Exposure value (EV) is one number that stands for every pair of aperture and shutter speed that lets in the same amount of light. It matters because it puts all light on one ruler, counted in stops: the clay hills above, at dusk, sit near EV 11, full sun near EV 15, a lit street at night near EV 6, a moonlit landscape near EV -3 to -2, and once you can place a scene on that ruler you can compare scenes, read a camera’s specifications and set an exposure without a meter.
Each step of 1 EV is one stop, a doubling or a halving of light. The rest is knowing which way the numbers run, what they are measured against, and how to use them to choose a picture rather than just a brightness.
Not sure why one stop means double the light, or how aperture, shutter and ISO each count in stops? Stop starts from there.
Two meanings of EV: a setting and a scene
Most EV confusion comes from one word used for two related things.
- Settings EV describes your camera: one aperture and one shutter speed. A higher settings EV is a smaller aperture, a faster shutter or both, so less light gets in. There is no ISO in it.
- Scene EV describes the light: the settings EV a scene needs for a correct exposure at ISO 100. A higher scene EV is a brighter scene. Some writers call this the light value (LV), or write it EV100, to keep it apart from settings EV.
The two run the same way once you see the logic. A brighter scene needs less light let in, so a bright scene (high scene EV) calls for settings that admit little light (high settings EV). When someone says “a sunny day is EV 15”, they mean that at ISO 100 a correct exposure of that scene needs settings worth EV 15, such as f/16 at 1/125 second.
The formula, and what it tells you
Settings EV is the base 2 logarithm of the f-number squared divided by the shutter time in seconds: EV = log2(N² / t). You rarely need to calculate it, but the definition gives you three anchors.
- EV 0 is f/1 at 1 second. Every other value is counted in stops from that point.
- Each whole number is one stop. Moving from settings EV 12 to EV 13 halves the light reaching the sensor; moving from EV 12 to EV 11 doubles it.
- Aperture counts by squares. Light through the lens depends on the area of the opening, so each full f-stop (f/2.8, f/4, f/5.6, f/8) is a factor of about 1.4 in the f-number and a factor of 2 in light.
One small honesty note. The f-numbers and shutter speeds marked on a camera are rounded. f/16 is really f/16, but f/5.6 is a rounded 5.66, and 1/125 is a rounded 1/128. So f/16 at 1/125 works out to EV 14.97, and f/5.6 at 1/125 to EV 11.94. Every EV quoted on this page, and in any table you will find elsewhere, is good to about a third of a stop for that reason alone, which is far finer than the scenes themselves vary.
One EV, many different pictures
Every EV covers a whole family of settings that give the same exposure. Open the aperture one stop and halve the shutter time, and the EV stays the same. Here is the family for EV 12, the light of a typical overcast day at ISO 100:
| Aperture | Shutter speed | What changes in the picture |
|---|---|---|
| f/2.8 | 1/500 s | Shallow depth of field, motion frozen |
| f/4 | 1/250 s | Soft background, most action frozen |
| f/5.6 | 1/125 s | Moderate depth, walking people sharp |
| f/8 | 1/60 s | Deep focus, fast movement starts to blur |
| f/11 | 1/30 s | Near to far sharpness, handheld shake risk |
| f/16 | 1/15 s | Maximum depth, water and crowds blur |
All six frames would have the same overall brightness. They would not look alike. This is the practical heart of EV: the scene fixes the exposure value, and your job is to choose where on that line to sit, trading depth of field against motion blur. ISO is the third lever. It does not change how much light arrives; it changes which settings EV the scene calls for, which slides the whole family up or down the scale.
What program mode is doing
Picture a grid with apertures across the top and shutter speeds down the side. Every pair with the same EV lies on one diagonal line through that grid. When your camera is in P mode, the meter finds the scene’s EV, which picks the diagonal, and a built-in rule called the program line picks one point on it, usually a shutter speed safe for handholding with a middle aperture. Turning the dial in P mode (program shift) slides you along the same diagonal: f/4 at 1/250 becomes f/8 at 1/60, same EV, different picture. Aperture priority and shutter priority are the same idea with you fixing one end and the camera finding the other. Camera modes covers each mode in detail.
