In certain TTL situations, especially when shooting in full sun or over long distances, the normal pre-flash is simply not enough for the camera to see. Now, when Pre-Flash Boost is engaged, you get a pre-flash that is two stops brighter. This will approximately double the distance that the camera can make sense of the pre-flash E-TTL information or help compensate for the reduced output caused by a diffuser over the flash or a bounced flash.
Pre-Flash Boost can be engaged for your on-camera flash by simply angling the flash head in any direction other than the standard 90º position. Pre-Flash Boost is engaged on a remote FlexTT5 by default, regardless of flash head position.
The PocketWizard Utility allows you to set Pre-Flash Boost modes independently for a local/on-camera flash or a remote flash. This is done on the Flash Tab.
- “Local Preflash Boost Mode” is for a flash mounted on the MiniTT1 or FlexTT5 when it is used as a transmitter on the camera.
- “Remote Preflash Boost Mode” is for a flash mounted on the FlexTT5 when used as a remote receiver.Setting this mode on a FlexTT5 used as a transmitter will not engage Pre-Flash Boost for other FlexTT5 radios used as remote receivers. It must be set on each remote FlexTT5 individually.
- “Force Preflash Boost” turns Pre-Flash Boosts on full-time (helpful when using diffusers). This is the default setting for a remote FlexTT5.
- “Auto Preflash Boost” enables Pre-Flash Boost whenever the flash head is rotated in any direction other than the standard 90º position. In the standard 90º flash head position, Pre-Flash Boost will not be used. This is the default setting for a MiniTT1 or FlexTT5 used as a transmitter.
- “Disable Preflash Boost” turns Pre-Flash Boost off.
Pre-Flash Boost is compatible with the following Speedlites only:
580EX, 580EX II, 430EX, 430EX II, 270EX
Pre-Flash Boost is not compatible with the following Speedlites and will be automatically disabled: 220EX, 550EX, 420EX
It is also not compatible with the Metz 58 AF-1 or 48 AF-1 Canon. When using these flashes you must manually set both Pre-Flash Boost modes to “Disable Preflash Boost” in the Utility.