The Exposure Triangle: The Key To The Perfect Photograph

Exposure TriangleCapturing the perfect shot in photography takes more than being in the right place at the right time (although that’s not a bad start). The best possible image is a result of balancing the most important factors in exposure: aperture, shutter speed and ISO. These three elements form what is commonly referred to as the Exposure Triangle.

Learning the properties of each element, as well as how they relate to and affect each other, is nothing less than essential knowledge when it comes to manual photography. This stream-lined guide provides all the info you need to know about exposure and, of course, the Exposure Triangle. Once you’ve learned the basics, put theory to practice with the help of this mastering exposure in digital photography course.

Exposure Defined

While “exposure” generally refers to the brightness of a photograph, it is actually the result of the three aforementioned elements: aperture, shutter speed and ISO. Exposure, ultimately, refers to the amount of light that is processed either by film or by digital sensors. This can feel like a juggling act at first, but the amount of time you spend doing trial-and-error will decrease drastically as you increase both knowledge and experience. Even still, experimentation is an integral aspect of photography, as in any art, so you will never want to adhere too strictly to “rules.”

The Exposure Triangle

First, let’s look briefly at each element and how it affects exposure:

  • Aperture: This controls the size of the lens opening that allows light into the camera. Think of the aperture as a dilating pupil.
  • Shutter Speed: This refers to the amount of time that light is permitted to enter the camera. The shutter is literally a trap-door that opens and closes at fixed periods.
  • ISO: ISO is the sensitivity of the film or digital sensor. This controls what is called the “noise,” or graininess of a photograph.

This is what the exposure triangle would look like if it could be displayed in a diagram:

Exposure Triangle


Before we get into relationships, I want to take a quick look at each of the three elements, beginning with aperture. We already know aperture controls the size of the lens opening. These sizes are referred to as f-stops, and this is a nice f-stop chart to help give you a better idea. There is an inverse relationship between f-stops and the size of the lens opening, which is to say, when the f-stop increased, the size of the opening decreases. Two common f-stops are 1.4 and 2.8; 1.4 will have a larger opening than 2.8.

The size of f-stops can be calculated, although this information is not exactly practical. When an f-stop doubles (f/2 to f/4), the area of the lens opening is decreased to one-fourth the original size. It might be easier to think about going the other direction: when an f-stop is halved (f/2 to f/1), the area of the lens opening quadruples, or is four times the size.

A wide aperture (f/2), is going to have a very shallow depth of field (for example, if you focus on a nearby object, other objects in the background will be out of focus) while a narrow aperture (f/22) will have a deep depth of field (if you are shooting a panorama, this will allow you to get everything in focus). Here’s a wonderful post on going manual on your DSLR and understanding aperture.

Shutter Speed

Shutter speed is the most intuitive of the three elements of the exposure triangle. Shutter speed is measured in seconds; one second (1/1) being a very slow speed and 1/1000 of a second being very fast. Slower speeds are generally used for things like low-light and nighttime settings (here are 20 tips for better night photography), or to add blur or movement to a photo (I’m sure you’ve seen photographs of waterfalls in which the water is slightly blurred as it falls). You can quickly master these techniques with a long exposure photography course. Faster speeds, of course, are used to capture fleeting moments, such as sports and wildlife, but faster speeds are also used in brightly lit situations. This page is very helpful in matching shutter speeds to apertures and explains how to read photography charts.


ISO, also refereed to as the “speed” of your film or digital sensor, controls light sensitivity. This is easy to change on digital cameras, but on film cameras you literally have to change the roll of film if you want to adjust ISO. By controlling the sensitivity, you are also controlling what is known as “noise.” Think of it as interference on television, which causes “snow.” Noise is more or less synonymous with graininess. A low ISO, which will in turn have low noise, is almost always preferred because it will produce the clearest photographs. This is actually a great chart on ISO, and it further elucidates the exposure triangle. You might wonder why you wouldn’t always use a low ISO, which brings us, finally, to how these three elements relate.


The relationships between these three elements are very simple. Once you understand the basics, the links I provided to various charts will give you some suggestions for where to start with your settings. After that, it’s entirely up to your experimentation.

The first half of this relationship is somewhat obvious. With a wider aperture, which lets in more light, you are going to need a faster shutter speed or your photos will be over-exposed (meaning they received too much light). Naturally, then, a smaller aperture will require a slower shutter speed. I might add that these are general assumptions; the brightness of what you are shooting will affect these settings, as well.

The second half factors in ISO. A narrow aperture or a fast shutter speed (again, generally speaking) requires a high ISO. This actually makes sense; you need “fast” film (i.e. a high ISO, or very sensitive film) if you are going to capture an image through a tiny lens opening. Conversely, when you have a wide aperture or a slow shutter speed, you are able to use lower ISOs and thus attain an image with less noise.

Deceptively Simple

In theory, it’s literally that simple. In practice, of course, it’s much more difficult. But practice makes perfect, and you can get on the fast track with this five-star course on shooting in manual mode in digital photography.