I've just read http://nodalninja.com/forum/index.php?topic=349.0
I am using this methode for a while.
On the NN site 53mm was standard, it is correct !
With the def. NN5, a 1/2mm is/can be added, so for a 5D it's 53,5 or 54mm.
Sure not 44 mm.
Mind you, I am using the supplied camera mount, the small block.
With this set up @44mm you will get a BIG SAW in Nadir........
@josejavier: do you use the camera mount/block ?
@Bill why did you change a lot of underrail values ??
Most (Canon) values did work rather well, not anymore.
And Hey, the NN3 and NN5 have different values, for sure, at least mine.
Have Fun !
The "a" distance in Camera Settings is for de canon 5d 53,5mm in my opinion this is wrong.My distance is 44,5.
I suggest you do a quick cross check using a different method. It takes only a minute or two to check the horizontal position by holding a plumb line in front of the lens to align the visible entrance pupil with the centre of the rotator knob. Level the head first, though. Details in http://www.johnhpanos.com/epcalib.htm.