Release Modes, Frame Rates and the Buffer

A grey heron crouches at the water's edge with the 180-600mm already on it. Suppose its take-off lasts two seconds. In the camera's fastest raw burst, 20 frames per second (fps), that is 40 photographs. Nikon's largest raw files run to about 27.3 MB each (pp. 1012-1013), where an MB (megabyte) is a million bytes, so in those two seconds the camera makes

$$40 \times 27.3\ \text{MB} = 1{,}092\ \text{MB}.$$

While the memory card catches up, those frames wait in a block of fast memory inside the body called the buffer.

The release mode decides how many pictures one press of the shutter-release button makes and how quickly they come. The buffer decides how long that pace can last. Page numbers in parentheses point to Nikon's Z6III Reference Guide, edition 09, which matches firmware 2.00.

01.What the Release Mode Decides

The Release mode item chooses what a full press of the shutter-release button sets off: one picture, a stream of pictures that lasts while your finger stays down, or a countdown (p. 493). A new camera is set to Single frame (p. 447).

The quick route is to hold the release mode button and turn the main command dial, which steps through the modes. Turning the sub-command dial with the same button held picks the current mode's own option, such as the rate for Continuous L (p. 153). The item can also be placed in the i menu (p. 701).

A frame rate counts pictures per second, so its reciprocal is the gap between them. At 20 fps the gap is $1/20$ s, which is 0.05 s or 50 ms, where ms is a millisecond. At 8.1 fps it is $1/8.1 \approx 0.123$ s, about 123 ms. A wingtip or a dancer's foot travels a long way in 123 ms, and that difference is most of the case for the faster modes.

02.The Modes and Their Frame Rates

Single Frame

One full press makes one picture, and holding the button down adds nothing (p. 153), so every frame is chosen. Auto capture added in Firmware 2.00 borrows a burst even from this mode, switching to Continuous H at 7 fps while it runs (p. 569).

Continuous L

Continuous L shoots at a steady rate you pick, from 1 to 7 fps, for as long as the button stays down (p. 153). The rate is Custom Setting d1, which starts at 5 fps (p. 624). Its ceiling sits just under the 8.1 fps that Continuous H reaches with the mechanical shutter (p. 154), so treat it as the mode for rhythm rather than speed. With Photo flicker reduction on, this mode and Continuous H both put flicker handling first, so the display goes dark at every shot and the rate may slow or turn uneven (p. 483).

Continuous H

Continuous H is the everyday fast burst, and its rate depends on Custom Setting d6 Shutter type, which starts at Auto (p. 624). Auto switches between the mechanical shutter and the electronic front-curtain shutter (EFCS) according to shutter speed (p. 668). With Auto or the mechanical shutter the mode runs at about 8.1 fps, and with EFCS at about 10.5 fps. With the electronic shutter it reaches about 15.3 fps for NEF, Nikon's raw format, alone or with a JPEG, and about 16 fps for JPEG, the common compressed format, or HEIF (High Efficiency Image File Format) alone. Silent mode counts as the electronic shutter here (p. 154). What each shutter costs in distortion and flicker is the business of Shutter Types, Rolling Shutter and Flicker.

Continuous H (extended)

Continuous H (extended) is the fastest mode that records raw files: about 14 fps with Auto, the mechanical shutter or EFCS, and about 20 fps with the electronic shutter, for NEF and JPEG alike (p. 154). Nikon describes these as maximum rates from its own tests (p. 1000), so read them as ceilings.

The speed has costs. At some settings exposure may wander within a burst, and Nikon's remedy is autoexposure (AE) lock, held on the centre of the sub-selector (pp. 149, 155). The HLG tone mode, where HLG (hybrid log-gamma) is the camera's high-dynamic-range style that records HEIF files, pulls the rate back to that of Continuous H (pp. 155, 462). The mode keeps frame rate ahead of precise flash control whatever Custom Setting e8 says (p. 698), and ahead of Photo flicker reduction, which then darkens the display only for a burst's first frame and may fall short over a long burst (p. 483). This mode also keeps the display from going dark at each release, whatever the shutter (p. 679), which is why Custom Setting d15 exists, though d15's settings apply here only with the electronic shutter.

C15, C30, C60 and C120

The C modes make up high-speed frame capture + (HSFC+), which runs at 15, 30, 60 or 120 frames a second while the button is held, until the buffer fills or a time limit runs out. The limit is Post-release burst in Custom Setting d3 Pre-Release Capture options, which offers limits of 1 s, 2 s and 3 s as well as Max. The default, Max., lets shooting continue until the buffer is full, so the longest burst varies with the frame rate (pp. 154, 156, 624, 664-665). C15 is the newest of the four, added in firmware 2.00 added in Firmware 2.00.

