i have a d90 and an sb-600. for some reason when i have the flash mounted on the hot shoe, it will flash a couple times and then take the shot. how do i get it to just take the shot? also, in commander mode, there is a delay from when i hit the shutter and when the shot actually goes off with the flash. i feel like an idiot here but i feel like ive tried all of the menu options. anyone have any ideas?