Canon E-TTL Metering and Optical Studio Slaves

Hi.all.

If you are using studio lights that are triggered by optical slave units,
does this
mean that the flashes will be triggered too soon by Canon's E-TTL Metering?

The reason I ask is because with the E-TTL metering, the camera sends out
two flashes, one for the metering, and a second one straight afterwards for
the actual photo. Does this mean that the first 'metering flash' will
trigger the flash units? If so, is there a way round it as I can't find a
way to turn it off?

 

Don't use a Canon flash at all - just connect the studio flash(s) using the
flash socket on the camera, or by a hotshoe adaptor.

 

1) Can you set you flash to manual so it only sends out the exposure
flash? (What I do (Minolta system) is put on an accessory flash and
set it to Manual at 1/16 or 1/32 power. In this mode only one sync'd
flash goes out).

2) You can get slave devices from Wein that will 'skip' the first flash
and trigger the lights on the second flash pulse. Just plug this slave
in the PC sync socket of the strobe and disable the strobes own slave
sensor.

3) Connect a PC sync cabel to the camera's PC sync or hotshoe (may need
an adaptor) and fire the flash that way.

Cheers,
Alan