I have a mix of standard studio slave flashes and Canon Speedlites (430 EX IIs and 600EX RT) – this allows great flexibility for outdoor and indoor work (studio) however it was challenging to get this equipment to work well together. The problem is that the non Canon equipment would not sync with the Canon Slaves and would flash too soon.
There are many solutions to this problem – all of which require buying more equipment (for example I could switch to Canons new radio equipment) but I choose the following solution because it is 100% reliable without additional cost by just configuring the equipment I already owned to work together.
Here is how I did it:
Firstly, a cheap Studio Slave (the most common) will never utilize Canons ETTL-H high speed flash sync – so all of the flashes have to be set to manual mode and the Canon Camera has to have its shutter speed set at the flash sync speed, typically 1/200 for Canon (or less).
Canon speedlites don’t easily facilitate syncing with non Canon flash since Canon utilizes an instructional pre-flash emitted by the Master Speedlite intended to establish the flash settings for other Canon Slaves (Canons version of a Slave using what Canon refers to as Optical Sync), however this instructional pre-flash will trigger the Studio Strobes into firing early. This is because most studio strobes are set to slave mode by using an optical sensor to fire when they see a flash (typically from the master flash).
Solution: My Menik studio strobe has an option to flash on the second or third trigger flash which is the key to synchronization between Canon and non Canon equipment. By pushing the Cell button on the Menik slave till indicator 2 is lit (meaning red eye in Menik talk) the Menik will flash with on the second flash it sees (the first being the Canon instructional pre-flash). This will cause the Menik Studio Slave to fire along with the other Canon slaves.
Another zero cost option is to use just one Canon flash mounted on the camera hot shoe in Flash Manual Mode as the Master along with the Studio Slave. There will be no pre-flash as there are no Canon slaves. Aiming the camera mounted flash in Flash Manual Mode at the ceiling may provide acceptable results with the studio flash a the key flash (or visa versa as desired). Use of a flash extension cord may be helpful as well.
My thanks to Syl Arena http://pixsylated.com/blog/ for defining the problem and clues on how I could address this.