If you're new to photography, calculating exposure can be a little intimidating at first. But once you get the hang of it, it'll become second nature! In this article we'll go over how to calculate exposure and show you how to use this information in order to make better photos.


Exposure isn't as hard as it looks; it just takes math.

  • Exposure is the amount of light that hits your camera sensor.
  • It's important to understand how exposure works to get the best results.
  • Exposure is a combination of three factors: shutter speed, aperture and ISO.

In order to calculate your shutter speed, you need to know a few things matters such as the amount of light in your shot, what kind of camera you're using, what aperture setting you're using, etc.

In order to calculate your shutter speed, you need to know a few things matters such as the amount of light in your shot and what kind of camera you're using.

When we talk about exposure and how we can manipulate it on our cameras, we're really talking about how much light comes into the camera. When we open up our aperture (the holes that let light into your lens), more light enters; when we slow down our shutter speed (the amount of time that these holes remain open), less light enters. Think about what happens when you take a photo at night vs during the day: if there isn't much ambient light around, then it'll be harder for us to get an accurate exposure because not enough photons from outside will hit our sensor or film.


Calculating exposure is a process that helps calculate how long your shutter should stay open to get the most light into your camera and create an optimal photo.

Calculating exposure is a process that helps calculate how long your shutter should stay open to get the most light into your camera and create an optimal photo.

Exposure is a measure of how much light reaches your film or sensor. The more light, the better the exposure; the less light, the worse the exposure. Exposure is measured in f-stops: 1/8000s at f/4 gives you more light than 1/4000s at f8.


There are three factors that you can change to affect your photo exposure: ISO, shutter speed and aperture.

There are three factors that you can change to affect your photo exposure: ISO, shutter speed and aperture. The first, ISO, is the most basic factor.

ISO is how sensitive your camera's sensor is to light. In other words, it's how much light will gather on your camera's sensor when it takes a picture (and by extension, how bright or dark that image will be). More sensitive sensors need less exposure time and less light to produce the same image as a less sensitive sensor would require more exposure time and more light to produce the same result.


The second factor is shutter speed; this dictates how long "shutter" stays open during an exposure - thus letting more or less light in depending on its setting (fast = brighter images; slow = darker images). And finally there’s aperture which controls not only depth of field but also contributes indirectly towards effective shutter speeds thanks to its relationship with f-stops (which we'll get into later).


When you divide up this number into fractions, you get the increments of exposure -- so by dividing it in half each time you get f/4, then f/5.6, then f/8, then f/11 and so on ... until it's divided into 256 sections (or an F-stop number that is larger than your camera can shoot).

Let’s say you are using a camera with an ISO setting of 100. You can shoot at f/1.4 and 1/100th of a second, or f/2.0 and 1/500th of a second, or any other combination that adds up to the same exposure value (EV). The EV is determined by dividing your shutter speed by the length of time that light hits the sensor (or film). In other words: If you have one hour to take photos in low light conditions but only one-quarter of an hour left before sunrise, then you can either use a very small aperture like f/11 or use really long shutter speeds such as 15 minutes so that both scenarios will result in equal exposures despite drastically different lighting conditions.

You might have heard of something called "exposure compensation." This is a setting on your camera that allows you to adjust your exposure by -1, 0 or +1. For example, if you are shooting in low light conditions and want to get more light into your image (ie., decrease exposure), then this would be the setting used.