It Starts with a Blurry Background or a Dark Room
You picked up your Canon camera because you wanted to capture the world more beautifully. You saw a stunning portrait online with that dreamy, soft blur behind the subject, or a crisp landscape where every leaf was sharp. You tried to recreate it, but no matter which dial you turned, your photo didn’t look right. The background was distractingly busy, or your entire shot was too dark.
The secret ingredient you were missing is almost certainly the aperture setting. It’s one of the three pillars of photography, alongside shutter speed and ISO. Mastering it is the difference between taking a snapshot and making a photograph. Changing the aperture on your Canon camera gives you direct creative control over the look and feel of your image.
This guide will walk you through exactly how to find and change the aperture on any modern Canon DSLR or mirrorless camera. We’ll move from the simple basics to the nuanced creative choices, so you can confidently make the changes that lead to the photos you envision.
Understanding What Aperture Actually Does
Before we touch any dials, it helps to know what you’re controlling. Think of the aperture as the pupil of your camera’s lens. It’s an iris of metal blades that can open wide or close down to a tiny hole.
This opening controls two fundamental things: the amount of light that hits the camera sensor, and the depth of field. Depth of field is simply the zone of acceptable sharpness in front of and behind your point of focus.
A wide aperture, represented by a low f-number like f/1.8 or f/2.8, lets in a lot of light and creates a very shallow depth of field. This is perfect for isolating a subject with a beautifully blurred background or foreground, often called “bokeh.”
A narrow aperture, represented by a high f-number like f/11 or f/16, lets in less light and creates a deep depth of field. This keeps everything from the foreground to the distant horizon in sharp focus, which is essential for landscapes and architecture.
The First Step: Getting into the Right Shooting Mode
You cannot change the aperture in full Auto mode. Your camera needs you to take partial control. The two main modes for controlling aperture on a Canon are Aperture Priority (Av) and Manual (M) mode.
Locate the mode dial on the top of your camera. It’s usually a round dial with icons like a green rectangle (Full Auto), P, Tv, Av, and M. For learning aperture, Aperture Priority (Av) is your best friend.
Why Aperture Priority Mode is Your Gateway
Turn the dial to Av. In this mode, you set the aperture, and the camera automatically selects the appropriate shutter speed to get a properly exposed photo. This lets you focus purely on the creative effect of depth of field without worrying about the image being too dark or too bright.
It’s the perfect balance of control and assistance. Once you’re comfortable in Av, you can graduate to Manual (M) mode, where you control both aperture and shutter speed independently.
How to Physically Change the Aperture Setting
The control method varies slightly between Canon DSLRs (like the Rebel, 90D, or 5D series) and newer mirrorless cameras (like the EOS R series), but the principle is the same.
For Canon DSLR Cameras
With your camera in Av or M mode, look at the top LCD screen or the viewfinder display. You will see the current f-number.
To change it, use the main dial. This is the large, ribbed wheel located just behind the shutter button, typically operated with your right index finger. Rotating this dial left or right will change the f-number.
Rotating the dial to the right (clockwise) will usually make the f-number larger (e.g., f/5.6 to f/8), which is a smaller aperture. Rotating it to the left (counter-clockwise) will make the f-number smaller (e.g., f/5.6 to f/4), which is a wider aperture.
For Canon EOS R Series Mirrorless Cameras
The process is very similar. In Av or M mode, the f-number is displayed on the rear screen or in the electronic viewfinder.
The main control dial behind the shutter button works identically. However, many R series cameras also have a second control ring on the lens itself. By default, this lens control ring can be programmed to adjust aperture. Check your camera’s custom functions menu if you want to change this assignment.
The most direct method is simply using the main dial behind the shutter button, just like on a DSLR.
Seeing the Change in Real Time
One of the great advantages of digital cameras and electronic viewfinders is that you can see the effect before you press the shutter. As you change the aperture, watch the scene in your viewfinder or on the live view screen.
When you select a wide aperture (low f-number), you’ll see the background become more blurred. When you select a narrow aperture (high f-number), you’ll see more of the scene come into focus.
