Some observation of patents/manuals and investigation different lens types result in following information:
|Pin||AF||AF-S 8-pin||AF-S 10-pin||Description|
|1||x||x||x||Vcc Power for Lens chip (5V)|
|2||x||x||x||Serial read/write selection|
|3||x||x||x||Serial clock output|
|4||x||x||x||Serial data input/output|
|5||x||x||Pulse train. Number of pulses corresponds to amount of focus change, frequency of pulses corresponds to rate of focus change. Generated when lens is in M/A mode when focus changes by AF or manual focusing. Unused when lens is in M mode.|
Open-collector output, must be pulled high in the camera body in order to function.
Output on this line is controlled by bit 1 of command 0xEA.
|6||x||x||Vmotor Power for Zoom, VR, Autofocus (high current).|
This pin seems to be a regulated line around 6.2V (Tested on D800 with and without battery grip, D5100, and F5).
|8||x||x||Pulse train (same as pin 5) but 90° out of phase. The direction of phase shift to pin 5 tells direction of movement. This pin is not connected on consumer DSLR bodys (tested D5100) and no signal was measured. Connected on Pro-bodies.|
Like pin 5, this is an open-collector output and must be pulled high in the camera body.
Output on this line is controlled by bit 0 of command 0xEA.
Each type of lens connector support all pins from previous version and introduce new extension pins for a new functionality. The evolution of F-mount connector: AF -> AF-S 8-pin -> AF-S 10-pin. Old AF lens can still have autofocus using mechanical coupling that is available in some high-end cams like D7000.
The most interesting rumor is that Nikon Pro Bodys have better Autofocus. There are several facts that approve this:
- Nikon Pro Bodys use batteries with higher voltage. For example, D3 uses EN-EL4a rated 11.1V or D4 EN-EL18 rated 10.8V, against D5100 with EN-EL14 rated 7.4V.
It seems this higher battery voltage is not made available to lenses. Additionally, testing many lenses at different voltages (separately from camera bodies) shows consistent AF speed regardless of Vbat. Nevertheless, the possibility of a lens negotiating access to higher voltage has not been ruled out.
- Nikon Pro Bodys have AF-S 8-pin connector for lens interface against AF-S 7-pin on consumer bodys. Example: D3 against D5100. We now know Pin 8 of AF-S interface comes from the lens focus sensor and provides information on the direction of focus change, in addition to the amount and rate of focus change provided by Pin 5 to all bodies. Note, that JPEG EXIF value of focus distance on consumer body is inaccurate and seems to come with serial data.
Each lens identifies with its own LensID Extensive list can be found at Robert Rottmerhusen LensID pages
Electrical interface: Lens Serial Interface