Want to slide along one EV line and watch the picture change while the brightness stays put? The equivalent exposures tool on the exposure triangle page does exactly that, and the camera simulator lets you try it on a scene with moving subjects.
How bright is the world? Typical scene EVs at ISO 100
These values are widely used starting points for a correct exposure at ISO 100. Real scenes vary by a stop or so either way, but the spread from top to bottom is the useful part: it shows how wide the range of everyday light is.
| Scene | EV at ISO 100 | Example setting |
|---|---|---|
| Snow or pale sand in bright sun | 16 | f/16, 1/250 s |
| Typical landscape in full sun, distinct shadows | 15 | f/16, 1/125 s |
| Hazy sun, soft shadows | 14 | f/11, 1/125 s |
| Bright overcast, no shadows | 13 | f/8, 1/125 s |
| Heavy overcast, or open shade on a sunny day | 12 | f/5.6, 1/125 s |
| Just after sunset | 9 to 11 | f/4, 1/60 s (EV 10) |
| Neon signs and brightly lit shop fronts | 9 to 10 | f/2.8, 1/125 s (EV 10) |
| Stage shows, indoor sports arenas | 8 to 9 | f/2.8, 1/30 s (EV 8) |
| Offices and bright work spaces | 7 to 8 | f/2.8, 1/15 s (EV 7) |
| Night street scenes and window displays | 5 to 8 | f/2.8, 1/8 s (EV 6) |
| Home interiors at night, lamp light | 5 to 7 | f/2, 1/8 s (EV 5) |
| Floodlit buildings and monuments | 3 to 5 | f/2.8, 1 s (EV 3) |
| Landscape under a full moon | -3 to -2 | f/2.8, 30 s (EV -2) |
Notice the gap between a sunny landscape and a moonlit one: about 17 to 18 stops, a factor of more than 100,000. Even a well lit living room at night is roughly eight to ten stops darker than the street outside at noon, which is why indoor photos need so much more ISO or so much slower a shutter than your eyes suggest. Your eyes adapt; the sensor does not.
The top of the table is where the sunny 16 rule comes from: in full sun, f/16 at a shutter speed of 1 over the ISO. At ISO 100 that is f/16 at 1/100, about a third of a stop more exposure than EV 15. The rows below it trade that anchor down one stop for each step of dimmer light, by opening the aperture, slowing the shutter, or both.
The moon versus moonlight
One pair in that range catches almost everyone. The full moon itself is a sunlit landscape of grey rock, so it needs roughly the exposure of a sunlit scene on Earth: about EV 14 at ISO 100, give or take a stop, which is why the old “Looney 11” rule (f/11 at 1 over the ISO) works for photographing the moon. The landscape that the moon lights is a different matter. It is around EV -3 to -2, some 16 or 17 stops darker than the moon’s own face. Expose for the land and the moon blows out to a white disc; expose for the moon and the land goes black.
The photo above and the one at the top of this page show the same striped clay hills. The top one was made at dusk with the moon just up, at a scene EV of about 11. The one above was made after dark, at a scene EV of about 1. That is roughly ten stops apart, more than a thousand times less light, and yet both frames look properly exposed, because the settings, ISO included, moved by the same ten stops. Even the after-dark frame is several stops brighter than a landscape lit only by the full moon, which suggests some glow was still left in the sky.
A brightness ladder from the photos on this page
You can put any photo on the EV scale from its settings, and doing it for real pictures is the fastest way to build a feel for the numbers. The method has two steps. First, settings EV = log2(N² / t). Second, subtract one stop for each doubling of ISO above 100 (or add one for each halving below it) to get the scene EV at ISO 100.
