Aperture in Photography Explained

Aperture is arguably the most important camera setting that a photographer can learn. If you want to take photos with buttery smooth backgrounds, or landscapes that are sharp from front to back - you will need to learn to control aperture.
Updated: 11th June, 2020

    When moving from the ‘auto’ or ‘scene’ settings I always suggest that beginners start by putting their camera into ‘Aperture Priority’ mode and learning how aperture works and the effect it has on the ‘look’ of a photo.

    90% of the photos I capture are taken in aperture priority mode. 

    I use it in Landscape photography to make sure the scene is sharp from front to back, in portrait and wildlife photography to make the subject stand out from the background, in macro photography to make sure the tiny subject is properly focused…. You get the idea. 

    The only time I will switch to ‘Shutter Priority’ is when photographing very fast moving subjects that absolutely need very high shutter speeds to freeze the motion.

    Aperture is a simple topic, but one that can confuse new photographers. It may take you a little practice to grasp, but once you get the basics down it will skyrocket your ability to produce professional looking photos.

    So let’s get started

    What Is Aperture?

    In photography, aperture refers to the opening in a lens through which light passes before it hits the sensor.

    The bigger the opening in the lens, the more light can get through at once. 

    When taking a photo you can control the size of the opening, up to the maximum allowable by the lens you have. Opening the aperture to its maximum size is referred to as using the lens ‘wide open’. Using narrower apertures is known as ‘stopping down’ the lens.

    The photo below shows a Nikon 85mm lens set to its maximum aperture of f/1.8 (left) and stopped down to f/22 (right). You can clearly see the difference in the size of the hole that allows light through the lens.

    Front view of a Nikon 85mm lens showing it at maximum aperture and at f/22

    Aperture is represented by using f-numbers. Typically you will see them written as f/1.8, f/8, f/16 etc. Sometimes the forward slash is omitted f1.8, f8, f16, etc. Wider apertures are represented by smaller numbers (f/1.4, f/2.0, f/4), where as narrow apertures are written as larger numbers (f/16, f/22, f45).

    A lot of beginner photographers find the above statement confusing, but you will soon get the hang of it with some practice. Just remember: Wide Aperture = Small f-number, Narrow Aperture = Large f-number.

    What Happens In Aperture Priority Mode?

    When you turn your camera to Aperture Priority mode, you will choose the aperture and the camera will automatically calculate the appropriate Shutter Speed and ISO (if you have auto-iso enabled) to get the correct exposure.

    Sounds easy right? It really is.

    The Effect of Aperture On Photos

    Changing the aperture setting when taking a photo will have two main effects.

    Depth of Field

    The most dramatic effect of changing the aperture is how it affects the out of focus areas in front and behind the focus point in a photo.

    Large apertures mean that less of the background and foreground of your photo will be in focus. If you’ve ever seen a photo where the subject is perfectly sharp and the foreground and/or background is blurry, chances are that it was taken with a wide aperture setting.

    Conversely, photos where everything from the distant background, all the way to the foreground are sharp and in-focus (such as a landscape photo) will probably have been taken with a narrow aperture setting.

    How much of your photo is in focus is known as ‘Depth of Field’ Controlling the depth of field of your photos is one of the best ways you can turn a general snapshot into a ‘professional looking’ masterpiece.

    Let’s take a look at what that looks like in real life. In the image below you can see that at f/2.4 the focus is on the middle battery and the batteries in the fore and background are out of focus. This is what is known as a ‘shallow’ depth of field. Stopping the lens down to f/22 increases the depth of field so that the front and back batteries are brought into focus.

    Exposure

    Something you might not notice straight away if your camera is in Aperture Priority is the effect of changing aperture on your exposure.

    Now that you know that changing the aperture changes the amount of light coming into your lens, it makes sense that it will affect your exposure. If you change your aperture from f/4 to f/5.6 you halve the amount of light that comes into the lens. Your camera will compensate by doubling the shutter speed or ISO (or a combination of both).

    You can see the effect of changing aperture on exposure if you keep all other settings the same, adjusting just the aperture.

    Aperture Numbers. Clearing Up The Confusion

    One of the hardest concepts for beginner photographers to grasp is the relationship between the aperture number (f/1.4, f/2.8, f/8, f/16 etc) and the physical size of the aperture.

    You need to remember one thing: A wide aperture is represented by a small f-number. A narrow aperture is represented by a large f-number.

    The reason this is true that the f-number is actually a fraction. Let’s take the example of a 50mm lens. If you set the aperture to f/2.8: the ‘f’ in the aperture represents ‘focal length’. So in our example the aperture is 50mm / 1.4 = 35.7mm. That is, the hole in the lens that lets light through is 35.7mm in diameter. If we set the same lens to f/8.0 the equation becomes 50mm / 8 = 6.25mm - the hole becomes much smaller as the aperture narrows.

