Auto Capture

A kingfisher has a favourite dead branch over a pond. Suppose it lands there four times in a five-hour afternoon and stays twenty seconds each time. That is 80 seconds of bird in 18,000 seconds of waiting, or $80 / 18{,}000 \approx 0.44\%$ of the afternoon. The figures are illustrative, but the branch really is almost always empty, and a person beside it is what keeps the bird away.

Auto capture, added in firmware 2.00, hands the waiting to the camera. You frame the branch, describe what a worthwhile subject looks like, and step away. The camera watches the live picture, shoots a burst when something passes your tests, then pauses and watches again (p. 559). The photo shooting menu holds the stills version and the video recording menu holds a twin that records clips. Page numbers in parentheses point to Nikon's Z6III Reference Guide, edition 09, which matches firmware 2.00.

01.Who Decides When to Shoot

Three tools can fire a camera with nobody's finger on the shutter button, and they differ in who decides. A remote release, wired or radio, leaves the decision with a person at a distance, who still has to watch the branch. An interval timer hands it to a clock, which shoots every so many seconds whether or not anything is there, as Silent Shooting, Timers and Time-Lapse explains.

Run the kingfisher afternoon through an interval timer. One frame every 10 seconds for five hours is $18{,}000 / 10 = 1{,}800$ frames. Each visit catches about 2, so the afternoon yields roughly 8 frames of bird among 1,800. Auto capture shoots only while the bird is present. At 7 frames per second (fps), the rate Continuous H is held to during auto capture (p. 562), 80 seconds of bird can give up to $80 \times 7 = 560$ frames, nearly all with the bird in them. That assumes Recording time selection at OFF, no burst limit. With the 3-second bursts and 10-second pauses I suggest below, a 20-second visit allows two bursts of $3 \times 7 = 21$ frames, 42 in all.

To decide for itself, the camera needs something it can measure. Nikon offers three capture criteria: movement in chosen directions, a recognised kind of subject, and a subject inside a band of distances (pp. 559-560). Each turns "is that the bird?" into a pass-or-fail test that is cruder than your eye, and every problem in this chapter comes from that gap.

Every Ticked Test Must Pass

The tests combine by "and". Tick two criteria and the camera fires only when both pass together (pp. 560, 568). An unticked criterion is skipped, and its advanced settings have no effect (pp. 560-561).

"And" changes both kinds of error. Suppose, purely for illustration, that each of two tests recognises a real bird 90% of the time and that they fail independently. Both pass together $0.9 \times 0.9 = 0.81$ of the time, so a second test turns one miss in ten into nearly one in five. In general, if the ticked tests pass a real subject with probabilities $p_1, p_2, \ldots, p_k$ and fail independently, the chance of firing is their product:

$$P_{\text{fire}} = p_1 \, p_2 \cdots p_k$$

The same multiplication works for you against false triggers, because a gust must now fool every test. Nikon recommends one criterion at a time while you learn (p. 564), and the arithmetic agrees: add a second test only to stop a false trigger you have actually seen.

The Target Area Is a Mask

The criteria say what to look for. The target area says where. It divides the frame into a grid of points, and you switch off the points over parts of the frame that are blocked or not worth watching (p. 561), such as a bush that moves in the wind. A trigger can start only in or near an enabled point, and movement in a disabled point is ignored even with Motion ticked (pp. 561, 566). Nikon says this makes detection more accurate (p. 565).

Two limits come with it. The target area is offered only when the AF-area mode, the setting that decides where in the frame autofocus (AF) searches, is Auto-area AF, or when you focus manually (p. 565). In other AF-area modes you place the focus point where you expect the subject instead (pp. 562, 567). And target-area selection is unavailable whenever Distance is ticked (p. 566). Nikon prints that rule under a manual-focus caution, but the sentence names no focus mode, so I treat the two as either-or.

02.What Goes Wrong Unattended

False Triggers

The camera cannot tell a bird from a twig that moves like one. Nikon names falling snow, heat haze and other weather as possible triggers, and rain and snow as things that can disturb detection (p. 577). Wind is the everyday case. An object of height $h$ at distance $s$ from a lens of focal length $f$ forms an image about $h f / s$ tall when $s$ is much larger than $f$. A leaf 50 mm long, 8 m away at 600 mm, forms an image of $50 \times 600 / 8{,}000 = 3.75$ mm, about a tenth of the sensor's 36 mm width. That is the size of a small bird, so a size threshold alone cannot separate them. Masking the vegetation, or using Subject detection instead of Motion, is the stronger defence.

People are a trigger of their own. With Auto or People chosen as the subject type, auto capture begins when it detects a human figure, whether or not the person faces the camera (p. 574). A walker passing near the target area at a garden feeder can fire it, if large enough to clear the Smallest size setting (pp. 566, 574).