| Photo on this page | Settings | Settings EV | ISO correction | Scene EV at ISO 100 |
|---|---|---|---|---|
| White dunes in bright sun | f/11, 1/90 s, ISO 50 | 13.4 | +1 | about 14.4 |
| Clay hills and rising moon at dusk | f/11, 1/80 s, ISO 400 | 13.2 | -2 | about 11.2 |
| Small town street after dark | f/2.8, 1/80 s, ISO 800 | 9.3 | -3 | about 6.3 |
| Niagara Falls under floodlights | f/14, 6 s, ISO 800 | 5.0 | -3 | about 2.0 |
| Clay hills under moonlight | f/2.8, 1/2 s, ISO 800 | 4.0 | -3 | about 1.0 |
Most land within a stop or so of their row in the scene table. The moonlit hills are the exception, three or four stops brighter than the full-moon row, for the reason given above. Where a photo does not match the scene you remember, the gap is information: a lingering glow in the sky, a brighter light nearby, or an exposure the photographer deliberately pushed brighter or darker for effect. A scene EV worked out from a photo always assumes the photo is “correctly” exposed, and the photographer gets to decide what correct means.
Converting EV to your ISO
Scene EVs are quoted at ISO 100 so everyone uses the same scale. ISO 100 is a convention, not a special or better setting. When you shoot at a different ISO, add one to the scene EV for every doubling of ISO above 100 to find the camera settings you need.
| ISO | Add to the ISO 100 EV |
|---|---|
| 50 | -1 |
| 100 | 0 |
| 200 | +1 |
| 400 | +2 |
| 800 | +3 |
| 1600 | +4 |
| 3200 | +5 |
| 6400 | +6 |
Worked example, night street. A lit street at night is around EV 7 at ISO 100. At ISO 1600 you add 4, so you need settings worth EV 11. At f/2.8 that is about 1/250 second, fast enough to freeze pedestrians. At ISO 100 the same street would need 1/15 second at f/2.8.
Worked example, moonlight. A landscape under a full moon is around EV -3 at ISO 100. At ISO 3200 you add 5, giving EV 2. At f/2.8 that is about 2 seconds on a tripod. At ISO 100 it would be more than a minute.
It works in reverse too. The street above was shot at f/2.8, 1/80 second and ISO 800. That is about settings EV 9.3; subtracting 3 for ISO 800 gives a scene of roughly EV 6 at ISO 100, right in the night street row of the table. Raising the ISO three stops did not add any light to that street. It let the camera use settings that admit three stops less, here a shutter fast enough to hold the car’s lights steady.
The sign problem: EV versus exposure compensation
This is where most people get tangled. Cameras label exposure compensation in EV, and +1 EV of compensation makes the picture brighter. Yet a higher settings EV means less light and a darker picture. Both are correct, because they describe different things.
- Exposure value is a position on a scale. Higher settings EVs are smaller apertures and faster shutters, so less light.
- Exposure compensation is a change to the exposure the meter suggested, counted in EV-sized steps. Plus means more light on the sensor; minus means less.
So +1 EV of compensation actually moves the camera to settings one EV lower. If the meter wants f/8 at 1/125 (EV 13) and you dial in +1, the camera shifts to something like f/8 at 1/60 (EV 12). The simplest way to keep this straight: when talking about compensation, brackets or dynamic range, read “EV” as “stops”. When talking about a setting, a bigger number means less light; when talking about a scene, a bigger number means more.
Wondering when to dial in plus or minus, and how much? Exposure compensation works through the scenes that fool a meter and the corrections that fix them.
EV in real light units
Scene EV is a measure of light, so it converts to the units a light meter or a phone light-meter app shows. For light falling on a scene, a commonly used conversion is lux = 2.5 × 2EV at ISO 100. Meter makers use slightly different calibration constants, so treat the results as good to about a third of a stop.
| Scene EV at ISO 100 | Light falling on the scene | Roughly like |
|---|---|---|
| 15 | about 82,000 lux | Full sun |
| 12 | about 10,000 lux | Overcast daylight |
| 7 | about 320 lux | An office |
| 5 | about 80 lux | A lamp-lit living room |
| 0 | 2.5 lux | Late twilight |
| -3 | about 0.3 lux | Full moonlight |
Each step down the scale halves the light: 82,000 lux halved three times is about 10,000. This is a useful check on the scene table. An office lit to a few hundred lux really does sit at EV 7 to 8, which is why indoor work at ISO 100 drops you to shutter speeds no one can hold steady.
