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Use the Aperture to Control the Background in a Photo

Your camera's aperture setting gives you creative control over the look and feel of your photos--learn how to use it properly.

Are you a manual transmission or an automatic transmission kind of person? If you enjoy shifting gears rather than letting the car do it for you, you probably also appreciate taking control of other gadgets, like your camera. But even if you drive your car by moving the stick from P to D, I am sure you'll enjoy mastering your camera's various exposure controls--it just makes for better photography. Recently, I explained how you can improve your photos by understanding when and how to change the shutter speed. That's only half the story, though. This week, let's see how your camera's aperture control can give you a range of different effects.

What Is Aperture and F-Stop?

It helps to understand what, exactly, the aperture is--and what it does. Simply put, your camera's aperture varies the size of the opening in the lens that exposes the sensor to light. A larger opening lets in more light, while a smaller aperture admits less light. Consequently, this setting is usually paired with the shutter speed. To take a properly exposed photo, you can use a small aperture with a slow shutter speed, or a larger aperture with a relatively faster shutter speed.

The size of the aperture is measured using something called an f-stop, or an f-number. You've probably seen these numbers on the barrel of a lens or in the display of your camera: f/4, f/5.6, f/8, and so on. Here's where photography gets a little mathy. The f-number is the ratio of the lens's focal length to the size of the aperture. That's nice to know, but all you really need to remember is that the size of the f-number and the actual size of the aperture opening are opposites: A large f-number (like f/22) is a small opening, while a small f-number (like f/4) is a large opening.

An Artistically Blurry Background

Now that you know those basics, I've got one more fact for you, and then you're ready to apply it to some real-world photographic situations.

You probably know that depth of field is the region of a photo that is acceptably sharp. A narrow depth of field is useful for situations in which you only want the subject in focus and the background to appear blurry. People portraits are just this sort of occasion--a sharply defined background can be distracting. You'll want to make the depth of field as narrow as possible so details blur away, leaving only the subject in sharp focus.

The larger the aperture (the smaller the f-number) the narrower the depth of field. So if you're shooting a portrait, for example, put your camera in Aperture Priority mode and then dial in the smallest f-number available.

Remember that a small f-number corresponds to a large aperture opening, so you're letting in a lot of light, and the shutter speed will be relatively short. This is a great all-around mode to use for sharp photos that don't suffer from camera shake, even in comparatively low light.

A Nice Sharp Photo

Sometimes you want just the opposite--you'd like as much of the photo to be in sharp focus as possible. Imagine you're taking a group photo, for example, with several rows of people in the shot. Or you're taking a photo of someone and it's important to capture the overall scene, so you don't want the background to blur away.

In this situation, you can rely on the opposite aperture setting because a large f-number delivers a large depth of field. So again, set your camera to Aperture Priority. But this time, dial it as high as it will go, like f/11 or f/22.

Keep in mind that this is going to result in a very small lens opening, so the shutter speed will have to be much longer to properly expose the photo. You might find the shutter speed is too long to hold it steady. Shoot these kinds of photos in the best light available, or increase the ISO. That will make the sensor more sensitive to light, and allow you to shoot at a higher shutter speed.

The ultimate in front-to-back sharpness comes from a technique called hyperfocal photography, in which you set the aperture so that everything from the nearest subject to infinity is relatively sharp. You can read more about how to do this in "Maximize Your Depth of Field With Hyperfocal Photography."

Look for a Fast Lens

If you have a digital SLR, you might consider buying a faster lens to give you more flexibility when shooting in aperture priority. When photographers talk about a fast lens, they are talking about the maximum aperture (smallest f-number) the lens is capable of. While most average lenses can go no higher than f/5.6 or perhaps f/4, you can find premium lenses that can open up to f/2 or even better. Yes, they cost more--but they allow you to shoot in much dimmer light, and their huge aperture can generate some wonderfully narrow depth of field.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality, and technique.

Great news! For a limited time (from March 1 till August 31, 2012), Hot Pic of the Week winners will receive one free downloadable copy of Corel PaintShop Pro X4.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 800 by 600 pixels. Entries at higher resolutions will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo along with a short description and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering, please read the full description of the contest rules and regulations.

This week's Hot Pic: "First Snow" by Kathryn Lake Clue, Chicago, Illinois

Kathryn writes: "I have a Canon EOS 30D with an amazing new lens, the Sigma 50mm 1:1.4, which I've found allows for fantastic portraits with beautiful background blur--like I captured in this shot."

This week's runner-up: "The Bird" by Ronald Knapik, Amsterdam, New York

Ronald took this photo with a Canon EOS 10D on the beach in Longboat Key, Florida.

To see winners for May, visit last month's Hot Pics slide show. Visit the Hot Pics Flickr gallery to browse past winners.

Have a digital photo question? E-mail me your comments, questions, and suggestions about the newsletter itself. And be sure to sign up to have Digital Focus e-mailed to you each week.

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