Digital Focus: Choose the Right Exposure Mode

All about exposure, aperture, shutter priority, and flash memory.

Dave Johnson

Feature: Choosing the Right Exposure Mode

Which is more neglected: the Maytag repairman or those exposure mode controls on your digital camera? At least the Maytag guy can complain to people on TV occasionally. For many folks, the exposure controls never even get a second thought.

If you leave your camera on its full-automatic setting all the time, this week's newsletter is for you. You'll get no argument from me that your camera's Auto setting is great... at least half the time. There are many occasions, though, when a few tweaks could save the day, or at least give you a better picture.

Aperture Takes Priority

Many digital cameras come with a pair of exposure modes called Aperture Priority and Shutter Priority. These are great when you want to get a little creative.

Aperture Priority, often abbreviated with just the letter A on the camera's LCD menu or on a dial on top of the camera, is the mode to choose when you want direct control over how much of the image is in sharp focus, but you still want the camera to work in a mostly automated way. This control lets you dial in the aperture setting for your picture, and the camera itself calculates and sets the appropriate shutter speed to match.

When you set a big aperture value, like f/11 or f/16, you're maximizing the depth of field in the picture. The entire depth of the image, from the front to the back, will be in sharp focus. On the other hand, you can set a low f/stop, like f/2 or f/4, to minimize the depth of field. Only the subject will be in sharp focus, and the background will be comfortably blurred.

Why would you care about this? Depth of field mostly becomes an issue when shooting portraits, because the subject will stand out from the background better if it is the only thing in focus. The Aperture Priority setting can come in handy at other times, too. If you're taking a close-up photo, such as a shot of a bug on a leaf, you'll want to maximize your depth of field. Depth of field gets really shallow in macro-photography, so when you're engaged in taking pictures of small subjects like bugs, coins, jewelry, and flowers, you want to dial-in as much as you possibly can to keep your entire subject in sharp focus.

When Speed Counts

Shutter Priority (often abbreviated with an S) lets you change the other exposure variable. Using Shutter Priority, you can select any shutter speed from very fast to quite slow. Select a shutter speed, and the camera adjusts the aperture to match. Note that digital cameras tend to have maximum shutter speeds of up to 1/500 or 1/1000 of a second, and they can handle shutter speeds as low as 1, 2, or even 8 seconds--as long as the camera thinks the lighting is low enough to allow such long exposures.

The Shutter Priority mode is usually most helpful in motion photography. Want to freeze the action? Pick a very fast shutter speed; the faster the better. Want to show "motion blur" in action shots? Slow down the shutter speed.

Of course, you're astute enough to realize that since your camera's shutter speed and aperture setting are so closely related, both controls really do the same thing. So if your camera doesn't have an Aperture Priority control but it does have Shutter Priority, you can set the shutter speed high in order to reduce the depth of field and get a blurry background. If you have both controls, though, use whichever one gives you the most direct control over your subject. After all, these program modes are there for your convenience.

Taking Manual Control

If your camera has a manual exposure control, you'll probably never use it--and I wouldn't blame you. The automatic and priority modes are fine 99 percent of the time. In fact, there are very few situations in which manual control would come in handy.

The most common situation in which I switch to manual control is night photography. Auto-exposure controls aren't particularly useful at night; I often end up switching to manual and taking a long time-exposure with the aperture wide open. I'll give you details on how to do that in a future newsletter.

Dave's Favorites: Crop and Resize With A Smaller Image 3.0

Ever since little girls started posing with fake fairies back in 1917, photos have been meant for sharing. These notorious images were some of the earliest examples of trick photography, and were even championed by an all-too-gullible Sir Arthur Conan Doyle.

But for sharing pictures via e-mail, 3-megapixel digital images are cumbersome. I've often suggested that you resize pictures in your favorite image editor before attaching them to electronic messages. A better alternative might be a program called A Smaller Image, from TriVista.

This simple $15 program is designed from the ground up to crop and resize photos. Just drag an image into the application window and move a cropping frame around the screen until you've got you want. The cool part is that you can configure the cropping frame's proportion based on how large you want the resulting photo to be, so there's absolutely no guesswork. Set the end photo size to 640 by 480, for instance, and the cropping frame is proportioned correctly for the job. You can also scale the cropping frame to include more or less of the original image in the new, re-sized photo. It's all very clever and makes you wonder why no one thought of that before.

A Smaller Image also includes sharpness, brightness, and contrast controls, an optional graphic border for images, and a simple text tool for adding captions. If you frequently re-size photos for e-mail, the Web, or printing, A Smaller Image is an essential tool. For $15, you can't go wrong.

Q&A: Do Memory Cards Deteriorate?

I was recently told by a salesperson that CompactFlash memory cards will deteriorate after about one year of use. In other words, the quality of the images recorded on them will deteriorate with time. Is that true, or is the salesperson not telling the truth?

--C.C. Chu, Cornell University

Digital photography is a high-tech blend of traditional photography and computers, so it's not surprising that it is hard to be a good salesperson in this biz. You have to know a lot about many different topics, and you have to stay on top of technology that changes almost every day. Now that I've tried to soften the blow for that poor salesperson, let me say that that's the silliest load of malarkey I've ever heard!

Flash memory--like CompactFlash, SmartMedia, and Memory Stick--doesn't deteriorate over time in a way that affects the quality of the images stored on it. That's a very "analog" way to look at the world. Videotapes deteriorate, for instance, just by being played or even by sitting quietly on a shelf, and the image quality suffers as a consequence. Digital media, though, doesn't work that way.

Memory cards will function just fine for years and years if properly cared for. However, a number of factors can damage them and render their data unreadable. Exposure to temperature extremes can damage the cards (though testing has shown them to be unbelievably resilient), as can removing them while data is actually being recorded. And if you like to use them to send pictures to grandma via snail mail, think again: The CompactFlash Association warned in January that the irradiation used to sanitize U.S. mail can cause CF media to become both unreadable and unusable. Another casualty of the anthrax scare!

But if you take care of your cards, they'll last and last. I wouldn't worry about your memory cards wearing out anytime soon.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality, and technique. Every month, the best of the weekly winners gets a prize valued at between $10 and $100.

A gentle reminder, folks: We disqualify some really wonderful pictures every week because the submissions don't follow the rules. Be sure to include everything we ask for in your e-mail message, including a description of your picture and your complete contact information, or your entry is wasted!

Here's how to enter: Send us your photograph in JPEG format at a resolution no higher than 640 by 480 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 regs.

This week's Hot Pic: "Pelican Sunrise," by Brian Olson, Vernon, British Columbia

Brian says that he took this photo back in January, during a "feeding frenzy" at sunrise. He used a Kodak DC 3200 to capture the scene in Santiago Bay."

We want your feedback! Send your comments, questions, and suggestions about the newsletter itself to comments@bydavejohnson.com. If you have a question that you'd like to see answered in the weekly Q&A, send it to question@bydavejohnson.com.

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