Exposure Modes

Two photographers stand on the same footbridge, aiming at the same weir. One shoots at f/8 and 1/125 s, the other at f/4 and 1/500 s. Side by side, the two files are equally bright, yet they are different pictures. In the first the far bank is sharp and the falling water is slightly softened. In the second the bank has dissolved into blur and the spray hangs frozen in mid-air.

Both made the same exposure and spent it differently. This chapter starts from the unit every exposure control counts in, moves on to the mode dial, which decides who spends the exposure, and ends with compensation and bracketing.

01.What a Stop Is

If the shutter stays open for 1/125 s instead of 1/250 s, the sensor receives twice as much light, because the light arrives at a steady rate for twice as long. Halve it again, to 1/500 s, and it collects a quarter of what it did at 1/125 s. Each doubling or halving is called a stop.

In general, $n$ stops multiply or divide the light by $2^n$, so three stops is a factor of 8 and five stops a factor of 32. Counting in stops turns multiplication into addition: two stops brighter, then one stop darker, is one stop brighter. The same unit has a second name, the exposure value or EV, and one EV is one stop.

On the Z6III, compensation, bracketing and the exposure indicator, a scale in the viewfinder and monitor that shows how far your settings sit from the meter's target, all count in EV, and by default each dial click is a third of a stop.

02.Aperture and the f-Number

A 50 mm lens whose opening is 25 mm across has an f-number of $N = 50/25 = 2$, written f/2. Close the opening to about 17.7 mm and the f-number becomes $50/17.7 \approx 2.8$. The area has halved, because area grows with the square of the diameter and $(25/17.7)^2 \approx 2$. So f/2 to f/2.8 is one stop.

The rule is that the light through the lens is proportional to $1/N^2$. Halving the light means multiplying $N$ by $\sqrt{2} \approx 1.414$, which explains the odd-looking sequence of full stops.

$1,\ 1.4,\ 2,\ 2.8,\ 4,\ 5.6,\ 8,\ 11,\ 16,\ 22$

Every second entry doubles, and the labels are rounded, so f/11 and f/22 are really about 11.3 and 22.6. A larger f-number means a smaller hole and less light. Third stops multiply $N$ by $2^{1/6} \approx 1.122$, giving the run from f/5.6 through f/6.3 and f/7.1 to f/8.

Aperture also sets the depth of field, the zone in front of and behind the focused subject that looks sharp. A larger f-number deepens it and a smaller one makes it shallow, which is the difference between the two footbridge pictures. On the Z6III the sub-command dial sets the aperture in modes A and M, within the range the lens allows (pp. 141, 142). On my Nikkor Z 180-600mm f/5.6-6.3 VR the widest aperture itself narrows from f/5.6 at 180 mm to f/6.3 at 600 mm, a third of a stop, and that matters for a custom setting later on.

03.Shutter Time

At 1/250 s the sensor gathers light for four milliseconds, and at 1/125 s for eight. The full stops of shutter time are a plain series of halvings, 1/1000, 1/500, 1/250, 1/125, 1/60 and so on. Third stops multiply the time by $2^{1/3} \approx 1.26$, which is where 1/400 s and 1/320 s come from between 1/500 s and 1/250 s.

These labels are rounded too: strict halving gives 1/128 s, not 1/125 s. Nikon notes that the 15 s and 30 s settings really last 16 s and 32 s, with marked and true times agreeing again from 60 s (p. 145).

Shutter time decides how motion is drawn: a short time freezes a running dog and a long one smears it. In S and M you can set anything from 1/8000 s to 30 s. Custom Setting d6 Shutter type chooses which shutter does the work, and at its default, Auto, the camera switches between the mechanical and electronic front-curtain shutters according to the speed (pp. 624, 668). Choosing the electronic shutter there opens speeds up to 1/16000 s, while the electronic front-curtain shutter stops at 1/2000 s (pp. 140, 668). Mode M goes further, to 900 s with d7 Extended shutter speeds (M), and offers Bulb and Time (pp. 142, 145). Long exposures have their own chapter in a later part of this guide.