    How to Set Aperture on Your Camera

    To have control over the aperture setting you need to put your camera into either Aperture Priority mode or full manual mode.

    In Aperture Priority you will choose your desired aperture and the camera will choose the appropriate shutter speed for the correct exposure. If you have turned on auto-iso the camera will balance the shutter speed and ISO to get the correct exposure.

    How to set Aperture Priority on a Nikon D3300
    Aperture Priority Mode on a Nikon D3300

    The method to set Aperture Priority will vary depending on which camera you use. Generally you will set a mode dial to the Aperture Priority setting and then use a second dial or control wheel to change the aperture value. Consult your camera manual if you’re not sure on how to do this for your camera.

    How to Determine the Maximum Aperture of a Lens

    Each lens has a maximum aperture that can be set. A lens’ maximum aperture will usually be listed in the name of the lens. For example the ‘Nikkor 85mm f/1.8 AF-S G’ lens has a maximum aperture of f/1.8. Similarly, the ‘Canon EF 11-24mm f/4 L USM’ lens has a maximum aperture of f/4.

    Front of a Canon 50mm lens show the maximum aperture

    Lenses of the same focal length, but a larger maximum aperture will generally be larger, heavier and more expensive than those with smaller values. For example the Nikkor 50mm f/1.8 AF-S G lens weighs in at 185g and costs around US$180. The f/1.4 version of the lens is 280g and costs around US$380.

    Of course, each lens can be set to narrower apertures (eg f/8). The maximum aperture is just that, the widest that the lens can be set to.

    Fixed vs Variable Aperture Lenses

    You may have seen that some zoom lenses have more than one aperture listed in its name. For example, the ‘Sony FE 28-70mm f3.5-5.6 OSS’. This indicates that when zoomed out to 28mm the maximum aperture can be set to f/3.5, but when zoomed to 70mm the maximum aperture is f/5.6. When set to a focal length between 28 and 70mm the maximum aperture will be somewhere between 3.5 and 5.6.

    Markings on a Sigma 150-600mm lens showing the variable aperture

    Some Practice Exercises

    Learning photography is all about practicing for yourself and getting experience in different situations.

    In order to explore aperture, first put your camera into Aperture Priority Mode and enable Auto-ISO.

    Scenario 1:

    Find an area where you can have someone stand 15-20 metres in front of a background with some detail. A row of trees, a wall or a hedge. Use a lens of between 50 and 100mm and position yourself so you can frame the person’s head and shoulders to fill the photo, with some of the background showing at the edges of the frame. Make sure the camera is focusing on the person’s face.

    Set your aperture to the widest (lowest number) that your lens will allow and take a photo. Now change your aperture to something narrower (a higher number) and take the photo again. Repeat the process until you are at f/22 or so.

    When you take a look at the resulting photos you should see that the first photo you took has a much blurrier background than the last one, with each change in aperture showing more and more detail in the out of focus areas.

    Scenario 2:

    Find a landscape scene with objects/detail in the foreground, middle ground and background. A grassy field with a fence in the middle and some trees in the background. Or a scene with a walking path running from front to back. Keep the camera level, but move it close to the ground so that plenty of the foreground is present in the photo.

    Stop the camera down to f/22 and focus on something in the middle of the scene. Take the photo. Then open the lens to f/16 and take a second photo. Repeat the process, opening the aperture a little more each time you take the shot until you are at the widest setting for the lens.

    When you look through the photos you should see that the first photo has most or all of the photo in focus from front to back. As you move through subsequent photos you should see the foreground become less and less sharp. Depending on the scene you chose you may not see a difference until you get to the wider apertures.

    Recapping Some Definitions

    Hopefully you now know what aperture is and how it affects your photos. Below are some terms commonly used when talking about aperture

    • Aperture Priority: A camera mode that allows you to choose the aperture of a photo. The camera will automatically choose the appropriate shutter speed and/or ISO settings to get the correct exposure.
    • Aperture: The size of the opening in the lens that allows light to pass through before it hits the image sensor
    • F-Stop or F-Number: This is the number that represents the aperture size of the lens. f/1.4, f/2.0, f/11, f/22 are all examples of f-numbers. The number is a fraction based on the focal length of the lens and the diameter of the lens opening.
    • Wide Open: A lens is said to be ‘wide open’ when it is being used at its largest aperture setting (smallest f-number, see below)
    • Stop Down: To ‘stop down’ a lens means to use it at a narrower aperture (larger f-number) than its maximum.
    • Open Up: Opening up a lens is to move from a narrow aperture to a wider one.
    • Depth of Field: Refers to how much of the photo in front of and behind the focal point is in focus. A shallow depth of field indicates that a wide aperture was used and less of the foreground and background will be in focus.

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