So today I went to a special event going on at my local Hunt's Photo and Video and I was part of the audience in a couple seminars. Something I learned today was how to use my SB-600 Flash unit wirelessly while still being able to use the onboard flash on my camera. I had an idea that this was possible, or at least I assumed, but I never knew how, until today. So as a way to help others with my experiences, here's today's tip. Keep in mind that this technology works via infrared and not radio waves, like the pocket wizard receivers, so in order for this to work the camera has to have a line of site to the flash unit. So this is a cheap way to use a second or third flash unit on the cheap.
Turn flash unit on and reset by holding down the (zoom) and (-) buttons down together for a couple seconds and the flash unit will reset. Once this is done, the HUD on the flash should have a wave with an arrow and say OFF.
Push (+) until it says ON.
In the camera menu go to the CUSTOM SETTINGS MENU, and go to the Bracketing/Flash option, then go to "Flash control for built-in flash."
Go down to Commander mode and select whether our not you want to use TTL(Through The Lens), Manual, or none for flash control. At the bottom there should be an option to change the CHANNEL. By default the channel on the flash will go to channel 3 zone A. (That can be change on the flash by pressing mode and pressing (+) or (-). Select a channel on both the flash and camera that should be the same.
When I did this it did not work. The reasons for this is because the flash unit was not in the Line-of-sight of the camera, and also because in the camera menu my channel was not the same. Once I fixed this it still did not work. I then changed the built in flash option to TTL with no exposure compensation and also changed the GROUP B option to TTL as well with 0 exposure compensation. All of these options in the camera allow you to change the exposure compensation up to 3 Stops above or below where you are at. This helps to be more creative and manage the power output of the flash units in the built in and the separate unit.
Keep in mind that I was using a Nikon D90 with the built-in flash and a Nikon SB-600 flash unit. I hope this works for you, and if it does feel free to comment. Any questions or comments leave them below. Thanks.