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July 2, 2018

Photography 101: exposure, aperture, shutter speed, and ISO

by John_A



Every quality photo begins with exposure. Even if you catch a great subject at the perfect moment with strong framing, everything is lost if you blow the exposure. Photographers who shoot in automatic mode are accustomed to the camera taking care of all the settings. But, as smart as digital cameras have become, they aren’t perfect. Elevating your picture-taking from good to great requires a general understanding of the three elements of exposure: aperture, shutter speed, and ISO. Understand the interplay between these three elements, and you will be able to anticipate great photographs, rather than wait for happy coincidences.

The temptation to stick to auto mode is understandable: High-end digital cameras can be daunting, especially for anyone whose only prior camera was a smartphone. But once you know how a camera’s exposure settings work, a lot of that intimidation should be alleviated. When you have a basic understanding of aperture, shutter speed, and ISO – which are also the basics of photography, in general – you’re well on your way to mastering your digital camera’s advanced modes, even if you never opened the user manual. (Although, you really should read the manual too.)

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There’s a lot of technical mumbo-jumbo that goes into how a digital camera handles exposure, but we’ll attempt to keep this discussion in plain English as much as possible.

What is aperture?

The aperture is simply a hole within the lens that limits the amount of light that can pass through the lens. By changing the aperture value on your camera, you increase or decrease the size of that hole, thereby allowing more or less light into the camera. Aperture is measured in f-stops, such as f/22 and f/4, but here’s the thing: The smaller the f-stop number, the larger the opening, and vice versa. So, when you are adjusting the settings, think of the opposite: If you want less light to enter (small aperture), go for a larger f-stop. How large your lens’ aperture can open will depend on your lens. (Hint: A lens’ maximum aperture will be part of its model name, like a 50mm f/1.8 or a 12-120mm f/4.)

Beyond controlling the amount of light, aperture determines an image’s depth of field (DOF). Simply put, DOF is how depth will be in focus within the image. An image with a large DOF will have sharp focus from foreground to background, while a small (or “shallow”) DOF sees the focus concentrated on one particular focus plane, with foreground and background elements blurred away. When thinking about the f-stop, choose a smaller number (larger aperture to let in more light) to achieve a smaller DOF, or a larger number (smaller aperture, less light) to increase DOF.

A small aperture (larger f-number) helps keep both foreground and background elements in focus. (1/60 sec., f/16, ISO 400). Daven Mathies/Digital Trends
Daven Mathies/Digital Trends

When would you want to control aperture? The most common examples are portraits and landscapes. Portraits often look more appealing when the subject is separated from the background, which a DOF will achieve. On the other hand, for landscapes we typically want everything to be in sharp focus, from the foliage in the foreground the distant mountains. If you’re not sure how much depth of field you need, the beauty of digital photography is the ability to “guess and check.” Simply take a photo, check it out on the camera’s LCD screen, and either increase or decrease the size of the aperture to get the desired DOF.

A large aperture (small f-number) is commonly used in portraits to separate the subject from background and foreground elements. (1/125 sec., f/1.6, ISO 200). Daven Mathies/Digital Trends
Daven Mathies/Digital Trends

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