#1. "RE: SU-4" In response to Reply # 0 Fri 07-Sep-12 02:22 PM by Luke_Miller
Rural Virginia, US
I use the SU-4 fairly regularly in an all manual flash setup in my small basement studio. I put one of my old (pre-iTTL) flashes on it for use as a background or hair light.
Recently I started using it on location to light the background when using my SB-800 on camera. The SU-4 flash is set to manual, while the on-camera flash is in TTL mode. The TTL pre-flash will trigger the SU-4 flash creating the possibility that the SU-4 unit won't recycle quick enough to trigger from the main flash.
To prevent this I use the FV Lock function. FV Lock generates the pre-flash and calculates the flash exposure, but does not fire the main flash. The SU-4 fires on this pre-flash, but FV Lock then eliminates pre-flashes in the subsequent exposures. So I have effectively created a manual flash configuration using TTL. After FV Lock is set, the SU-4 flash fires only from the SB-800's main flash.
If you check your SB-700 manual, you will see the SB-700 has a built-in SU-4 mode, pages D-3 and D-18. The SB-800/900/910 also have a built-in SU-4 mode.
The SU-4 is a hang over accessory from the TTL film cameras and Speedlights. The SU-4 base has an optical sensor, as does your SB-700, that will trigger a flash unit attached to the SU-4's hot shoe. The attached light will either flash (M - Manual mode) or stay on as long ss the master flash is firing (A-Auto mode). Since the SU-4 uses an optical sensor, the sensor must be along the unobstructed line of sight to the master flash. This also applies to the built-in sensor on the Speedlight.
When using the SU-4 or the SU-4 mode the remote flash unit is in the manual flash mode and you will need to set the level of light emitted from the remote on the remote unit. This is the power level.
You should have received the SU-4 Instruction Manual when you purchased the SU-4. There are pictures there that can help.
You can also use the Advance Wireless features of your cameras and the SB-700 to automatically compute the exposure for all the Nikon CLS flash units you are using.