Yesterday I did Auto AF fine tune for the two main lenses .. 24-70mm and 70-200 +/- TC 14E III on Nikon D850.
It took me a good 2 hours
I had to buy a collar for the 70-200 f4 to put on tripod safely ..
I did each lens, at each focal end, 10 times. I then averaged the value for the lens .. while keeping the values for each end saved on my mobile, in case I want to use at one end or the other exclusively in a critical shoot .. I had to do the 70-200 with and without the extender ..
The reason for doing 10 times each one is that the process is so critical .. even pressing the button on the camera makes a very fine vibration, that affects the value significantly .. I think Nikon have to change the process, so it is hands free, using a shutter release cable or timer instead.
At the end of the day .. the 24-70mm was spot on .. calibration value is zero .. i.e. doesn’t need any
The 70-200mm value is +5 without and +7 with Teleconverter
Wow .. that was a whole evening ..
It is easier than AF fine tune manually .. because I am depending on the camera to give a value, rather than trying to decide myself, based on a chart photo, which value to go for .. It is not as easy as they meant it to appear. There is some software out there that can do that, but still requires a lot of trials. I used a Datacolor Spyder LensCal as my target, only because I owned it already.
Averaging across focal end lengths and doing it at certain distances, showed the value different for different focal lengths and distances .. I therefore did it for longest Focal Length first, wide open and nearest subject first .. because that’s the shallowest DOF, as my main value, then for the shorter focal length .. Anything placed further or using the wider focal length, and the DOF would give enough tolerance for good focus, without the need of fine adjustments, as long as the lens is not an outlier of course. I averaged the values, with more weight towards the longest focal length value.
It is easier to do on prime lenses.