Digital Focus: Accessory Lenses, CompactFlash Cards

Using Accessory Lenses

Last year, wandering around the Grand Tetons of Wyoming, I accidentally blundered into one of the most exciting photographic opportunities I'd ever experienced: A coyote was actively hunting down a rabbit right before my very eyes. As you can well imagine, I set up my camera and started snapping photos.

It was a once in a lifetime experience, to be sure. But unfortunately, the photos were underwhelming. In fact, I didn't consider a single shot from that sequence to be a "keeper." Why? Had I been equipped with an SLR, I would have used a beefy 500mm lens. But my digital camera's wimpy 3X optical zoom didn't have the reach I needed to shoot the scene, and the action was too small within the frame.

Finding Lenses

Don't let that happen to you. While you may not need to photograph a predator bearing down on prey in the mountains of Wyoming, you've no doubt run into situations in which a wider view or a longer zoom would have helped you take the perfect picture. Most digital cameras include a zoom range that's adequate for 90 percent of the photos people routinely take. But accessory lenses let you get rare and memorable shots that your ordinary lens can't capture.

How do you connect these lenses to your camera? That depends on the camera. A few cameras, like the Kodak DC5000, are designed to directly accommodate screw-on lenses, thanks to screw threads on the front of the built-in lens.

Those cameras are the exception, though: The vast majority of cameras need a lens adapter. Lens adapters are intermediate rings or tubes that snap or screw onto the front of the digital camera and mate with whatever lens you plan to add. Adapter rings are inexpensive and typically allow you to connect a wide assortment of standard accessory lenses to your camera.

You can find accessory lenses in a variety of places. You can start by surfing to your camera manufacturer's Web site; a local camera or computer shop might also have a selection of lenses. In my experience, though, your best bet is Tiffen. Tiffen sells add-on lenses for virtually every digital camera on the market, and their Web site makes it easy to figure out what you need to buy for your particular camera.

Power, Diopters, and Other Concerns

You can add three kinds of lenses to your camera: wide-angle, telephoto, and macro (also called close-up).

Wide-angle and telephoto lenses are identified by their X power, such as .5X, 2X, or 3X. If a lens is marked 2X, it doubles the focal length (and thus the magnification). Telephoto extensions are great for pulling in distant scenes, and obviously give you the greatest magnification when you extend the camera's built-in zoom all the way as well.

Wide-angle lenses have an X rating of less than 1; common wide-angles are .5X and .75X. Very wide lenses can distort your scene (like the fish-eye effect you've seen from extremely wide-angle lenses).

Macro lenses are used for extreme close-ups. You can use macro lenses to take pictures of coins, jewelry, and miniature figurines, for instance, or go outside and shoot bugs and leaves. Unlike other lenses, though, close-up lenses are described by diopters, which is an indirect measure of focal length. You'll typically see close-up lenses in strengths from +1 to +10, and you can screw them together to increase their strength--so a +7 and a +10 would give you a +17 magnification, which is enough to see clearly the legs on a grasshopper.

When you first start shooting with accessory lenses, watch out for an effect known as vignetting. That's what happens when, because there's an extra set of optics in the pipeline, the camera barrel actually gets in the picture and cuts off the corners of the photo. Keep an eye on the LCD display for this effect (you won't see it in the optical viewfinder) and avoid it by not going to the extreme end of the camera's zoom range.

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