Exposure Triangle

Aperture, shutter speed, and ISO all work together to create a properly exposed image.

The exposure triangle is a relatively new term first bursting onto the scene somewhere between 2005 and 2010. Before that, it was “time + intensity = exposure.” With digital cameras and their ability to change ISO values, that old mentality went out the window.

The exposure triangle, in my opinion, is meant to teach the concept of equivalent exposures. Assuming that you already have a properly exposed image, when you adjust one setting, you need to adjust something else in an equal, but opposite way.


What makes up the exposure triangle?



Aperture is just a hole that lets light hit some sort of recording medium (film, plate, sensor, etc.). They can be mechanical, like those found in modern lenses or leaf shutters. Or, they can be a simple hole, like those found in pinhole cameras. 

Apertures limit the amount of light which can reach a sensor by increasing or decreasing the size of the hole. Changing the size of the hole will also change the depth of field. (visit the Aperture page for a more in-depth understanding of aperture)

Shutter Speed

A shutter controls the amount of time that light is entering the camera. Like an aperture, a shutter can be extremely simple, like using your hand to cover the lens or a pinhole. Or, they can be very complex like leaf shutters.

All shutters limit the amount of light entering the camera by blocking and unblocking the light entering the camera. Shutter speed also dictates the amount of motion blur present in the final image. (visit the Shutter Speed page for a more in-depth understanding of shutter speed)


In broad terms, ISO is the sensitivity of the recording medium. The higher the number, the more sensitive the medium.

Unlike film, digital ISO can be changed with each photo. However, like film, the high you set your ISO, the worse the image quality will be. As you go up the ISO scale you will notice grain or noise, especially in the shadows.

Generally speaking, you should use the lowest ISO possible which produces the desired aperture and shutter speed settings. (visit the ISO page for a more in-depth understanding)

Why is it important?

The exposure triangle tells you nothing about what the proper exposure for a photo should be. So what makes it important?

The exposure triangle is all about equivalency. Equivalent exposures are when your photos from the same scene have the same brightness (or density if you’re using film). It is when you change one leg of the triangle, like decrease the aperture, and make up for the loss of light by increasing the ISO or decreasing your shutter speed.

Equivalent exposures become important as you look to control your depth of field through changes in the aperture, motion blur through changes in the shutter speed, or control noise with changes in ISO. Knowing that you have to make an adjustment in the other direction (more or less light/sensitivity) becomes very important to your creative process.

Shutter Speed

Shutter speed, along with aperture and ISO, is part of the exposure triangle. Shutter speeds are almost always written in seconds or fractions of a second.

There are a few main types of shutters, which are covered in the shutter section. They all function slightly differently but their main goal is to control the length of time light is falling on the sensor, film, or recording medium.

Just like learning to control the aperture is part of the photographic process, learning how shutter speed impacts your photos is equally important.






Shutter Speeds Help Control Motion

Shutter speeds control how much motion blur is present in a photo. Motion blur comes in two different varieties. Camera shake is accidental motion blur caused by the person holding the camera at a slow speed. Intentional blur is when you decide to use settings that either impart blur into the photo or freeze motion; it’s purposeful.

Camera Shake


Camera shake is a fairly easy problem to solve. In order to remove camera shake, increase the shutter speed and compensate by changing your ISO or aperture. A good rule of thumb is to follow the 1/focal length rule. That means that, usually, as long as you are shooting faster than whatever your focal length is, your photo will be acceptably blur free. As an example, if I am using a 200mm lens, I would try to avoid shooting under 1/200th of a second while hand holding.

Newer lenses and bodies may have stabilization aids built into them. From what I have seen, they always measure the effectiveness of the stabilization in terms of stops. That means that you can shoot hand-held at however many stops the images stabilization is rated for. For example, a 300mm lens with two stops of stabilization should be able to be hand-held down to 1/80th of a second. (In practice, I have not found this to be true on larger lenses which are excessively heavy.)

Some manufacturers claim that using a lens with image stabilization on a body with sensor stabilization allows you to stack the stabilization. So, a Nikon lens with two stops of stabilization mounted on a camera with three stops of stabilization abilities could theoretically give you five stops of stabilization. That would mean that same 300mm lens with two stops of stabilization would be able to be hand held at 1/10th of a second! (Again, I doubt the effectiveness in longer or heavier lenses)

Another way to avoid camera shake is to use a monopod or tripod when shooting at slow speeds. Tripods are usually more stable than monopods. Quality tripods are usually rated in weight. Generally, buying a tripod that can support twice the weight of your camera will provide you with the sturdiness that you need in the max taxing situations.


