One thought. On the SB-800 display the flash shows an underexposure value after the exposure if the flash could not put out the requested amount of light. When I mistakenly had my lens set at f/22 my flash with 0 compensation showed a -2/3 EV under exposure. The other flash that was set at -1.3 compensation did not display any underexposure value. Make sure your flash shows that it was able to provide the requested power.
Gary in SE Michigan, USA. Co-organizer of the Southern Michigan Chapter Nikonians membership - My most important photographic investment, after the camera. D4, D810, D300, D90, F6, FM3a (black), FM2n (chrome) YashicaMat 124, Graflex Speed Graphic 4x5 My Nikonians Gallery & Our Chapter Gallery