I should know this...

[David_Buzzard]

I've been using the SU-800 flash controller with both the SB-900 and SB-800 flashes. I like it, but I can only the two flashes fire at the same time I put one in the 'A' group, and one in the 'B' group. If I leave them both in the same group and use different channels, only one will fire. There must be a way of getting all the channels in a group to fire, but I'm just missing it. I'd like to add some more flashes

[Luke_Miller]

As I understand it the channel asignment should be the same for all flashes you want to control. The four channel choices allow other CLS users to pick different chanels so as not to interfere. Each group can have multiple flashes in it. All flashes in a group use the same settings (Mode, Exposure Compensation). The SU-800 supports three Groups unless you are in Close-up mode - then it is two groups. All groups fire simultaneously (as long as they are set to the same channel). I typically put my main light in Group A, Fill Light in B and background light in C. I can then set each light's output individually. If I didn't need to set them to different settings I could put all of them in Group A.

[DierkHaasis]

The channel setting determines the communication canal between the sender and the receiver[s]. Any flash you want to fire needs to be on the same channel as the commander unit. Only the group setting puts flashes apart.

[David_Buzzard]

There's actually a little switch in the battery compartment that changes the mode from macro photography to flash controller. Once I figured that out, it works much better.

David Buzzard