Intentional Blur

Learning to control blur will give you another tool to create impactful images throughout your photographic career. “Controlling” in this sense does not mean to freeze all the action all the time but rather learning techniques to freeze motion or blur objects and people. Knowing when to use a method is dependent on the look that you are trying to achieve.

We will be covering three major areas of motion blur in class. The first is long-exposure blur where the shutter is open excessively long, allowing an object’s motion to be appear as blurry. The second is frozen motion where an object appears frozen in time. The third is zoom blur which will give an object the appearance of exploding into view.

Long Exposure

Long exposures happen when the shutter is open long enough to capture some sort of motion caused blur. It could be a multiple minute long exposure meant to catch clouds streaking across the sky. Most firework photos are taken with five to 30 seconds of exposure. Or, maybe you’re trying to show the motion of dirt flying off a rally car and “slow” your shutter speed down to 1/250th.

Long shutter speeds can also be used to pan along with the subject. Doing this will blur the background of the image while isolating the movement of the subject.

Frozen Motion

Frozen motion is caused by having a sufficiently fast enough shutter speed to prevent blur from being recorded.

In all instances involving a mechanical shutter, the faster the object is moving, the faster your shutter speed will need to be in order to create photos which have no blur. In other words, it will take a faster shutter speed to stop the motion of a hummingbird’s wings than a manatee swimming.

Also, in general, the farther away an object is, the slower the shutter speed can be in order to stop the motion (this assumes that all other things are being held constant). This is due to the angular distance needed to travel in order to produce visible motion blue. So, pretend that I am photographing two identical planes at the same time, one of which is a mile away, the other of which is two miles away. The plane closest to me will travel a longer angular distance than the farther plane so I would need a faster shutter speed to stop its motion than I would for the farther plane. (see illustration)

Zoom Blur

Zoom blur occurs when you change the focal length of the lens (zoom in or out) while the shutter is open. Your shutter speed must be slow enough to allow you time to operate the zoom ring in order to utilize this technique.

Focus racking is a slightly different technique than zoom blur but the concept is the same. Your shutter speed just has to be slow enough to rotate the focus ring. This technique is frequently used during firework shows or at night while photographing bright cityscapes.

Aperture is:

Put simply, a hole that allows light to reach the recording medium. It can get larger or smaller in nearly all lenses.


Aperture controls:

First and foremost, the aperture’s main function is to control the amount of light entering the camera by increasing or decreasing the size of the hole.

Depth of Field:

Aperture is one way to control depth of field. The larger the aperture, the more shallow the depth of field will be. The smaller the aperture, the deeper the depth.

Camera Obscura

The Camera Obscura is simply a light tight box with a hole opposite of the recording medium. Occasionally, they may have a lens.

Aperture basics

In week one, we turned the entire room into a Camera Obscura, a primitive camera. The windows and doors were blackened with paper and a large hole was cut into the paper covering the window. 

This large hole was our aperture.

We used an old screen printing silk to project the image onto so that students could see how the image changed. Using pieces of paper with smaller and smaller holes, students could watch the resulting projected image become sharper yet more dark each time the hole diameter was decreased.

See the photos below for reference:


F-stops is the function of the lens’ focal length divided by the physical diameter of the aperture. For instance, a 500mm lens with a 50mm aperture diameter will be at f/10. A 200mm lens with a 50mm aperture diameter will be at f/4.

F-stops do not change between lenses. What I mean by that is if you have a 28mm lens at f/10 and a shutter speed of 1/60 and you change to a 300mm lens, your settings will not need to be changed (f/10, 1/60th). {note, this may not be exactly accurate because of light transmission properties or T-stops}.


Focal length/aperture diameter = f-stop number and are interchangeable between lenses

Depth of Field

Depth of Field (DoF) refers to how much of an image is in focus from near to far.

Depth of Field as it Relates to Apertures

A large aperture diameter (or lower f-stop number) will let in more light but the image will have a very narrow depth of field. Conversely, a small aperture diameter will create a deeper depth of field but will allow less light to reach the recording media.

For instance, if you are shooting a group of eight people, you will need a deeper depth of field to get them all in focus (a good rule of thumb for group numbers is f-stop = the number of people in the photo). If you are photographing a single person and want to isolate them from the background, a wide aperture will blur the background (bokeh) but keep the person in focus.