ZR focus drive and capture controls

Part of the Nikon ZR reference. Read the overview for firmware, survey scope and evidence levels.

The ZR has no zoom or gimbal to drive. Its remote physical controls are the lens focus motor, the AF point, stabilization and the shutter. All of them share the single serial PTP command channel with the live-view fetch, so every drive below is bounded in wall-clock time.

AF area and tap to focus

ChangeAfArea (0x9205) moves the live-view AF point: p1 x, p2 y, in the live-view header’s whole-size coordinate space (6048×3400 on the ZR). Moving the point is not focusing. Whether a tap must also fire a one-shot AF drive depends on the mode:

Chrome	Focus mode	After the area move
Video	AF-C, AF-F	Nothing; the body’s continuous AF chases the new point
Video	AF-S	AfDrive (0x90C1) once, or the point moves and nothing focuses
Photo	Any AF mode	AfDrive once; stills live view does not run continuous AF until a half-press
Either	MF	Never drive; the body would refuse

An unknown mode keeps the earlier photo-only behavior. Each chrome reads and drives only its own focus mode: a stills-side focus event must not repaint the movie FOCUS readout or trigger an AF-S drive against a body in AF-C.

AF and MF drives

Operation	Parameters	Use
AfDrive 0x90C1	none	One-shot autofocus at the current point
AfDriveCancel 0x9206	none	Stop an in-flight drive and free the channel
MfDrive 0x9204	p1 1 toward near / 2 toward infinity, p2 pulses 1 to 32767	Focus-by-wire pull
DeviceReady 0x90C8	none	Readiness poll after a drive or release

MfDrive completion is read from the readiness poll. 0xA00C (step end) means the lens hit the end of travel; 0xA00E (step insufficiency) means the request was below what the lens can move. Device_Busy (a stepping-motor lens still initializing) and Access_Denied (AF still settling) are always transient.

Focus dial

The on-feed focus dial drives MfDrive in video and photo. Eligibility is one shared rule (PTPOperation.swift):

Body focus mode	Dial
Not read yet, or MF	Not offered; the lens ring owns focus
AF-F	Shown inert; full-time servo overrides every pull
AF-S, AF-C	Drivable; focus holds between acquisitions

The channel budget is wall clock, not a retry count: at most 12 readiness polls at 0.12 s inside one drive, and at most 1.2 s of refusal retries at 0.08 s. An AF tap pre-empts an in-flight drive rather than queueing behind it.

Observed (field report on a Z 6III, #272): when a drive overran the readiness poll on a native Z-mount STM lens, the body answered busy to ChangeAfArea until a half-press. The app now sends AfDriveCancel when the poll ceiling is reached, so tap-to-focus is not wedged. The still release that follows a dial pull uses the no-AF form so the pull is kept (see still release).

Tracking release

A focus reset that must recenter while subject tracking is engaged runs a release sequence before ChangeAfArea:

1. EndTracking (0x9425, [ZR-only · verify-on-HW]), then AfDriveCancel.
2. Temporarily set subject detection to Off and the AF area from Subject tracking to Single, only where they were active.
3. Wait for the live-view header to show the tracking lock cleared, within a frame budget.
4. ChangeAfArea to the center.
5. Repeat EndTracking and AfDriveCancel. Observed: ChangeAfArea can re-latch target tracking on ZR hardware.
6. Restore the saved AF area and subject detection unless the operator changed them during the reset. Restoration writes mode settings only; it never starts tracking.

The decision reads the live-view header as well as the polled properties, because polled values can lag while tracking is already engaged.

ChangeAELock (0x9426) is cataloged but not used by either app.

Stabilization

Property	Values	Evidence
MovieVibrationReduction 0xD1F9	0 OFF, 1 ON, 2 SPORT	Code in libgphoto2; value table [ZR-only · verify-on-HW]
ElectronicVR 0xD314	0 Off, 1 On	[verify-on-HW]
ElectronicFrontCurtainShutter 0xD20D	Off / On	Stills only; not polled

The command monitor summarizes the first two as one stabilization readout. Stabilization behavior also varies with lens, recording mode and firmware.

Still release

InitiateCaptureRecInMedia (0x9207) is preferred wherever advertised, with InitiateCapture (0x100E) as the fallback. Its first parameter selects the release:

p1	Release
0xFFFFFFFE	AF drive, then release: a half-press then fire, like the body’s shutter button
0xFFFFFFFF	Plain release with no AF step; keeps a focus-dial pull

[verify-on-HW]: that 0xFFFFFFFF skips AF while the body is in an AF focus mode.

In the continuous release modes a remote release latches until TerminateCapture (0x920C), so the shutter control ends the burst on finger up ([verify-on-HW] per body). The stills shutter property 0xD100 also carries the open-shutter sentinels 0xFFFFFFFF Bulb, 0xFFFFFFFD Time and 0xFFFFFFFE X-sync. Busy answers during a release include 0xA200 (bulb release busy), 0xA201 (silent release busy) and 0xA202 (movie frame release busy); DeviceReady is classified while a release is in flight.

Shots released on the body itself register in the app from the event poll (ObjectAdded, CaptureComplete), not from the PTP-IP event socket. The interval and focus-shift operations 0x9445 to 0x9447 exist on generation 3 bodies and remain [verify-on-HW].