The Strobies Pro-Flash One Eighty can be used either on or off camera when used OFF camera the system really comes in to its own when used with the dedicated Radio Trigger Set STR203 which runs on 2 x standard AA batteries all of its functions can then be controlled at up to 50m away using any of the 16 channels from the camera position. The Proflash has five useable flash modes including Manual S1 S1 Slave Triggering Mode function as a slave flash for creating multiple lighting effects. S2 Slave Triggering RPT Strobo Flash. S2 Slave Triggering In this mode the flash units function as a slave flash for creating multiple lighting effect & will ignore a single preflashfrom the master flash firing only on the second flash from any other flash unit. The PRO-Flash One Eighty is powered by an external 11. 1V4500m Ah Lithium-Ion Battery pack providing 900 flashes at full-power recycling in 2. 2 seconds. Unlike regular speedlight shoe-mount camera flashguns it is best used off camera when using the light-shaping tools. The 360 spread from the bare bulb flash tube allows for an even distribution of light from softboxes & beauty dishes.