Based upon extensive experience/testing I would say the Nikon AF system is actually quite simple and logical/progressive, even though it's not really well explained.
Irregardless of the iteration of the AF system the basics are the same.
You start with single point. Then you add additional points around it to aid in acquiring/maintaining AF (group mode if avail, 25pts in the D5/D500). Then you add even more additional points for tracking/maintaining focus w/ erratic subjects (dynamic modes).
Group mode functions in a nearest priority.
Dynamic modes use 9pts for initially acquiring/maintaining AF, and also function in something of a nearest priority for both acquiring and maintaining focus (the 9pt and group areas were the same size/area in previous models).
3D is the same as full dynamic mode (d153), but adds in color information and scene recognition from matrix metering.
Auto evaluates all focus points for best focus, it also uses scene recognition w/ matrix metering, and it also functions in a nearest priority mode.
In all cases only one point is used for focus, although several points may report as having been w/in focus tolerance.
The main difference between the D5/D500 and earlier models is that the dynamic modes used to function in something of a nearest priority and would not refocus unless focus was lost. The D5/D500 dynamic modes do not function in a nearest priority and will refocus even if focus is not lost. This is a VERY significant difference... and no-one is sure if it is intentional or not as it's not been officially addressed/acknowledged.
Mar 28, 2017 at 10:51 AM
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