Content included: PT-04CN Wireless Flash Trigger set with 2 receivers. (flash holder, ballhead and screw adapter not included and sold separately.) The PT-04 wireless flash trigger is a low-cost while reliable radio remote flash triggering system. It can trigger hot shoe flashgun from your digital camera wirelesslly. The system contains 2 parts called transmitter and receiver. The power consumption of the system is very low and with 2 brand new Alkaline batteries the receiver can work over hundreds of times and the transmitter standby time can be over 1 year. The receiver takes 2 x AAA batteries (not included) and due to the design of the systme it can only use Alkaline batteries. Max sync speed of the system is 1/250th second. Channels: 4 Control Channels . Frequency: 433MHZ . Working Range: Up to 20 meters (open area without interference). Shutter Sync Speed: Up to 1/250th second . Transmitter Battery: 23A 12V small battery (included) . Receiver Battery: 2 x AAA batteries (not included) . Operating temperature: 5 °C to 40 °C (40 °F to 105 °F) . Trigger current: 0.01mA. Transmitter standby time: > 1 year (with a new battery) . Compatible with following flash units: Canon: 580EX II, 580EX, 550EX, 540EZ, 520EZ, 430EX, 430EX II, 430EZ, 420EX, 420EZ, 380EX... Nikon: SB-900, SB-700, SB-800, SB-80Dx, SB-600, SB-28, SB-27, SB-26, SB-25, SB-24 . Pentax: AF-540 FGZ, AF-360 FGZ, AF-400 FT, AF-240 FT ...Olympus: FL-50, FL-40, FL-36 ...Vivitar: 285HV (Older Vivitar 285/283 works only with PC sync) . Please make sure you turn off your flash unit before it's mounted onto the trigger set. The trigger set isn't compatible with some Nissin flash units (except Nissin Nikon fit with firmware upgraded).