Missed Triggers

A subject that crosses the frame too quickly may not be detected (p. 571). With several subjects in the frame, the camera may fail to find one in the target area (p. 577). With Distance ticked and focus set by hand, a subject far out of focus can spoil the distance reading (p. 576).

Running Out

An unattended camera can also simply stop. Nikon asks for a fully charged battery, or one of its optional AC adapters, for uninterrupted shooting (p. 562) and prints no standby battery life. The display switches off after about three minutes without input while auto capture stays armed (p. 568). In heat, or after long use, the camera may end the run to avoid overheating (p. 577).

The card can be bounded. Let $r$ be the frame rate, $t_{\text{rec}}$ the burst length in seconds and $t_{\text{wait}}$ the pause after each burst. If something keeps the criteria satisfied all the time, such as a branch thrashing inside the mask, each cycle lasts at least $t_{\text{rec}} + t_{\text{wait}}$ seconds and yields $r \, t_{\text{rec}}$ frames, so an hour holds at most

$$N_{\text{hour}} = 3600 \times \frac{r \, t_{\text{rec}}}{t_{\text{rec}} + t_{\text{wait}}}$$

frames. With $r = 7$, $t_{\text{rec}} = 3$ and $t_{\text{wait}} = 10$, that is $3600 \times 21 / 13 \approx 5{,}815$ frames. Nikon lists a raw file, the sensor's data saved for later processing, at about 17.3 MB in the High efficiency★ format (p. 1012), so the hour could fill $5{,}815 \times 17.3 \approx 100{,}600$ MB, about 100 GB. With no pause and no burst limit the bound is $3600 \times 7 = 25{,}200$ frames an hour. RAW, JPEG, HEIF and Tone Mode counts about 23,700 such files on my 512 GB card, gone in $23{,}700 / 7 \approx 3{,}390$ seconds. These are rough bounds: card capacity varies with the scene (p. 1013), and Nikon does not say whether Custom Setting d2 Maximum shots per burst (p. 663), covered in Release Modes, Frame Rates and the Buffer, applies here.

03.Setting It Up

Before the Menu

Auto capture inherits several settings, so make them first. Fix the camera on a tripod after framing, and frame wider than usual while you learn, as Nikon suggests (p. 562).

Any continuous mode works: Continuous L, Continuous H or Continuous H (extended), or one of the four C modes from C15 to C120 (p. 562). Give Continuous L its rate, 1 to 7 fps, beforehand. Continuous H is fixed at 7 fps (p. 562), below the 8.1 fps it manages with d6 at Auto or Mechanical shutter (p. 154), and even 7 fps may sag when Custom Setting d6 Shutter type is Auto and the mechanical shutter is in use, or when d6 is Mechanical shutter (p. 562). Single-frame and self-timer modes switch to Continuous H at 7 fps for the run (p. 569). The guide gives no auto capture rate for Continuous H (extended).

The C modes are the high-speed frame capture family, which records JPEG pictures only (p. 464). With one chosen, Custom Setting d3 Pre-Release Capture options applies (p. 569), so frames from just before a trigger can be kept, as Pre-Release Capture explains. There a half-press fills the buffer, and Nikon does not say what plays that part here, so I cannot tell you how much history each trigger brings.

The image area must be FX, the full $36 \times 24$ mm sensor, or DX, a $24 \times 16$ mm crop, and not 1:1 or 16:9 (p. 562). Choose an AF-area mode and place the focus point where you expect the subject. With autofocus on, the camera switches to AF-C, the mode that keeps refocusing as the subject moves, for the run. In manual focus (MF), set the distance by hand first (p. 562). For a quiet run, turn on Silent mode in the setup menu before starting (p. 569).

The Photo Item and Its Presets

added in Firmware 2.00

The item has two entries, Set and Select user preset (p. 559). Settings live in five presets, User preset 1 to User preset 5, and the default is User preset 1 (p. 449). Choose the preset first, then Set, and what you adjust is stored there (p. 563). Pressing right on a preset opens View settings, Rename, up to 19 characters, and Copy. Selecting a saved preset and choosing Set runs it (p. 559).

Set opens the settings display with six items: Capture criteria, Advanced: Motion, Advanced: Subject detection, Advanced: Distance, Target area and Timing options (p. 560). In Capture criteria you tick Motion, Subject detection, Distance or any combination (p. 563). Nikon prints no defaults for these six items, so check each before a first run.

Motion

Advanced: Motion sets three things (pp. 570-572). First, the directions of travel that count, each ticked or unticked. Second, Slowest, from 1 to 5 on the sub-command dial, which excludes slower subjects. Nikon expresses it as the time to cross the frame horizontally, from about 5 seconds or less at 1 through 4, 3 and 2 seconds to about 1 second or less at 5 (p. 571). Third, Smallest, from 1 to 5 on the main command dial, which excludes subjects smaller than 4, 8, 14, 24 or 34 points (p. 572). Green boxes show what qualifies, and Nikon advises starting both at 1 and raising them gradually (p. 571).

