Canon EOS 90D For Dummies
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The aperture is the opening in the lens that lets light into the digital camera. The size of aperture you choose determines how much of your image is in sharp focus from front to back, which is known as depth of field.

The aperture in your camera lens is adjustable. The size of the aperture is referred to as the f-stop. A large f-stop number designates a small aperture, and a small f-stop number designates a large aperture. The range of available f-stops varies depending on the lens you have, and whether the lens is a telephoto lens.

For example, a Canon EF 50mm f/1.4 has an aperture range from f/1.4 to f/22. A lens with an f-stop value of f/2.8 (large aperture) or lower is considered a fast lens because you can open the aperture (choose a low f-stop value) to let a lot of light into the camera. Lenses shed light on your sensor.

A small f-stop value (large aperture) gives you a shallow depth of field, and a large f-stop value (small aperture) gives you a large depth of field. The depth of field gradually increases as you choose a smaller aperture (larger f-stop value), which is also known as closing down the aperture.

The easiest way to learn what a specific lens will do at a given f-stop value is to experiment with the lens while shooting in Aperture Priority mode. Take a picture of the same subject from the same distance with different f-stop values. When you examine the images on your computer, you’ll grasp the relationship of f-stop and depth of field.

Depth of field plays a vital role in nature photography. Some subjects warrant a large depth of field, and other subjects beg for a shallow depth of field. When you photograph a wonderful landscape that seems to go on forever, such as the beautiful vista from Tunnel View in Yosemite Valley, you need a large depth of field and an f-stop of f/11 or larger.


When you photograph an animal or a flower, choose a relatively shallow depth of field to draw your viewer’s attention to your subject. The focal length you choose is also a factor.


About This Article

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About the book authors:

Robert Correll has more than two decades of experience in writing and photography. He is the author of all previous editions of Digital SLR Photography All-in-One For Dummies and has written several other books specific to individual DSLR camera models. Julie Adair King is a veteran photography professional and instructor with more than 60 books to her credit. She has written all editions of Digital Photography For Dummies as well as 40 guides to DSLR camera models.

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