# Exposure Calculator

Created by Kenneth Alambra
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Jun 05, 2023

This exposure calculator or exposure value calculator will help you determine the equivalent exposure value of your camera settings that will match your lighting situation, helping you take great photos.

Learn what exposure's definition in photography is, what "exposure value" is, and how to calculate the exposure value from your camera lens' aperture opening, ISO sensitivity, and shutter speed. If that sounds interesting, let's get started!

## What is the exposure value?

In photography, we want to make sure we get our subject in focus and under sufficient lighting so that we capture all the important details. Exposure value is a number that represents the lighting situation of a particular scene that we are trying to capture. The exposure value, or EV, ranges from positive values as high as 15 and above (for really bright situations) to as low as negative values like -9 and below (under extreme low-light situations). With that said, we can say that the exposure's definition (photography) tells us something about how much light our subject is exposed to.

When taking photos, we want our camera settings to match the exposure value of our scene, or else our photo will either be darker (underexposed) or brighter (overexposed) than it should be. You can find a table of approximate EVs for any lighting situation in the How to calculate the exposure value? section of this text.

## Factors that affect the exposure value

There are three factors that affect exposure value. These are aperture opening, shutter speed, and ISO sensitivity which we describe in more detail below.

#### Aperture opening

The aperture opening is the only place where light gets into the camera. Aperture settings come in values called the f-stop, or f-number, that range from values as low as f/1.0 (for large aperture opening) to as high as f/64 (for really small pinhole size aperture openings).

The larger the aperture opening is, the more light is allowed to enter. The smaller the aperture opening is, the lesser light is allowed to enter. The aperture opening also affects the depth of field of your photo, which we can think of as to how much of our image is focused and how much of our image is blurred. To see how exactly it changes depending on the aperture, check out the depth of field calculator.

#### Shutter speed

Another factor that affects the exposure value is the shutter speed. Since the film (for film photography) and the camera's sensor (for digital photography) are sensitive to light, the aperture opening is shut most of the time by what we call the shutter (not a very imaginative name...). By pressing the camera's shutter release button, the shutter opens over a period of time and then closes. The duration that the shutter is left open depends on the shutter speed of our camera.

The faster the shutter speed is, the less light that our film or sensor is exposed to. Shutter speed can be set to fractions of a second (for sports or action photography) to a couple of minutes (for long exposure shots, like when taking photos of the Milky Way or for creative blurry shots).

#### ISO sensitivity

As the light enters our camera, it goes straight to the film or sensor. The film or the sensor has a property called the ISO sensitivity, or ISO speed, which describes how much light it processes at a given amount of time. The ISO sensitivity can have a value of as low as 100 up to as high as 102400 (for some really high-end cameras).

The lower the ISO sensitivity is, the less sensitive the film is to light, and the more amount of light it needs to process an image. This means that we would either need to set a slower shutter speed (or longer exposure duration) or use a higher ISO sensitivity value for low-light situations to make our picture brighter. However, really high ISO sensitivity oftentimes sacrifices photo quality as the image tends to get noisy. It is therefore best to set the ISO speed to the lowest setting and just adjust it if needed to compensate for changes to the aperture opening size and the shutter speed.

These three settings work together to create a particular exposure value so we don't end up having a photo that is either underexposed or overexposed to light.

## How to calculate the exposure value?

As we have learned from the previous section, the exposure value depends on the aperture opening, the shutter speed, and the ISO sensitivity. From a mathematical point of view, the exposure value is expressed as the base-2 logarithm of the square of the aperture f-number time 100 divided by the product of ISO sensitivity and the shutter speed at ISO 100 setting, as shown below:

$\small \mathrm{EV} = \log_2 \left(\frac{100 \cdot\mathrm{aperture}^2}{\mathrm{ISO \cdot shutter \ speed}} \right)$

where:

• $\mathrm{EV}$ is the exposure value;

• $\mathrm{aperture}$ represents the f-number of the aperture like 2.8 for f/2.8;

• $\mathrm{ISO}$ represents the ISO sensitivity as in 100, 200, 400, and so on; and

• $\mathrm{shutter \ speed}$ is the shutter speed in seconds.

The EV from this equation tells us whether our camera settings will be optimal for the lighting situation of our scene. A positive exposure value of EV+15 is a sign that we can use our current camera settings in outdoor daylight conditions, while a negative exposure value of EV-7 allows us to capture photos in low light conditions, such as when capturing auroras or the Milky Way Galaxy.

