The STR203 Strobies Radio Transmitter Set RTS can only be used with the PRO flash range of products its primary use is to control all functions of the PROflash at up to 50 metres away within any of its 16 Channels. In addition it also enables the high speed sync function where by the user can now use Shutter Speeds above the camera maximum setting for flash typically up to 18000th of a second. By adding this combination to the STR200 kit you open up a whole new world of flash photography for Sport & Wildlife or any other social event.