Measuring a scene’s contrast in EV
EV also measures the difference between parts of one scene. With spot metering, point the spot at the brightest area you want to keep detail in and note the reading, then at the darkest area you want detail in. Subtract one from the other and you have the scene’s contrast in stops. A sunlit wall reading EV 15 and a shaded doorway reading EV 9 is six stops, a brightness ratio of 64 to 1.
Compare that number with what your camera can hold. A sensor with 12 stops of dynamic range can record a brightness ratio of about 4,000 to 1 in one frame, but in practice the clean, detailed part of that range is narrower, especially in the shadows. If the scene’s spread is close to or beyond what the sensor holds, you have three choices: give up detail at one end, add light to the shadows, or shoot several frames.
Set a scene’s contrast in stops against a sensor’s range below, and watch what clips at each end and how many bracketed frames it takes to hold it all.
EV in camera specifications and in your files
- Metering range, often written as something like “EV -3 to 20 at ISO 100”, tells you the dimmest and brightest scenes the camera’s meter can measure accurately. EV -3 is moonlit landscape territory; EV 20 is far brighter than any ordinary scene, so the top end rarely matters.
- Autofocus sensitivity uses the same scale. A focusing system rated to EV -4 can find focus in light darker than a full-moon landscape. These ratings are measured with a stated lens aperture, often f/2 or faster, so with a slower lens the real limit is higher. The more negative the number, the better it copes in the dark.
- Dynamic range is quoted in EV or stops, meaning the number of doublings between the darkest and brightest tones a sensor can record.
- Stabilization is rated in stops of shutter speed. A four-stop system claims you can hold the camera steady at four stops slower than you otherwise could, for example 1/4 second instead of 1/60.
Your photos carry EV too. The EXIF data in most camera files stores aperture and shutter speed twice: once as ordinary numbers, and once in an older system called APEX, where each setting is already counted in stops. In APEX, an aperture value (Av) of 6 is f/8 and a time value (Tv) of 7 is about 1/125, and Av plus Tv gives the settings EV, here 13. Some older cameras even had an EV ring on the lens that locked aperture and shutter together, so turning one moved the other along the same EV.
EV steps in bracketing and ND filters
Bracketing settings are written as EV offsets. A three-frame bracket at ±1 EV gives one frame at the metered exposure, one a stop darker and one a stop brighter. For merging into a high dynamic range image, the spread you need comes straight from the contrast you measured: three frames at ±2 EV add about four stops to what a single frame can hold, and five frames at ±2 add about eight.
Neutral density filters are sold with several naming systems, and all of them map to EV reductions:
| Filter factor | Optical density | Light reduction |
|---|---|---|
| ND2 | 0.3 | 1 EV |
| ND4 | 0.6 | 2 EV |
| ND8 | 0.9 | 3 EV |
| ND64 | 1.8 | 6 EV |
| ND1000 | 3.0 | about 10 EV |
Each 0.3 of density is one stop, and the filter factor is 2 raised to the number of stops. To use one, lengthen the shutter by the filter’s EV reduction in stops. A 1/125 second exposure behind a 10-stop filter becomes about 8 seconds, because ten doublings of 1/125 is 1024/125, a little over 8.
Try the arithmetic on a bright waterfall: put an ND filter of 6 stops or more on the lens, find a shutter of 2 seconds or longer, and keep the exposure correct.
Equal EV means equal exposure on a digital sensor at any shutter speed. Film is different: past about a second, most films need more exposure than the arithmetic says, an effect called reciprocity failure, so long film exposures need a correction from the film’s own data.
Need the shutter speed for a 6 or 10 stop filter without counting doublings? The exposure calculator does the arithmetic for any filter strength.
Estimating exposure without a meter
Knowing a handful of scene EVs lets you set a camera by eye, check a meter that seems wrong, or work with an old camera that has no meter at all. The method is short:
- Identify the scene from the table and pick its EV at ISO 100.
- Add the ISO correction for the ISO you are using.
- Pick the aperture you want for depth of field.
- Count stops to find the shutter speed. Start from f/16 at 1/125 for EV 15 and move one stop for each EV of difference.
- Check the histogram after the first frame and adjust by whole stops.
