My new D800 has Left/Right AF issues too :(

Hi TOF,

Here is a curve like the one given by focal. It is an AFS 24-70mm at 24mm and f2.8. The blue and the red dots are shots done at a given AF Fine Tune value.

First thing you will notice is that with the same AFFT value and different attempts, you'll get different sharpness. It is due to the fact that an AF system never focuses exactly at the same point. Forget about the green curve which is an interpolation to find the best AF Fine Tune. I prefer to do that manually and my guess is that -3 is the best AF Fine Tune value here.

On a range from -8 to +3 (which is a span of 11 AF Fine Tune units), the sharpness is quite good. The target is just moving inside the depth of field. I am not sure you'll find that much difference looking at the sharpness of the target.

Therefore, I would say that the width of the depth of field (looked at 100% with a D800) is about 10 AF Fine Tune units.

One think it would be smaller at f1.4, but Nikon plays the following tricks: the AF Fine Tune scale is done so that the width of the depth of field is always about 10 units in the AF Fine Tune scale for a lens when it is wide open. Therefore, however fast is your lens, the "width" of this curve will be about the same. You can do the following experiment: take a f1.4 (or f1.8) lens and Fine Tune it. Then add 10 units to your best AF Fine Tune and take a picture focusing on a target close to a "slanted ruler" or whatever proxy you want. Then do the same with an f4 lens. You'll find out that the depth of field has moved way more with the f4 lens.

By the way, would you mind sharing your Reikan plot ?