Thanks for the responses. I'll be diving in Indonesia and want enough with my 8mm 1.8 lens to cover animals like manta rays, sharks, etc... Also, I want enough coverage for extensive clear water reef scenes. I already have a YS-D2 but I think it will be easier having two of the same strobe. Yes, the backscatter strobes are heavy and powerful. Wouldn't I want all the juice I can get, and just use the YS-D2 for macro? Also, do you find a significant improvement using RC over TTL? Thanks again for all the help. When I'm not diving the tropics I will be in the cold waters of the Pacific Northwest, where maybe I don't need as much power because of the subject matter.