I have used the 2 frame HDR feature in the D5100 and believe the D800 implementation will be the same. The camera takes two photos. While you only have to push the shutter release once, the shutter makes two distinct exposures. I use the HDR software built into CS5 but have never only used two exposures. Normally I use the bracket feature built into my camera and take 3 or 5 exposures.