JTL S-25M Master AC Slave Strobe, Guide Number 72, ISO 100, Feet Output: 25 watt seconds Guide Number: 72 Size & Weight: 3" in diameter x 5 1/2" long / 6 ounces Triggering: Slave, PC Synch Cord or Test Button Flash Duration: 1/1000 - 1/500 of a second