The crossing time depends on lens and distance. The frame's width at distance $s$ is about $w = s \times 36 / f$ for the full sensor, so at 8 m and 600 mm, $w = 8 \times 36 / 600 = 0.48$ m. A bird hopping along a branch at an illustrative 0.2 m/s crosses that in $0.48 / 0.2 = 2.4$ s, which qualifies at Slowest 3 but not at 4. A bird flying past at 5 m/s crosses in about 0.1 s, the kind of subject Nikon warns may be missed (p. 571). The guide does not convert points into a share of the frame, so set Smallest by watching the green boxes.

Subject Detection

Advanced: Subject detection offers Auto, People, Animal, Vehicle and Airplanes, with no Birds type (p. 573). For autofocus, Nikon describes Animal as finding dogs, cats and birds (p. 127). The auto capture pages do not say theirs matches, so birds are likely but not promised. Smallest runs from 1 to 5 as a share of the angle of view: 2.5%, 5%, 10%, 15% and 20% or more (p. 574).

A robin-sized bird 140 mm long at 8 m and 600 mm forms an image of $140 \times 600 / 8{,}000 = 10.5$ mm, about 29% of the frame's width. Nikon does not say whether its percentage measures width or area. If area, and the bird stands an illustrative 70 mm tall, its image is about 22% of the height, so its box covers about $0.29 \times 0.22 \approx 6.4\%$ of the frame. Either reading clears 2 at 5%, and only the width reading clears 3 at 10%, so 2 is my ceiling at that distance.

With Motion and Subject detection both ticked, each keeps its own Smallest, the two are judged separately, and a subject must satisfy both (pp. 572, 574).

Distance

Advanced: Distance fires on a subject between two distances and keeps shooting while it stays in that band (p. 575). It works with Nikkor Z lenses, Nikon's lenses for the Z mount, and may not with others. Put the on-screen target on something at the near limit and press AF-ON to set Nearest, then on something at the far limit and half-press the shutter button to set Farthest (p. 575). The main and sub-command dials fine-tune them, except on Nikon's 58mm f/0.95 Noct (pp. 575-576). Nikon recommends values shown in white over those in yellow, and shows metres even when Distance units is set to feet. In manual focus, either button records the current focus position, so turn the focus ring first (p. 576).

Target Area

Target area shows the grid. Pressing OK disables the highlighted point, shown in red, and pressing again re-enables it. Other buttons enable or disable every point, tapping the monitor toggles $3 \times 3$ blocks, and the i button saves (p. 565).

Timing Options

Recording time selection sets the length of each burst: OFF, meaning no limit, or 1 second to 30 minutes. With a value set, shooting continues that long even after the subject leaves, though some settings can end it sooner (pp. 561, 566). Wait after shooting sets a minimum pause, from 0 seconds to 30 minutes, before shooting can begin again, even if the criteria are still met (pp. 561, 566). Nikon calls it the pause after each shot, which I read as each burst, though the guide does not define the word.

Checking, Scheduling and Starting

The i button opens the settings confirmation dialog, which lists the ticked criteria at top left (p. 566) and draws green boxes around detected subjects. Outside Auto-area AF you can move the focus point here, and if the boxes are wrong you go back and adjust (p. 567).

The DISP button sets a scheduled start. Choose Yes for Set start day/time, enter the date, hour and minute under Start day/time, and pick a Shooting duration of No limit, 1 hour, 2 hours or 3 hours. Check Time zone and date first, as Nikon asks (p. 567).

The video-record button starts the run from the dialog, or the schedule starts it (p. 568). My button map gives that button Starlight view (photo Lv) in photo mode, and Nikon does not say whether a reassigned button still starts the run. Test it at home first.

Watching, Pausing and Ending

While armed, "A-CAP" flashes in the control panel, the small top-plate screen, and a yellow border surrounds the display if no qualifying subject has been seen (p. 569). A red border appears when a subject is detected and while shooting (p. 568). During the run every control is disabled except a half-press and the DISP, video-record and delete buttons (p. 577). A half-press or DISP wakes a dark display (p. 568). The video-record button pauses the run and resumes it, and the delete button ends it (p. 577).

What Auto Capture Refuses

Auto capture refuses the focus limiter, electronic VR, the camera's digital stabilisation for video, bracketing, the self-timer, Bulb and Time exposures, HDR overlay, multiple exposures, focus shift, the interval timer and time-lapse video (p. 577). Pixel shift excludes it too (p. 558), as does USB streaming (p. 220). The focus limiter is Custom Setting a15, covered in Focus Limiter, Saved Positions and Manual Focus. Nikon says nothing about a lens's own focus-range switch, so I read the ban as the camera's limiter only. Long Exposure and Night, Focus Shift Shooting and Multiple Exposure, HDR Overlay and Pixel Shift cover the rest.