04.ISO

Take a picture at f/8, 1/125 s and ISO 100, then another at ISO 200 with nothing else changed. The second is one stop brighter, although the same light reached the sensor both times. The third-stop values between run 100, 125, 160, 200.

Aperture and shutter time decide how much light the sensor collects. ISO decides how strongly the camera scales up the recorded signal. It adds brightness but never light, which is why high-ISO pictures look noisier, a subject for ISO and Auto ISO.

The Z6III runs from ISO 100 to 64000, with Lo settings to about ISO 50 and Hi settings to about ISO 204800 (p. 159). Hold the ISO sensitivity button and turn the main command dial to change it, and b1 ISO sensitivity step value chooses third-stop or whole-stop clicks (pp. 159, 652).

05.Exposure Value, Worked Through

Exposure value packs an aperture $N$ and a shutter time $t$ in seconds into one number.

$EV = \log_2 \frac{N^2}{t}$

For f/8 at 1/125 s, $N^2 = 64$, and dividing by $1/125$ means multiplying by 125, so $N^2/t = 64 \times 125 = 8000$. Since $2^{13} = 8192$, the result is a shade under 13, and the strict time of 1/128 s would make it exactly 13. A higher EV means less light reaches the sensor.

Opening one stop and halving the time cancel, so f/5.6 at 1/250 s lands on EV 13 as well. The table below runs six such pairs, and the small spread comes only from the rounded labels.

EV is conventionally quoted at ISO 100, and each doubling of ISO lets the same scene be shot one EV higher.

Here $S$ is the ISO setting and $EV_S$ the exposure value usable at that setting.

$EV_S = EV_{100} + \log_2 \frac{S}{100}$

At ISO 400 the shift is $\log_2 4 = 2$, so a scene needing EV 13 at ISO 100 can be shot at EV 15, such as f/8 at 1/500 s, where $64 \times 500 = 32000 \approx 2^{15}$. For the camera, this means the meter hands you a target brightness, not a setting. Any combination whose stops add up to it will do.

06.Many Roads to One Exposure

The figure below sets the three ladders side by side, one rung per stop. From f/8, 1/125 s and ISO 100, climb two rungs of aperture to f/4 and drop two rungs of shutter to 1/500 s, and the brightness is unchanged. Or climb one rung of aperture to f/5.6, drop three of shutter to 1/1000 s and climb two of ISO to 400. The net movement is zero each time.

Any move on one ladder can be cancelled by an opposite move on another, so one exposure is a whole family of settings. The members differ not in brightness but in side effects: depth of field from aperture, motion from shutter time, noise from ISO. Each mode on the dial fixes some rungs and lets the camera choose the rest, so choosing a mode is choosing which side effect you own.

07.The Mode Dial

Hold the mode dial lock release and turn the dial (p. 138). The photo/video selector decides whether the mode applies to stills or video (pp. 102, 107), and what follows describes stills.

AUTO

The camera sets aperture, shutter time and ISO, and takes over white balance and other choices too (p. 138). Items it controls are greyed out in the menus until you move to P, S, A or M (p. 139). AUTO suits handing the camera to a friend. It is a poor way to learn, because most of what the display shows is the camera's decision, though exposure compensation still works (p. 654).

P, Programmed Auto

The camera picks a shutter time and aperture from a built-in program, and ISO, white balance and the rest stay yours (p. 139). If it offers f/8 at 1/125 s, turning the main command dial moves to another pair with the same exposure, such as f/5.6 at 1/250 s. This is flexible program, a walk along two ladders in opposite directions. An indicator shows while a shift is in force, and it ends when you turn the dial back until the indicator goes, change mode, or switch off (p. 139).

