There are problems with optical slaves however. If you are using several flashes in a brightly lit area, the slaves may not ‘see’ the master flash fire due to the brightness level and then will not trigger the other units.  There is no cure here unless you can turn off the lights to make the room brightness lower, then when the flash fires, the optical slaves pick up the brightness change easier and will trigger their respective flashes.The content you are trying to access is only available to members. Sorry.