Just took a nadir shot to look at centre alignment and whilst the white line on the clamp is perfect, the centre mark on my Kirk bracket doesn't run true to the centre screw on the rotator ( I'm sure I read someone else noticed this issue). I'm assuming the tripod screw on the D800 is to the centre of the camera, if anyone knows otherwise I would appreciate it. Anyway I offset the mark a couple of mm and now it runs straight down the line over the centre rotating screw on the tripod. In other words when I take a nadir shot and open it in Photoshop the 2 guide lines meet in the middle of the screw on top of the rotator. Have I done right? Also fine-tuned my settings :
D800 with Kirk 'L' bracket centred using the right placed mark on the bracket
14-24mm @14mm URS 155mm, LRS 135.5mm
Hope this helps someone.