Hi guys recently my nikon SB 600 feels like its underpowered. Usually, when i am shooting from a distance of about 5m, using bounce flash, the picture looks well exposed, but recently when using the same technique, distance and also the ceiling height, the picture looks dark, sometimes the flash did not even appear in the picture(the pic looks like flash had not been used), which puzzles me. I pumped the flash power to the max, it still remain underpowered. Even when i use direct flash, it looks dark. i wonder if there is something wrong with the bulb, or the camera(i doubt so). Anyone care to share what's wrong?