Lens serial communication

[coderat]

[lain]

To clarify: the pulses are sent whether you use AF or manually turn the focus ring, but they are only sent when the lens is set to M/A mode. In M mode, manually turning the focus ring does not send pulses, and of course it cannot AF.

[astronomer]

[lain]

[coderat]

Ok, what is clear from Nikon repair manual: there is GMR head and GMR encoder. They check GMR head readed signal on GMR board directly with Oscilloscope by turning MF ring manually and A/M switch position doesn't matter here.

On another side GMR encoder is tested with a connector to lens F-Mount, setting "focus mode selection" to A, supplying 6VDC for lens AF motor driving with moving focus by motor.

Why lens do not encode GMR signal in M mode is strange for me...

Best regards,
coderat

[lain]

[coderat]

[lain]

So I just slapped the test rig on my D800, still with the AF-S DX 35mm f/1.8G lens, and indeed pin 8 is being driven.
Pin 8 is definitely 90deg out of phase to pin 5, and the direction of phase shift determines direction of the AF motor.
Same as before with pin 5 (and pin 8) "going dark" in M mode, and coming alive only in M/A mode.

Here's how they look on the 'scope:

.. and the logic analyzer:

So I guess the lower-end cameras only get the amount, but the higher-end cams also get feedback on direction.
This signal is almost certainly generated by the lens, though I wonder why it wouldn't emit the signal anyway on the D5100 if that's the case? Maybe because the D800 sends 02 1B in response to command 0x40, whereas the D5100 sends 02 1A...
Hmmm

[lain]

By the way, if it's useful to anybody, here's the D5100's behavior when no lens is attached:

As you would expect, it just pulls H/S low then releases it, waiting for a lens to hold it low in response so the camera can send a command.

[coderat]