S, Shutter-Priority Auto

You set the shutter time with the main command dial, from 1/8000 s to 30 s, or as fast as 1/16000 s with the electronic shutter, and the camera picks the aperture (p. 140). Use S when motion is the subject, such as 1/1000 s to freeze a cyclist or 1/15 s to soften moving water. The trap is the top of the aperture ladder. At 1/1000 s in a dim hall with an f/5.6 lens, the camera has no wider aperture to give, so with ISO fixed the picture comes out dark. Auto ISO, on at the factory (p. 446), solves this by climbing the ISO ladder instead.

A, Aperture-Priority Auto

You set the aperture with the sub-command dial and the camera picks the shutter time (p. 141). Use A when depth of field is the subject: f/1.8 on my Nikkor Z 85mm f/1.8 S to lift a face from a busy background, or f/8 to f/11 to keep a landscape sharp throughout. It is my default for portraits and landscapes. Watch the shutter time as the light fades, because with ISO fixed the camera keeps lengthening it.

M, Manual

The main command dial sets the shutter time and the sub-command dial the aperture, judged against the exposure indicator (p. 142). With ISO fixed the camera changes nothing when the light changes, which is what a studio or a matched series of frames needs.

Leave Auto ISO on in M, as it ships (p. 446), and you hold aperture and shutter time while the camera moves ISO to reach the exposure (pp. 145, 161). For birds, wildlife at dusk and stage work I use this, because shutter time guards against blur, aperture guards depth of field, and the only side effect left to the camera is noise. Setting its limits is covered in ISO and Auto ISO.

U1, U2 and U3

These positions store a snapshot of settings, including the mode, shutter time in S and M, aperture in A and M, a flexible-program shift and the compensation value (p. 142). Menus and Controls shows my set-up, and a later part on user settings covers saving them.

08.Exposure Compensation

Suppose the camera, in A at f/8, picks 1/500 s for a snowy field and the snow comes out grey. Add +1 EV of exposure compensation and it keeps f/8 but doubles the time to 1/250 s, one stop brighter. In S it would open the aperture a stop instead. Why the meter greyed the snow is for Metering.

Compensation moves the meter's target by a set number of stops, and the camera shifts whatever it controls to meet it. Positive values brighten and negative values darken. Note that the signs run opposite to the EV scale above: +1 EV of compensation lets in one stop more light, which is one EV lower on that scale.

Hold the exposure compensation button and turn a command dial. Stills take $-5$ to $+5$ EV and video $-3$ to $+3$ EV, in thirds unless the step size is changed (p. 151). The value shows in the control panel (p. 151). Return it to $\pm 0.0$ to cancel, because switching off does not reset it (p. 152).

M is the exception. With ISO fixed, compensation shifts only the exposure indicator, so shutter time, aperture and ISO stay put and the picture is unchanged (p. 152). With Auto ISO on, the camera changes ISO and the picture does change (p. 152). With a flash fitted, compensation alters both flash output and background (p. 152), and flash has its own later chapter.

The Exposure Indicator

In M the indicator shows whether the current settings would give a darker or brighter picture than the meter's target, and by about how much (p. 145). Centred means a match. Nikon's illustrations run from a third of a stop under to a reading off the scale beyond $3\tfrac{1}{3}$ EV over. The scale's divisions follow b2 EV steps for exposure cntrl, f8 Reverse indicators flips its sides, and the readouts flash when settings exceed what the metering system can handle (p. 145).

Step Size

Two third-stop clicks move $2/3$ EV, and two whole-stop clicks move 2 EV. b2 EV steps for exposure cntrl chooses the scale (p. 653).

1/3 EV (comp. 1/3 EV), the default (p. 624), gives thirds for shutter time, aperture, bracketing, and exposure and flash compensation. 1 EV (comp. 1/3 EV) moves shutter time, aperture and bracketing in whole stops while compensation stays in thirds (p. 653). Nikon's specifications also list half-stop steps for shutter time and compensation (pp. 1000-1001), though the Reference Guide does not name the menu option that selects them. Whole stops are easier to count but discard the two positions between rungs, and a third of a stop is a correction you will often want. Keep the default.