They record Large JPEG files only, with quality set by a separate item, Image quality (HSFC), which offers JPEG fine or JPEG normal and starts at JPEG normal (pp. 157, 446, 464). C15, C30 and C60 accept FX, Nikon's full 36 mm by 24 mm frame, or DX, its smaller 24 mm by 16 mm crop, while C120 is DX only. The slowest shutter speed is 1/60 s, or 1/125 s at C120. Exposure compensation acts only between $-3$ and $+3$ EV, where an EV (exposure value) is one stop, and ISO sensitivity stops at ISO 64000 (p. 157).

They exclude flash, HLG, Photo flicker reduction and flexible program, along with features including bracketing, multiple exposure, HDR (high dynamic range) overlay, the interval timer, time-lapse video, focus shift and pixel shift (p. 157). Subject detection may suffer (p. 130), and the touch shutter takes single pictures only (p. 156). Nikon recommends a CFexpress or XQD card rated at 250 MB/s or more (pp. 157, 1011). These modes reach 1/16000 s (p. 157), a speed only the electronic shutter offers (pp. 668, 1000), so they must use it at least there, though the RG never names the shutter they use. The frames kept from before the press belong to Pre-Release Capture, and the readout behind these rates to What a Partially Stacked Sensor Changes.

Self-Timer

Self-timer delays the release, with its delay and shot count set in Custom Setting c2 (p. 158). It is covered in Silent Shooting, Timers and Time-Lapse.

03.The Buffer from First Principles

A Tank with a Tap and a Drain

The sensor finishes a frame far faster than the card can store it, so the camera parks each frame in its buffer, fast working memory between sensor and card, and the card empties it in the background.

Picture a tank with a tap above it pouring at the rate the camera makes data, and a drain below emptying at the rate the card writes. If the tap outruns the drain, the level rises. Once the level reaches the top, the tap can only run as fast as the drain, and in the camera that means the frame rate drops.

Start with toy numbers, chosen only because they divide neatly: a 1,000 MB buffer, 10 MB files, 10 fps and a card writing 50 MB per second (MB/s). Each second brings in $10 \times 10 = 100$ MB and takes out 50 MB, so the level climbs 50 MB a second. It reaches the top after $1{,}000/50 = 20$ s, by which time the camera has taken $20 \times 10 = 200$ frames.

In general, let $r$ be the frame rate in fps, $s$ the file size in MB, $w$ the write speed in MB/s and $B$ the buffer's size in MB. The level climbs at $rs - w$ MB/s, so the buffer is full after

$$t = \frac{B}{rs - w}\ \text{s}, \qquad N = rt = \frac{B}{s - w/r}\ \text{frames}.$$

The second form reads plainly. Each frame adds $s$ MB, and in the $1/r$ seconds before the next one the card removes $w/r$ MB, so each frame leaves $s - w/r$ MB behind. The toy case gives $1{,}000/(10 - 5) = 200$ frames again. If $w \ge rs$, nothing accumulates and the buffer never fills.

The model assumes that each frame takes exactly its file size in the buffer and that the card writes every file type at the same speed. Nikon states neither, so every result below, the ratios included, holds inside the model rather than as a measurement.

What the Camera Shows When It Fills

With the shutter-release button half-pressed, the frame counter shows how many more frames the buffer can take. When it is full the counter reads r000 and the frame rate drops (p. 155). Nikon calls the count approximate (p. 155). The slower rate is not printed, but the model predicts about $w/s$ fps, since a new frame fits only as the card frees room. For 17.3 MB files on a card writing 90 MB/s that is $90/17.3 \approx 5.2$ fps, an estimate rather than a Nikon figure.

The buffer also outlasts the button. After a burst the card access lamp can stay lit from a few tens of seconds to about a minute, the camera will not switch off until the buffer is saved, and a flat battery stops shooting while the waiting frames are written out (p. 155). Long spells of continuous shooting can also end on their own to prevent overheating (p. 915).

