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.
A 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.