The Exposure Triangle: How Shutter Speed, Aperture, and ISO Work Together in Photography

The exposure triangle (or exposure value) in photography is a principle that determines the amount of light that reaches your camera sensor. The exposure triangle has three parts:

• Shutter Speed
• Aperture
• ISO

Whether with film or digital photography, in order to achieve a properly exposed photo, you need to make sure that all three elements are working in harmony. That means that if one element changes, the other two need to change as well.

Also known as exposure time, this is how long the camera shutter is open and the digital sensor or film is exposed to light. Shutter speed is expressed as a unit of time: 1/100 means that your shutter was open for 1/100th of a second. Shutter speed allows you to freeze or blur a subject in motion.

This is how big the opening is that lets light into your camera. Your aperture is determined by your camera lens, and is measured in F-stops. The larger the f-stop number, the smaller the opening is, and therefore, the less light it lets into the camera. For example, f2.8 allows twice as much light into the camera as f4, and 16 times as much light as f11. In addition to the brightness of your photos, aperture affects the depth of field: larger openings create a shallower depth of field, while smaller openings bring more of the image into focus.

This is how sensitive your camera’s sensor is to light, expressed as a number (e.g. ISO 100, ISO 200, etc.) ISO stands for the International Organization of Standardization, which establishes sensitivity ratings for camera sensors. The higher the ISO value, the more sensitive you camera will be to light, making high ISO values useful for night photography. However, increasing ISO can also increase digital noise in your images, so you typically want your native ISO setting to be as low as possible for your camera.

When it comes to ISO, note that a film camera will have different numbers than on a DSLR or mirrorless camera. With a film camera, ISO is represented by numbers ranging from 100 to 6400. The higher the ISO in a film camera, the more sensitive the film is to light. With a digital camera, ISO relates to the sensitivity of the image sensor. The higher the ISO, the more sensitive the camera is to light. If you’re capturing motion blur when there’s a lot of light, using a lower ISO with a longer shutter speed will help prevent overexposure.

All three of these camera settings work in conjunction with one another to achieve the correct exposure for your images. For example, if you open up the aperture to let in more light, you will need to use either a fast shutter speed, or a low ISO to compensate.

Your camera is the most powerful tool in helping you gain proper exposure. It has various modes which allow customizable controls over the three parts of the exposure triangle.

These are the three main camera modes:

Manual Mode
You set a specific shutter speed, aperture, and ISO. This is useful if you want complete control of your camera settings, and you have time to adjust them for each shot.

Shutter Priority Mode
You set a specific shutter speed and the camera automatically selects the aperture. This is useful when your subject is on the move.

Aperture Priority Mode
You set a specific aperture, and the camera automatically selects the shutter speed. This is useful when you want to control the depth of field.

Both Aperture Priority and Shutter Priority have their uses, and you’ll often find yourself switching back and forth, depending on what you’re shooting. It often makes sense to set your ISO to Auto when you’re shooting in these modes, so that the camera has more flexibility to make decisions to get the shot right.

The exposure triangle can be manipulated to create different effects in your photos. Here are some ways that you can play with these settings:

1. Motion blur:
The key to creating motion blur in your photos is shutter speed. The longer your shutter speed, the more blur and motion you’ll be able to capture. If you’re using the Shutter Priority Mode on your camera, yout aperture and ISO will change automatically to match your change in shutter speed. If you’re using manual mode, be sure to adjust both as well. Both shutter speed and aperture are set up in “stops.” A decrease of one stop in shutter speed is equal to double the length of time the shutter is open. Meanwhile, a decrease in aperture of one stop is equal to a 50 percent decrease in the size of the shutter opening. The numbers are proportional, so each stop on one setting aligns with a stop on the other.

2. Frozen Motion:
If you’re looking to freeze the action in a photo—picture droplets of water suspended in the air as a dolphin dives into the ocean—you’ll want to increase shutter speed. The higher the speed of the object you’re trying to capture, the higher your shutter speed should be. Try starting at 1/500 and going from there. Adjust ISO and aperture as you increase your shutter speed. Both aperture and ISO should go up proportionately as shutter speed goes up. If you’re using Shutter Priority Mode, this will be done automatically, but if you’re doing it manually, you’ll have to adjust it yourself.

3. Night shots:
With night photography, it’s a good idea to work in manual mode and utilize a good tripod. Your aperture needs to be lower than it would be on a sunny day, ISO should be as low as possible, and shutter speed can be long if you’re looking for blur or shorter if you want a crisper image.

4. Depth of Field:
Controlling the amount of the photo that is in focus is one of the photographer’s best tools for drawing the viewer’s eye where you want it. For example, landscape photography is typically shot so that everything is in focus. To achieve this, photographers will shoot at small apertures (e.g. f11 or f16), resulting in a larger depth of field. On the other end of the spectrum, a large aperture results in a shallow depth of field, limiting focus to a small part of your subject. Bokeh is one popular photography method that utilizes a shallow depth of field. When shooting bokeh, set your lens to the lowest aperture and adjust ISO and shutter speed accordingly, or use Shutter Priority Mode. Note that focal length also contributes to depth of field, with a longer focal length corresponding to a shallower depth of field.

Use the following guide to get the right exposure and effect every time you snap a photo:

Shutter speed: How long the shutter is open, expressed as a measurement of time. 1/100 = 1/100th of a second.

Aperture: How big the opening is that lets light in, expressed in F-stops. The larger the number, the smaller the opening.

ISO: How sensitive your camera’s sensor is to light. The higher the ISO number, the more sensitive to light.

Motion blur: Longer shutter speed, lower aperture, lower ISO

Frozen motion: Higher shutter speed, higher aperture, higher ISO.

Night shots: In low light scenarios, manual mode, lower aperture, lowest ISO, shutter speed varies based on type of image.

Depth of field: Larger aperture and longer focal length corresponds with shallower depth of field. Small aperture and shorter focal length corresponds with larger depth of field.

Regardless of the subject matter you wish to shoot, understanding exposure is crucial to ensuring that the image you want and the image you end up with are one and the same.

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