flash for that matter.

Slave flash setupA slave unit is particularly useful for those who want a more powerful flash but don’t have a hot shoe on their digital camera. An external flash that has a wireless transmitter lets it also function as a slave flash.

A slave flash has a built-in sensor that senses when the camera flash goes off. When the flash goes off, it triggers the slave flash, often within milliseconds.

A slave flash often comes with a bracket that has a hot shoe at one end. The bracket is screwed into the tripod mount on the bottom of a camera, then the flash is mounted on the bracket hot shoe. The flash requires no cable.

Slave flash features may include:

  • selectable power levels
  • zoom capability
  • vertical bounce angle
  • 360 degree swivel

Slave flash and digital camera compatibility

A slave unit must be compatible with a digital camera.

Slave flashes typically fire on a first flash. Since many digital cameras emit a series of pre-flashes before the main flash goes off, the pre-flashes can trigger a slave unit prematurely for it to be useful.

Manufactures make slave units specifically designed for digital cameras, which fire on the second flash. Some also have a learning mode that profiles a camera. The learning mode teaches the slave unit the number of pre-flashes for a given digital camera.

Limitation of a slave flash

A limitation of a slave flash is that it can be triggered by the flash by another camera that’s in use in the same room.

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