Note: On most DSLRs using the optical viewfinder, you won’t see this depth-of-field change until you take the photo, because the lens stays at its widest aperture for a bright viewfinder. Press the “Depth of Field Preview” button, usually located near the lens mount, to stop the lens down to your selected aperture and see the actual effect.
Choosing the Right Aperture for Your Scene
Now that you know the mechanics, here’s how to apply it. These are practical starting points for common situations.
Portraits and Subject Isolation
Use a wide aperture. Start between f/1.8 and f/4, depending on your lens. This throws the background into a soft blur, making your subject pop. Be mindful of focus, as the shallow depth of field means eyes must be perfectly sharp.
Landscape and Architecture Photography
Use a narrow aperture. Settings from f/8 to f/16 will keep everything from nearby rocks to distant mountains in focus. Be aware that using the very narrowest apertures (like f/22) can sometimes reduce overall sharpness due to an optical effect called diffraction.
Group Photos
You need enough depth of field to get everyone’s face sharp. Move to f/5.6 or f/8. Make sure everyone is roughly in the same plane (not standing in a deep line) for best results.
Everyday and Street Photography
A versatile “walk-around” aperture is f/5.6 to f/8. It gives you a good balance of light, depth of field, and sharpness for spontaneous shots.
Low Light and Night Photography
You need to gather as much light as possible. Open up to your lens’s widest aperture (e.g., f/1.8, f/2.8). This lets you use a faster shutter speed to avoid blur and a lower ISO to reduce grain.
Troubleshooting Common Aperture Issues
Even when you know the steps, things can go wrong. Here’s how to diagnose and fix common problems.
The Aperture Won’t Change or is Grayed Out
First, double-check you are in Av or M mode. If you are, the lens might not be communicating properly. Remove and re-seat the lens, ensuring it clicks into place. If the problem persists with a specific lens, there may be an internal mechanical issue.
The Shutter Speed is Blinking in the Viewfinder
In Av mode, a blinking shutter speed means the camera cannot find a correct exposure for your chosen aperture. If the shutter speed blinks at a high number like “8000,” your aperture is too wide for the bright light, overexposing the image. Close down the aperture (use a higher f-number). If it blinks at a low number like “30”,” your aperture is too narrow for the dark scene, risking underexposure. Open up the aperture (use a lower f-number) or increase your ISO.
Photos are Too Dark or Too Bright in Aperture Priority
Remember, Av mode only controls depth of field. If your photos are consistently under or overexposed, use Exposure Compensation. Press the +/- button and turn the main dial to adjust the overall brightness up or down. The camera will stick to your chosen aperture but adjust its shutter speed to make the image brighter or darker.
Moving Beyond the Basics: Lens Limits and Sweet Spots
Every lens has a maximum aperture, listed on the lens barrel (e.g., “Canon 50mm f/1.8”). This is the widest it can open. Most zoom lenses have a variable maximum, like “f/3.5-5.6,” meaning it’s f/3.5 at the wide end and f/5.6 at the telephoto end.
Conversely, nearly every lens has an “aperture sweet spot,” usually 2-3 stops down from its maximum aperture. For an f/1.8 lens, that’s around f/4. At this setting, the lens often achieves its peak optical sharpness across the frame.
Don’t be afraid to use your lens at its maximum aperture for creative effect, but for critical sharpness, especially in landscapes, stopping down to the sweet spot is a professional trick.
Your Creative Control is Now in Your Hands
Changing the aperture on your Canon camera is the technical key to unlocking creative expression. It transforms your camera from a recording device into a tool for artistic choice. You decide what is emphasized and what recedes into the background.
The best way to learn is by doing. Set your camera to Av mode today and spend an hour taking the same photo of a subject at every aperture your lens allows. Watch how the relationship between subject and background changes with each click of the dial.
Soon, selecting the right f-number will become second nature—a fundamental part of how you see and shape the light. Start with controlling the blur, and you’ve taken the single most important step toward mastering your camera.
