You know that on many cameras, like the Canon 7D or the Nikon D90, you can use your camera’s pop-up flash to drive other flashes. Or you can use an on-camera “master/commander” flash to do the same:
A student asked me yesterday: “how do I turn the on-camera flash off, so it does not flash, and only the external flash fires?”
I told her how to set the on-camera flash to off. On Nikons, in the flash section of the pencil menu you set it to “-”; on Canons you select the option where only the external flash shows, so only it will fire.
“But it is still firing”, she mailed me back.
No. It is not. That is a misconception. Try this: turn off the external flash, then shoot. You see the flash, but the picture is all dark!
How come? What were you seeing?
You were just seeing the flash fire commands at any external flashes in the room, using “morse code”. I.e. you were seeing TTL preflash activity, not a “real” flash, fired when the shutter is open. This was just techie stuff, all before the mirror is raised and the shutter opens. After the shutter is open, nothing.
It helps to know these little techie facts, doesn’t it?
For more: http://photonetworkexpo.com/ : come see me talk this weekend in Toronto about Flash Photography, and even better: book online and use promo code Michael2013 to get 50% off a weekend pass. See you then!