The Video Item

added in Firmware 2.00

The video item records clips under the same kinds of conditions and refers back to the photo pages (p. 621). Every image area is available, where stills accept only FX and DX, and electronic VR is not (pp. 609, 621). It has its own Select user preset, defaulting to User preset 1 (p. 579). Nikon does not say whether the two menus share presets, or how Recording time selection maps onto clip length, so set the video item up from scratch.

Keeping a Setup

Save/load menu settings writes both auto capture items' settings to a card with the other menus (pp. 861-862), as User Settings and Settings Files describes. Auto capture can also sit in the photo or video i menu (pp. 700, 746), though my i menu leaves it out as a once-an-outing setting. I rename presets instead, so User preset 1 becomes PERCH 600.

04.A Perch, a Nest and a Feeder

These are my starting points with the Nikkor Z 180-600mm f/5.6-6.3 VR on a carbon-fibre tripod, to adjust after watching the green boxes and the first test frames. They are not field results.

A perch. My usual perched-bird setup in Choosing an Autofocus Setup is a small Wide-area AF (C1) box with Birds detection. That setup has me at the camera steering the box onto a bird, whereas here the camera waits alone at an empty branch, where wind is the bigger risk. Auto capture itself runs in C1 too, with the box on the branch (pp. 562, 567), but Nikon offers the target area only in Auto-area AF or manual focus (p. 565), and I would rather mask the frame, so I disable every point except the block around the branch. The camera waits at the distance in effect when the run began (p. 577), and Auto-area AF chooses its own point (p. 125), so I focus on the empty branch with my C1 box and AF-ON first, then switch to Auto-area AF. With Custom Setting a6 AF activation at AF-ON only (p. 637), nothing should refocus before the run, though that is my inference, as Nikon does not say so. Depth of field, the zone that looks sharp, shows how much rides on that parked distance. A common approximation is $2 N c s^2 / f^2$, with $N$ the f-number, $c$ the largest blur still read as sharp, conventionally 0.03 mm on this sensor, $s$ the distance and $f$ the focal length. At f/6.3, 8 m and 600 mm:

$$\frac{2 \times 6.3 \times 0.03 \times 8{,}000^2}{600^2} \approx 67 \text{ mm}$$

A bird landing a hand's width off the parked distance is soft, and Nikon does not say whether focus catches up. I tick Subject detection alone, with Animal and Smallest at 1, then 2, and leave Auto and People unticked. Continuous H at 7 fps keeps raw files. For take-offs, C30 with the longest pre-release burst trades raw for whatever pre-release frames d3 keeps.

A nest. Only at a distance where the birds behave as if nobody were there, which is the point of a 600 mm lens. Silent mode switches to the electronic shutter and quietens the camera, though autofocus and aperture sounds can still be heard (p. 846). I set it before starting because the button that toggles it is locked during the run (p. 577). An adult sitting on eggs passes Subject detection constantly, so here I would tick Motion instead with Slowest at 3 or 4, which ignores a bird that barely moves and should catch an arrival in a ticked direction unless it is too fast (p. 571).

A feeder. Birds in the hedge behind a feeder pass every test the feeder birds pass. Distance, with Nearest just in front of the feeder and Farthest just behind it, can reject them, if the hedge sits far enough behind for a distance reading whose accuracy Nikon never states (p. 576), at the cost of the target area (p. 566).

05.Recommended Settings

At a feeder, swap Subject detection for Distance, and at a nest, for Motion with Slowest at 3 or 4.

06.Beginner Mistakes

Ticking every criterion on the first day. Each test multiplies the chance of a miss, and when nothing fires you cannot tell which test failed. Tick one, as Nikon advises (p. 564).

Skipping the rehearsal. The green boxes in the confirmation dialog show what the camera can see (p. 567). If no box appears around a stand-in, no bird will trigger it either.

Leaving the focus limiter on. Auto capture cannot run with it (p. 577), and it is part of my normal perched-bird setup. Switch it off first.

Leaving Recording time selection at OFF over a windy scene. A branch that never stops moving can keep the camera shooting at 7 fps until the card is full, within an hour on a 512 GB card. Set a burst length and a pause.

07.Related Chapters

• Pre-Release Capture: the C modes and d3, which auto capture uses.
• Release Modes, Frame Rates and the Buffer: every release mode, frame rate and the burst cap.
• Subject Detection: what each detection type recognises in autofocus.
• Focus Limiter, Saved Positions and Manual Focus: the limiter auto capture refuses.
• Silent Shooting, Timers and Time-Lapse: Silent mode and the interval timer.
• Choosing an Autofocus Setup: my perched-bird focus settings.
• Card Slots and File Handling: Overflow and card capacity.