Easy Exposure Compensation

Compensation normally needs a button held while a dial turns. b3 Easy exposure compensation lets a dial do it alone in photo mode (p. 654).

On (Auto reset) lets a dial alone set it, and a value set that way clears at power-off or when the standby timer runs out. The standby timer is the idle period after which the camera switches its displays and meter off. On works the same but keeps the value. Off, the default (p. 624), needs the button. It applies in P, S, A and AUTO but not M, and the dial used depends on the mode (p. 654).

I leave it Off. A free dial will sooner or later be nudged by a thumb, and a whole sequence ends up a stop away from where you meant it. If you adjust compensation on nearly every frame, On (Auto reset) is the safer On, since a forgotten value clears itself.

Keeping Exposure When the Aperture Changes

On the 180-600 in M with Auto ISO off, set f/5.6, 1/2000 s and ISO 1600 at 180 mm, then zoom to 600 mm. The aperture narrows to f/6.3, and every frame is a third of a stop darker than planned. b7 Keep exp. when f/ changes makes up the difference (p. 658).

It acts only in M with Auto ISO off. As well as such zooms, it covers fitting a lens with a different aperture range and refocusing a micro lens (p. 658). Exposure maintenance off is the default (p. 624), and Shutter speed or ISO sensitivity name the setting the camera moves instead. Some lenses cannot be fully compensated, and it does nothing during video recording (p. 658).

For birds on the 180-600 I choose ISO sensitivity, because the shutter time is the setting I chose for a reason, and a third of a stop more ISO beats a slower shutter. On my constant-aperture Tamron 70-180mm f/2.8, zooming never changes the aperture, so it matters only when I swap lenses. In M with Auto ISO on, Auto ISO absorbs the change anyway.

09.Auto Bracketing

At a seaside sunset in A at f/8, the meter suggests 1/250 s. With bracketing at three shots and 1.0 EV, the camera takes 1/250 s, 1/500 s and 1/125 s: the meter's guess, a stop darker and a stop brighter. You keep the best or merge all three later.

Bracketing means stepping a setting either side of your best guess when there is no time to check each frame (p. 500). The Z6III can step exposure, flash level, white balance or Active D-Lighting.

Auto bracketing on/off starts and stops it. Auto bracketing set picks what varies: AE & flash bracketing for exposure and flash level, AE bracketing for exposure alone, Flash bracketing for flash level alone, WB bracketing and ADL bracketing. Number of shots and Increment shape the series, and Amount applies only to ADL (p. 500). Out of the box it is OFF, with AE & flash bracketing, 3F and 1.0 (p. 447).

Exposure Bracketing

With b2 at its default, the increment runs in thirds from 0.3 to 3.0 EV, and at 2.0 or more a series is capped at five shots (p. 502). At 0.3, 3F gives 0, $-0.3$, $+0.3$, and each larger setting adds a pair at the ends, reaching $\pm 1.3$ at 9F (p. 502). The display shows an icon, a progress indicator and the shots left (pp. 502, 503). Bracketing adds to any compensation, so $+0.7$ EV with a three-shot 1.0 series gives $+0.7$, $-0.3$ and $+1.7$ (p. 503).

What moves depends on the mode (p. 504). P varies shutter time and aperture, S the aperture, A the shutter time, and M the shutter time unless e6 says otherwise. With Auto ISO on, P, S and A move ISO only once out of range, while M varies ISO outright. With d7 on and a time beyond 30 s, M leaves the shutter alone (p. 504).

Continuous release pauses after each series, switching off part-way restarts the series rather than cancelling it, and each self-timer release fires the whole series (p. 504). Set Auto bracketing on/off to OFF to stop (p. 505). Flash bracketing needs i-TTL or qA flash control, the automatic modes in which the flash sets its own output (p. 504). The flash part of this guide explains both.

