Okay folks, here's my situation... I have D90, SB-600 speedlight and an Opus Pro OPL H250 mono light. If I have the sb-600 off camera, fired wirelessly with the D90 in commander mode and the sb in TTL it will not fire the mono light (optical slave) If I put the sb on the camera it will fire the mono light. If I use the pop-up flash on the camera it will fire the mono light. If I take the Sb off camera and set it to wireless / manual mode it will still not fire the mono light. It seems that when the camera is in commander mode it will not fire the mono light, but it will fire the sb-600. Why would the SB-600 not then fire the mono light? What am I doing wrong here? If I am looking for a 2 light setup it seems now that I must either have 2 mono lights in manual mode or 2 speedlights in Nikon's CLS system. Can I not combine the two systems?