Wein Digital Smart Slave (SSLD) - Smart Slaves are designed to ignore preflash used with many digital cameras. This is NOT for use with red-eye reduction features, only with digital preflash. It allows you to place a flash at a better angle for more professional flash shots with a digital camera. The preflash on digital cameras is used to set the color balance. A normal Slave unit would fire with the preflash in error.