White Balance and ADL Bracketing

WB bracketing takes one exposure and writes several copies with different white balance, moving only between amber and blue (pp. 505, 507). Steps are in mired, a million divided by the colour temperature in kelvin, and one step is 5 mired. The increment is 1, 2 or 3 steps, and 3F at 1 gives the unaltered copy plus one a step towards amber and one towards blue (p. 506). It adds to white balance fine-tuning, is unavailable when image quality includes NEF (RAW), and blocks the shutter if the card cannot hold every copy (p. 507). RAW shooters can ignore it, as White Balance explains.

ADL bracketing varies Active D-Lighting across real exposures (p. 500). Two shots go Off then the Amount value. Three go Off, Low, Normal, four add High, and five add Extra high (pp. 508, 509). Continuous release again pauses after each series (p. 510). Active D-Lighting itself is in Picture Controls and Colour.

Bracketing in Mode M

In M at f/8 and 1/250 s with Auto ISO off, a three-shot 1.0 series runs 1/250 s, 1/500 s and 1/125 s at f/8. e6 Auto bracketing (mode M) chooses what moves when Auto ISO is off (p. 696).

For AE bracketing, Flash/speed varies shutter time, Flash/speed/aperture shutter time and aperture, Flash/aperture aperture and Flash/ISO sensitivity ISO, while Flash only leaves exposure alone. With AE & flash bracketing, each also varies flash level (p. 696). With Auto ISO on, the camera acts as if Flash/ISO sensitivity were chosen (p. 696). Flash/speed is the default (p. 625).

Keep Flash/speed. Frames for a merge should differ only in brightness, and a moving aperture changes depth of field between them. Bracketing ISO is worse, because every frame collects the same light, so the brighter frames gain no extra light and add little or no shadow detail, only the same signal scaled up with its noise.

Bracketing Order

By default three frames at 1.0 EV come out 0, $-1$, $+1$. e7 Bracketing order can make that $-1$, 0, $+1$ (p. 697).

MTR > under > over, the default (p. 625), takes the unaltered frame, then the darkest, then the brightest. Under > MTR > over runs darkest to brightest. Neither changes an ADL series (p. 697).

I prefer Under > MTR > over, because each series then reads as a dark-to-light ramp among thumbnails, so the sets are easy to separate when merging.

10.Recommended Settings

11.Beginner Mistakes

Leaving compensation dialled in. It survives switching off (p. 152), so last night's $-1.0$ EV for the stage darkens this morning's landscapes. Check the control panel before the first frame.

Using compensation in M with ISO fixed. It moves only the indicator (p. 152). Follow the indicator with the dials, or turn on Auto ISO.

Forgetting bracketing is on. Single frames cycle through normal, dark and bright, and bursts stop after every series (p. 504). Switching off does not cancel it, so set Auto bracketing on/off to OFF when done.

Expecting b7 everywhere. It acts only in M with Auto ISO off (p. 658). Elsewhere the camera already adjusts when the aperture changes.

Treating ISO as extra light. ISO brightens the file without collecting more light, which is why it costs noise. Open the aperture or lengthen the time first where the subject allows, then raise ISO.

12.Related Chapters

• Metering: how the camera measures a scene and sets the target every mode aims at.
• ISO and Auto ISO: noise, extended settings, and Auto ISO in every mode including M.
• Menus and Controls: the dials and buttons used here, and the U1 to U3 positions.
• White Balance: colour temperature and the fine-tuning WB bracketing builds on.
• Picture Controls and Colour: the look of processed pictures, including Active D-Lighting.
• RAW, JPEG, HEIF and Tone Mode: RAW, JPEG and HEIF, which decide whether WB bracketing is available.
• Glossary: short definitions of stop, EV, aperture and each mode.