I recently purchased a Nikon F100 and Nikon N80 with Nikon 800 Speedlight. I have tamron lens 28-300 with Macro capability. I also have the Flash on a bracket. I've been assisting a professional wedding photographer and using her N80 and Medium format Fuji for the season. She has been very happy with my work. Now, when I use the F100 with Speedlight 800 that I purchased at the weddings most of my work is seriously underexposed. I fill a bit lost with the higher power flash? I don't really know if I should be using the diffuser or not either. I do lots of weddings in Churches, some outside work, and at reception halls. I am really an ameteur and have alot to learn. I have a Wedding to do on my own in April and I'll be using my equipment. The photographer I work with is very impressed with my work, but now with my own equipment I seem to be a mess. I do most of my work on Automatic/Program mode and TTL or TTL BL flash. Like I said, I'm just learning. Any help out there, tips, advice? Thanks.