DSLR Photography 101: What is Aperture?

Megan O'Neill


If you’ve recently jumped on the DSLR bandwagon, you know that all the manual settings can be overwhelming, especially if you don’t have any experience with photography. That’s why we’ve launched a DSLR Photography 101 series, to help you up your photo game and move from automatic to manual. Over the past few weeks, we’ve explained ISO and shutter speed. Today we’re taking a look at aperture.

Aperture is defined as the opening, or hole, in a photographic lens that allows light to reach the sensor in your camera. It’s measured in f-stops. The lower the f-stop number, the larger the opening. The larger the f-stop number, the smaller the opening. This can be confusing, but the following diagram should help. F-stop settings are listed along the bottom.

Camera Aperture Diagram

Aperture not only controls the amount of light reaching the sensor, but it also affects the depth of field in your photograph. Depth of field is defined as the distance between the nearest and furthest objects in a photo that appear in focus. A smaller aperture (larger f-stop number) results in an image with a wider depth of field. A larger aperture (smaller f-stop number) results in an image with a shallow depth of field.

In the images below, you can see how aperture affects the depth of field in your photographs. These images were all photographed with the subject 3 feet in front of the backdrop using various apertures. See how the background in the image on the left, with the largest aperture (smallest f-stop number), appears blurry in the background and foreground, while the subject’s face appears in focus? That’s what shallow depth of field looks like. Compare it to the crisp image on the right with the smallest aperture (largest f-stop number). That’s what wide depth of field looks like.

aperture example

Deciding which f-stop to use

How do you decide which f-stop to use? Well, if you’d like to blur out the background with a shallow depth of field then you’d want to use a smaller numbered f-stop (i.e. 1.4, 2, 2.8, 4). If you want your entire photo to be in focus, use a larger numbered f-stop (i.e. 16, 22). Use the middle numbered f-stops to get different levels of focus along the spectrum.

Our Consumer Customer Owner Beth recommends using smaller apertures (larger f-stops) for landscape photography to retain more sharpness from the foreground to the horizon. She recommends lower apertures (smaller f-stops) for portrait photography. This results in a blurry background, which draws the viewer’s attention to the subject (as in the example on the left above).

Aperture, shutter speed, and ISO

Because we’ve taken a look at shutter speed, ISO, and aperture over the past few weeks, we thought we’d come full circle and explain how they all work together.

Exposure is controlled by all three of these elements, which are often referred to as the exposure triangle. When you use your camera in automatic mode, the camera assesses the scene and adjusts each of these elements in order to expose the image the best that it can under the given circumstances.

Most cameras these days do a pretty good job of getting the exposure correct on the automatic setting. However, if you want more control over the final look of your image, you’ll need to take control of these elements yourself and switch to manual mode. In manual mode, you’ll have to play around to find a balance between the three elements — ISO, shutter speed, and aperture — that works for your needs.

As an example, let’s say you’re at a sporting event. You’ll probably want to use a shutter speed of around 1/1000 in order to stop the action of your subject. However, because the shutter will only be open for a very short time (1/1000th of a second), you may need to increase your camera sensor’s sensitivity to light to get the best shot. You can do this by increasing your ISO or using a lower aperture (wider hole) to allow more light to pass through the lens.

Remember, when you’re shooting on a DSLR you’ve got the benefit of being able to look at your photos right away, so, if you don’t like the effect of a certain setting, you can always change it up on the spot.

Stay tuned for more of our DSLR Photography 101 series next Friday, where we’ll be discussing different types of lenses and what each is best for.

Using a DSLR camera? We’d love to see your shots. Share them with us in the comments below.

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