This also explains why reflected-light meters get fooled. A meter assumes the scene averages to middle grey. Point it at a sunny snowfield and it reads a high EV, perhaps 17 or 18, and the picture comes out with grey snow; point it at a black cat and it overexposes. EV is not middle grey and is not the meter’s target. It is just the ruler the meter’s answer is written on. When the meter’s reading disagrees with the table by more than a stop on a very light or very dark subject, trust the table and add compensation. A grey card or an incident meter avoids the problem by measuring the light rather than the subject.
Want to know why a meter aims for grey, and which metering pattern is least fooled? Metering explains how the camera measures a scene in the first place.
Common mistakes with exposure value
- Reading a higher settings EV as more exposure. On the settings scale, higher means less light. Only compensation and bracketing use plus to mean brighter.
- Thinking one EV up doubles the light. One settings EV up halves the light admitted. A scene one EV higher has twice the light, which is why it needs the halving.
- Quoting an EV without saying which kind. A scene EV is only meaningful with its ISO, normally 100. A settings EV has no ISO in it at all. Say which one you mean.
- Believing ISO changes how much light arrives. It does not. It changes which settings EV a scene calls for. The light on the sensor is set by aperture and shutter alone.
- Treating table values as exact. They are starting points, accurate to about a stop. Take a test frame and check the histogram.
- Assuming equal EV means an equal picture. Same brightness, different depth of field and motion. Choose the combination for the picture you want.
- Exposing a moonlit landscape like the moon. They are about 16 stops apart. The Looney 11 settings that suit the moon’s face leave the land almost black.
Try this: guess the EV in five places
You need ten minutes, a camera, and a notebook or your phone’s notes. Set the camera to aperture priority at f/4 with ISO fixed at 100 (turn auto ISO off). At f/4, settings EV is 4 plus the number of shutter doublings, which gives you a lookup you can carry:
| Shutter at f/4, ISO 100 | Scene EV |
|---|---|
| 1/1000 s | 14 |
| 1/250 s | 12 |
| 1/60 s | 10 |
| 1/15 s | 8 |
| 1/4 s | 6 |
| 1 s | 4 |
- Pick five places: full sun, open shade, a room lit by a window, a room lit by a lamp, and the darkest corner you can find.
- In each place, before you look at the camera, write down your guess of the scene EV from the table earlier on this page.
- Half press the shutter on an average subject, such as a wall in the light, not a white sheet or a black coat, and write down the shutter speed the camera chose. Read its EV off the lookup, counting one EV for each step in between.
- Write the difference between your guess and the camera’s answer.
You do not need sharp photos for this; you are only reading the meter. Judge the result like this: if most of your guesses land within one stop, you can already estimate exposure by eye. If they are consistently off in one direction, notice which; a common pattern is guessing interiors far brighter than they are. With a phone, use a camera app that shows shutter speed and ISO, then work out the settings EV from its fixed aperture and subtract the ISO correction.
Want to check you can count stops and trade them under pressure? Try the advanced exposure quiz on stops, ETTR and Manual mode.
Exposure value questions
Is EV the same as a stop?
A change of 1 EV is the same size as one stop. EV itself is a position on a scale, while a stop is a step along it, so “EV 12” names a place and “one stop brighter” names a move.
Why are scene EVs given at ISO 100?
So scenes can be compared on one scale. A scene needs different settings at different ISOs, so the reference is fixed at ISO 100 by convention and you add the ISO correction yourself. A settings EV, the aperture and shutter pair on its own, has no ISO in it.
Can EV be negative?
Yes. A negative scene EV means a scene darker than one that needs f/1 for 1 second at ISO 100. Moonlit landscapes and starry skies away from towns sit below zero.
What does “+0.3 EV” mean on my camera?
One third of a stop brighter than the meter’s suggestion. The display rounds 1/3 to 0.3 and 2/3 to 0.7, so +0.7 is two thirds of a stop and +1.0 a full stop.
Is EV the same as LV, or light value?
They count in the same steps. LV is a name some photographers use for scene EV at ISO 100, to keep the brightness of a scene apart from the camera settings that suit it. A scene of LV 12 needs settings of EV 12 at ISO 100, EV 13 at ISO 200, and so on.