As a reference, here is a table showing the relative exposure values of common lighting conditions. This table is very handy if you take pictures at various lighting conditions and you enjoy calculating your own exposure values using the equation given above. If the scenery you wish to capture is not listed in the table below, try a setting that results in an EV of a lighting situation that is visually similar to your target lighting situation.

EV

Type of lighting situation

-7

Deep star field or the Milky Way.

-6

Night under starlight only or the Aurora Borealis.

-5

Night under crescent moon or the Aurora Borealis.

-4

Night under half moon, or a meteor shower (with long exposure duration).

-3

Night under full moon and away from city lights.

-2

Night snowscape under full moon and away from city lights.

-1

Start (sunrise) or end (sunset) of the "blue hour" (outdoors) or dim ambient lighting (indoors).

0

Dim ambient artificial lighting.

1

Distant view of a lit skyline.

2

Under lightning (with time exposure) or a total lunar eclipse.

3

Fireworks (with time exposure).

4

Candle-lit close-ups, Christmas lights, floodlight buildings, fountains, or bright street lamps.

5

Home interiors at night, fairs and amusement parks.

6

Brightly lit home interiors at night, fairs and amusement parks.

7

Bottom of a rainforest canopy, or along brightly-lit night-time streets.

Floodlit indoor sports areas or stadiums, and stage shows, including circuses.

8

Store windows, campfires, bonfires, ice shows,

Floodlit indoor sports areas or stadiums, and interiors with bright fluorescent.

9

Landscapes, city skylines 10 minutes after sunset, neon lights.

10

Landscapes and skylines immediately after sunset, capturing a crescent moon using a long lens.

11

12

Open shade or heavy overcast, capturing half moon using long lens.

13

Cloudy-bright light (no shadows), capturing gibbous moon using long lens.

14

Weak hazy sun, rainbows (soft shadows), capturing the full moon using long lens.

15

Bright or hazy sun, clear sky (distinct shadows).

16

Bright daylight on sand or snow (distinct shadows).

17-19

Very bright artificial lighting.

20+

Extremely bright artificial lighting, telescopic view of the sun.

In camera settings, the EV is usually rounded to the nearest whole number to simplify things. In the next section of this text, let us consider a sample calculation to understand how to calculate the exposure value even more.

## How to use our exposure calculator?

Since calculating logarithmic functions also needs a special calculator, why not just use our exposure calculator? Using our exposure calculator is easy. All you have to do is choose the settings for the aperture f-stop, shutter speed, and ISO sensitivity. You can also solve for the other settings if you have a preferred exposure value.

Let's say you want to know the exposure duration at a specific aperture f-stop and ISO sensitivity to capture an image under an EV-7 exposure value. All you have to do is unlock a shutter speed variable by clicking on the padlock icon next to it. Then, select your aperture f-stop and ISO sensitivity, and input a -7 in the EV variable. Upon entering this value, the recommended shutter speed will then be automatically displayed.

## Sample calculation of the exposure value

Let's say we want to take a portrait photo of our friend while at the park. The weather is slightly cloudy and we saw there is a rainbow in the background that we also want to be in the frame. Suppose it is our last film and it has a fixed ISO 200 sensitivity. We want to know if setting the aperture to f/8 and the shutter speed to 1/500 seconds would match the lighting situation. Solving the EV, we have:

\small \begin{aligned} \mathrm{EV} &= \log_2 \left(\frac{100 \cdot\mathrm{aperture}^2}{\mathrm{ISO \cdot shutter \ speed}} \right) \\ &= \log_2 \left( \frac{100 \cdot 8^2}{200 \cdot \frac{1}{500} \ \text{seconds}} \right) \\ &= \log_2 \left( \frac{6400}{0.40} \right) \\ &= \log_2 (16000) \\ &= 13.96578428 \approx \text{EV} \ 14 \end{aligned}

Looking at our table from the previous section, we see that the exposure value for taking pictures of rainbows under a hazy sun is equal to $\text{EV} \ 14$, and our calculated EV is approximately equal to $\text{EV} \ 14$, we can now say that those settings are suitable for the lighting situation we have. π

## More photography math?

Ever wonder how much storage your photos and videos take up on your computer or memory card? You can check our image file size calculator and video file size calculator to learn more about them. We also have a time-lapse calculator for any tricky shots.

Kenneth Alambra
Aperture opening settings
Aperture f-stop
f/2.8
Focal ratio
Shutter speed settings
Shutter speed
1/500
Duration of exposure
sec
ISO sensitivity settings
Film or camera sensor's sensitivity
ISO 200
ISO value
Output
Exposure value (EV)
10.966
EV ~11 is suitable for taking photos of the sunset, during sunset, and just before the sun sets. π
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