So, for those who are interested in what's happening with my case of dealing with D800 focus problem - I've got my camera back from it's second trip to Nikon's service center.
I was told that everything operates within specifications in terms of focus performance. I don't know what or how they were testing my camera and if they even bothered to test it during the second service round - few dust particles that were in the mirror chamber after the first trip to the same facility are still there. So I'm not sure if anyone was doing anything serious in the camera.
I spend some time running tests again. Different target this time - star chart. Two lenses - my original 50mm and 70-200mm to make sure that no-one can just brush me off saying "maybe your lens is at fault".
As I said before - after first trip my left sensor got much better at the expense (?) of the center sensor. As a matter of fact I do not see how center sensor can be usable at all at this point with large apertures. My last round of tests is clearly showing that the focus performance is the same for different lenses.
Any idea of "color temperature" and other factors affecting focusing at this point just make no sense - if left and right sensors manage to focus to a decent degree, but center sensor fails - then there is hardly any "color temperature" problem here.
Also I doubt that AF fine tune would do anything here - as I understand, fine tuning is not done on a per sensor base, it's a global adjustment for a particular lens. So while it's possible to get center sensor to operate better I would believe that other sensors would suffer from this adjustment.
I put up complete test result on my blog since I have tools there to make the issue clearly visible and comparable. If you are interested - please take a look at the post here:
And for those who don't want to visit some other site - here are only 2 images - Live View and Phase Detect from center sensor which clearly show the issue:
So, with all this in mind I have few possible scenarios:
1. Nikon does not have proper procedure to fix the issue 2. There are different kinds of problems with focus mechanism and only some cases can be fixed/adjusted while other - cannot 3. Only few Nikon service centers are capable of fixing this 4. Nikon doesn't really care about this issue and tries to brush off as many customers as possible and doing something to those few who are either too well known or raise too many problems.