Calculate exposure value, f-number or exposure time from two known inputs, with exposure time in seconds, milliseconds, minutes or hours.

Related Calculators

Exposure Value Formula

The following formula is used to calculate an exposure value.

EV = log2 (N² / t)

Where EV is the exposure value
N is the f-number value
t is the exposure time/shutter speed (seconds)

Exposure Value Definition

Exposure Value (EV) describes an aperture and shutter-time combination: EV = log₂(N²/t), with t in seconds. This settings formula does not include ISO or measure scene brightness; interpreting a meter reading also requires its ISO setting.

EV is important because it helps photographers achieve accurate and consistent exposures in various lighting conditions.

By understanding and utilizing EV, photographers can capture images with the desired level of brightness and detail, enhancing the overall quality of their photographs.

The EV scale ranges from low to high numbers, with each increment representing a doubling or halving of light.

For example, at fixed scene brightness, increasing the settings EV by one halves exposure, while decreasing it by one doubles exposure. A camera’s exposure-compensation setting uses a different convention: +1 EV requests one stop more exposure. This allows photographers to easily understand the relationship between different exposure settings and make informed decisions when adjusting their camera settings.

By knowing the metered EV and its ISO setting, photographers can quickly determine the appropriate combination of aperture, shutter speed, and ISO sensitivity to achieve the desired exposure.

For instance, if the metered EV is low, indicating a low amount of light, photographers may need to open up the aperture, slow down the shutter speed, or increase the ISO sensitivity to capture enough light and avoid underexposure.

If the metered EV is high, indicating a bright scene, photographers may need to close down the aperture, increase the shutter speed, or decrease the ISO sensitivity to prevent overexposure and preserve details in highlights.

Example Problem

How to calculate an exposure value?

First, select Exposure value and enter the f-stop/f-number.
In this example, the f-number is 3.
Next, determine the total exposure time.
The exposure time for this example problem is measured to be 1.23 seconds.
Finally, calculate the exposure value.
Using the formula above, the exposure value is calculated to be:
EV = log₂ (N² / t )
EV = log₂ (3² / 1.23 )
EV ≈ 2.8713

FAQ

What is the significance of the f-number in photography?
The f-number, or aperture, plays a crucial role in photography as it controls the amount of light entering the lens and reaching the camera sensor. It also affects the depth of field, which determines the extent of the scene in focus. A lower f-number means a larger aperture, allowing more light to enter, which is useful in low-light conditions but results in a shallower depth of field.

How does shutter speed affect a photograph?
Shutter speed, or exposure time, determines how long the camera’s sensor is exposed to light. It affects the brightness of the image and can create effects such as motion blur or freeze motion. A faster shutter speed can freeze fast-moving subjects, while a slower shutter speed allows more light in, which is beneficial in low-light situations but may blur any movement.

Why is ISO sensitivity important in photography?
ISO sensitivity measures the camera sensor’s sensitivity to light. A higher ISO setting can brighten your photos in low-light conditions but may introduce noise or graininess. A lower ISO produces clearer, more detailed images but requires more light. Balancing ISO with aperture and shutter speed is key to achieving the desired exposure and quality.

How can understanding EV help improve photography?
Understanding Exposure Value (EV) helps photographers quickly adjust their settings to achieve the desired exposure level, especially in challenging lighting conditions. By knowing the EV of a scene, photographers can make informed decisions on aperture, shutter speed, and ISO sensitivity adjustments to capture images with the right brightness, detail, and depth of field, enhancing the overall quality of their work.