FujiFilm X-Pro1 Owner's Manual page 71

Flash Sync Speed Flash Sync Speed
The fl ash will synchronize with the shutter at shutter speeds of 1
The Sync Terminal The Sync Terminal
Use the sync terminal to connect fl ash units that require a sync cable.
Third-Party Flash Units Third-Party Flash Units
Do not use third-party fl ash units that apply over 300 V to the camera hot shoe.
/ 180 s or slower.
Flash Photography
55