What Nikon Publishes, and What It Implies

Nikon publishes neither the buffer's size in MB nor the camera's write speed. It gives file sizes: about 27.3 MB for lossless compressed NEF, 17.3 MB for High efficiency★, which is the default (p. 446), 11.4 MB for High efficiency and 10.3 MB for a Large fine JPEG. It also gives a buffer capacity of over 1,000 frames for each of them (pp. 1012-1013). That capacity comes from a test in Continuous H (extended) with the electronic shutter, the FX area, SDR (standard dynamic range) and ISO 100, on a 660 GB Nikon CFexpress card, where a GB (gigabyte) is a thousand MB (pp. 1012-1013). The count may drop with Auto distortion control at ON, which is the default (p. 447), or with an optimal-compression JPEG option, the ones marked ★ (p. 1013). Nikon's online manual prints the same table.

Whatever the buffer's real size, the default d2 cap of 200 frames ends a 20 fps burst after 10 s, long before frame 1,000.

My Two Cards

My camera holds a Lexar Professional SILVER CFexpress 4.0 Type B 512 GB card in slot 1 and a Lexar Professional 2000x SDXC UHS-II 256 GB card in slot 2. SD (Secure Digital) is the smaller card family, and UHS-II (Ultra High Speed II) is its faster bus. The defaults make the CFexpress slot primary and set Secondary slot function to Overflow (p. 446), so every burst goes to the CFexpress card until it is full (p. 457), the same slot Nikon tested. A footnote on p. 1011 limits one Nextorage CFexpress 4.0 card to CFexpress 2.0 transfer speed in this camera. I expect the same of any 4.0 card, mine included, though the RG says it only of that card, and it does not say whether my Lexar matches Nikon's, so I claim no burst depth for it.

The SD card sets the drain once overflow reaches it, if it is made the primary slot, or under any Secondary slot function other than Overflow, since Backup, RAW primary - JPEG secondary and JPEG primary - JPEG secondary all write a copy of every picture to it (p. 457). In those cases I infer, though the RG does not say so, that a frame leaves the buffer only once its SD copy is written. Card Slots and File Handling covers the SD speeds and their sources.

A Worked Example on the SD Card

Take High efficiency★ files of 17.3 MB in Continuous H (extended) at 20 fps. Data arrives at $rs = 20 \times 17.3 = 346$ MB/s. The missing inputs are assumptions. The buffer is $B = 2{,}000$ MB, a round number of mine and not Nikon's. The write speeds bracket the SD card, both taken from the card-slots chapter: 90 MB/s, the sustained minimum that its V90 video speed class promises, and 260 MB/s, the most Lexar claims for it.

At $w = 90$ MB/s the level climbs at $346 - 90 = 256$ MB/s, so

$$t = \frac{2{,}000}{256} \approx 7.8\ \text{s}, \qquad N = \frac{2{,}000}{17.3 - 90/20} = \frac{2{,}000}{12.8} \approx 156\ \text{frames}.$$

At $w = 260$ MB/s it climbs at only $346 - 260 = 86$ MB/s, so

$$t = \frac{2{,}000}{86} \approx 23.3\ \text{s}, \qquad N = \frac{2{,}000}{17.3 - 260/20} = \frac{2{,}000}{4.3} \approx 465\ \text{frames}.$$

The faster card stretches the same buffer $256/86 \approx 3.0$ times, and that ratio holds whatever $B$ really is, because $B$ cancels when the two values of $N$ are divided.

Two points follow. Lossless NEF is $27.3/17.3 \approx 1.58$ times the size of High efficiency★, yet at 90 MB/s it gets 88 frames to the other's 156, a ratio of $156/88 \approx 1.77$, because the card's share is subtracted before dividing. And where $w \ge rs$, as 260 MB/s is for the two smaller files, the buffer never fills and the d2 cap ends the burst instead.

The same sum puts the C modes in proportion. Nikon's file-size table gives about 6.3 MB for a Large JPEG at JPEG normal, the HSFC default (pp. 1012-1013), so at C60 the inflow is $60 \times 6.3 = 378$ MB/s. That outruns both the 312 MB/s UHS-II ceiling from the card-slots chapter and the 250 MB/s card Nikon recommends for these modes (p. 1011), so the buffer fills whatever the card. Since a full buffer ends a C-mode burst, the model says a faster card lengthens it only a little.

04.What Changes Between Frames

Custom Setting a1 AF-C priority selection, where AF-C is continuous autofocus, defaults to Release, which fires every frame on schedule whether or not focus has caught up (pp. 623, 631).

Picture review waits for the burst to end and opens on its first frame (p. 222), and Series playback in the playback menu decides how bursts are grouped (p. 155).

