So What is Aperture Anyway?

So you’re just starting out in photography, or maybe you are trying to take your photography skills to the next level. You keep hearing this term, aperture, over and over again. What does it mean? How does it relate to photography? Well, aperture might sound like a complicated word, but it’s most likely much easier than you think. The literal definition: Aperture – a space through which light passes in an optical or photographic instrument, especially the variable opening by which light enters a camera. So what does this mean in preschool terms? Aperture is the amount of light passing through your camera lens to the camera sensor. It’s that simple.

Wide Aperture vs. Narrow Aperture

Measuring aperture can become a bit confusing. Mainly because on the numbered scale that measures aperture, the smaller the number the larger (or wider) the aperture. Remember, aperture is simply the amount of light passing through your camera lens to the camera sensor, so that means the smaller the number the more light hitting your camera sensor.

How is Aperture Measured?

Aperture is measured on a numbered scale of different light stops, or f-stops. F-stop (sometimes called f-number or f-ratio) stands for focal ratio. If you look at any of your lenses, there will most likely be your lens brand, focal length, and then f with a number beside it. This number represents the widest aperture your lens can open to. For example, if your lens says Canon 18-50 f3.5-5.6 this means you have a Canon lens that can cover the focal range of 18-50 millimeters. The widest aperture the lens can achieve at 18mm is 3.5, and the widest it can achieve at 50mm is 5.6. This simply means that the lens can let in more light at 18mm than at 50mm. (Remember the smaller number more light thing?) If there is only one number after f this means your lens has a constant aperture across all focal lengths. Zoom lenses that have constant aperture are almost always more expensive, and are usually premium lenses. Prime lenses will always only have one f-number. Prime lenses are also more likely to have wider maximum apertures than zoom lenses. Remember, the smaller the number, the larger the aperture. Usually, the smaller the f-number on the lens, the more expensive the lens will be, because that lens can let in more light.

F-Stop Scale

The aperture scale goes as follows: 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 – 45. Each increasing number is approximately itself multiplied by 1.4. However, if you try to adjust the aperture on your camera while you have a lens mounted, you most likely will not be able to go to 1, and you will also be able to select a lot of different numbers between the numbers I listed on the scale. This is because the camera will only let you go down to whatever your lens’ maximum aperture is (so if you have a f4 lens, 4 will be your maximum aperture). Also, you can select more numbers than are on the scale because each number on the scale represents a full stop of light, while the camera most likely lets you adjust your aperture in either half stops or 1/3 stops.

Aperture and Depth of Field

Adjusting your aperture is not only useful for letting more light hit your sensor, but it also can change the depth of field in an image. A wider (larger) aperture will give you a more shallow depth of field (part of the image that is in focus), while a more narrow (smaller) aperture will give you a depth of field that is deeper. When you see a photo with a blurred, creamy background this was most likely created using a wide aperture. This technique is frequently used in portrait photography.

Example of depth of field at f2.8.

Example of depth of field at f2.8. The background, and even parts of the couples’ faces are out of focus because of the narrow depth of field.

When you see a photo where the whole image is in focus, the photographer used a narrow aperture. This technique is frequently used in landscape and street photography.

Example of depth of field at f11. Notice how everything in the frame is in focus.

Example of depth of field at f11. Notice how everything in the frame is in focus.

An easy way to remember it is: A wide aperture creates a narrow depth of field, and a narrow aperture creates a wide depth of field. An exercise you can try is to take two similar objects and space them about 10 inches apart on a counter. Then place your camera in Aperture Priority mode (look below) about 1 foot from the closest object. Use your widest aperture lens, set it to it’s widest aperture, and focus on the object closest to your camera. Take a picture. Then, move up one full f-stop (check the chart above to find the f-stops). Take another picture. Do this all the way up to f8 or f11. Then compare the pictures to see the difference in depth of field. See how the out of focus object comes into focus the more narrow your aperture is? I did this exercise using wine corks and a 50mm f1.4 lens. Click any of the pictures to see a larger version.

Aperture Priority Mode

Most DSLR cameras have an “aperture priority” mode on them. On Canon, this is Av mode.

Photo of Canon 5D Mark III on Aperture Priority Mode On Nikon this is simply called A. If you switch to this mode, you will take control of your aperture setting and your camera will adjust all other settings to maintain a proper exposure. This is a great way to get off the ground when first learning manual exposure. Play around with your aperture on your camera, both for amount of light you let in the sensor and also to adjust the depth of field.

I hope you found this article helpful. If you did please leave a comment then share it so that others just like you can learn from it. Make sure to always keep practicing, and check out the next post where we will be discussing shutter speed.






About the Author: Jared Jarvis is a professional photographer based out of Houston, TX. He is the owner and lead photographer at Jared Jarvis Photography. He specializes in event, engagement, and wedding photography. To view his work, or contact him, click here.