Novatron Vari-power 400 W/S Power Pack (Digital Camera Ready) Power (Watt Seconds): Variable, 400 Ws maximum Guide Number: Typical Guide Number Std. Head @ 10'/ISO 100: 208 @ full power Typical f/Stop Std. Head @ 10'/ISO 100: f/5.6 @Minimum - Greater Than f/16.5 @Full power Recycling Time: 2.5 secs @ full power Power Range: seamless variable power over a three stop range (down to 1/8 power) Power Distribution: Symmetrical