05.The Custom Settings That Shape a Burst

CL Mode Shooting Speed

d1 sets the Continuous L rate, from 1 to 7 fps (p. 662), and starts at 5 fps (p. 624). Turning the sub-command dial while holding the release mode button changes it too (p. 153). For a portrait sitter, 3 fps gives a spread of expressions without a card full of near-copies.

Maximum Shots per Burst

d2 caps how many frames one press can take in a continuous mode, at 1 to 200 or at ∞, meaning no limit (p. 663). The default is 200 (p. 624). No limit works only with Electronic shutter at d6, and with any other shutter the cap stays at 200. In modes S and M at 1 s or slower, no cap applies at all (p. 663).

Outside the C modes, the cap ends a burst, whereas a full buffer only slows it (p. 155). I would keep 200, which at 20 fps is ten seconds of frames to sort and guards against a finger left resting on the button.

Sync. Release Mode Options

d4 matters only when this camera is the master of a group, linked through an optional wireless remote controller or the network menu's Connect to other cameras item (p. 666), with each camera saving to its own card (p. 396). Sync, the default (p. 624), fires the remote cameras whenever the master fires. No sync lets the master fire alone, which I infer from the choices the f2 Sync. release selection role offers under each setting (p. 709). With one body there is nothing to synchronise, so leave it at Sync.

Display On During Burst

ON, the default (p. 625), keeps the display live through a burst, and OFF blanks it (p. 678). The RG claims no benefit for OFF, and a blank viewfinder turns a moving subject into guesswork, so I leave it ON.

Release Timing Indicator

In the C modes and in Continuous H (extended) the display does not black out at each release, and d15 supplies a signal instead. In Continuous H (extended) it applies only with Electronic shutter at d6 (p. 679).

Indicator type offers Type A, a brief dark frame that Nikon says helps when panning, Type B, borders on all four sides, Type C, borders on the left and right only, and Off (p. 679). The default is Type B (p. 625). Type A auto restore delay sets a shutter speed, used in modes S and M, at or slower than which Continuous H (extended) switches to Type A regardless (p. 679). Its default is 1/6 s (p. 625), and the RG lists no other values. For birds I would try Type A, since panning is the case Nikon names, and keep Type B elsewhere.

06.Recommended Settings

For birds in flight with the Nikkor Z 180-600mm f/5.6-6.3 VR, I would choose Continuous H (extended) with Electronic shutter at d6, for about 20 fps of raw files and a 50 ms gap that catches both ends of a wingbeat (p. 154). Hold AE lock when the light is steady (p. 155). The take-off you react to late belongs to Pre-Release Capture. Outdoor dance in daylight takes the same settings.

For stage dance with the Tamron 70-180mm f/2.8 Di III VC VXD G2, I would choose Continuous H with the mechanical shutter or EFCS. Stage lighting can flicker, and Photo flicker reduction works with those shutters but not with the electronic one or in silent mode (pp. 483-484), though the rate may dip while it acts (p. 483). If the venue demands silence, the electronic shutter gives about 15.3 fps for raw (p. 154) without Photo flicker reduction, though High-frequency flicker reduction still works with it in modes S and M (p. 485), so check the early frames for banding.

For portraits with the Nikkor Z 85mm f/1.8 S, Continuous L at 3 to 5 fps, in bursts of two or three frames, catches the frame between blinks. For street and landscape, Single frame, because each frame is a decision.

07.Beginner Mistakes

Expecting 20 fps at the default shutter. Continuous H (extended) reaches it only with Electronic shutter. At Auto it runs at about 14 fps (p. 154).

Reading r000 as a fault. The buffer is full and the camera has slowed to the card's pace (p. 155). Ease off, or choose a smaller file.

Choosing HLG and losing the C modes. HLG locks them out and slows Continuous H (extended) (pp. 155, 462).

Changing Image quality in a C mode. Those modes read Image quality (HSFC) instead (p. 464).

08.Related Chapters

• Shutter Types, Rolling Shutter and Flicker: the d6 choice behind most frame rates.
• What a Partially Stacked Sensor Changes: the readout behind 20 fps and the C modes.
• Pre-Release Capture: d3 and the frames kept from before the full press.
• Silent Shooting, Timers and Time-Lapse: the self-timer and silent mode.
• Card Slots and File Handling: the cards that drain the buffer.
• RAW, JPEG, HEIF and Tone Mode: file sizes and HLG.
• Metering: AE lock.
• Settings Finder: every item with its path and default.
• Glossary: fps, buffer and release mode.