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Choosing Digital Camera Lenses

Take The Guesswork Out of Choosing An Interchangeable Digital SLR Camera Lens
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Interchangeable Digital SLR Camera Lenses

So you’ve made the leap from a point-and-shoot pocket camera to a digital SLR. Or perhaps you’ve upgraded an old manual film SLR for something a little higher-tech. Now you’ve got a problem: to get the most out of that new camera, you’ve got to choose the right interchangeable SLR lenses to go with it.

Manufacturers are constantly making improvements to interchangeable lenses—both in the glass that goes inside and in the extra features that make them more user-friendly. What, where, when and how you shoot will determine the features that are most important to you.

Normal, Wide And Telephoto
The first step in choosing the right lenses is to understand the different effects created by wide-angle, normal and telephoto lenses. Sure, everyone knows that a wide lens shows much more of a scene, and a telephoto allows you to get up close for details, but that’s just the tip of the iceberg.

A wide-angle lens spreads the scene apart, creating the impression of more distance between subjects that actually may be closer together—à la “objects in the mirror may be closer than they appear.” By getting close to a foreground subject with a wide-angle lens, you’re still able to incorporate the surroundings into the shot. This can add a tremendous sense of context in your images. Wide-angles also provide greater natural depth of field than longer lenses, so it’s easier for the average shooter to keep the scene sharp. They’re used every day by architectural and landscape photographers who need to show complete interiors or structures when they can’t get far enough away to use a normal lens.

A normal lens is designed to provide a natural perspective like the human eye sees. In the 35mm film format, normal is anywhere from 40mm to about 55mm, with 50mm being the most common option. They’re great for many situations, but they just can’t expand a scene the way a wide angle of view can, nor can they condense elements like a telephoto.

Choosing An Interchangeable LensThere’s a discomfort that comes from someone sticking a lens right in your face. That’s why a telephoto lens is ideal for portraits; they allow the photographer some distance from the subject. Also, because they compress the background and produce an inherently shallower depth of field, they’re perfect for simplifying a composition in order to draw attention to the subject. In addition to portraiture, telephoto lenses often are used when small or faraway objects need to be enlarged. That’s why they’re so common among bird photographers, sports shooters and journalists.

For concentrating on small objects, however, a telephoto alone won’t do it. Macro and micro lenses allow focusing as close as a few inches from the subject; a standard telephoto lens may only focus at a few feet. Generally, the longer the focal length of a lens, the farther away its closest focusing point will be.

Choosing An Interchangeable LensZoom Or Prime?
Ideally, you’ll have lenses to cover wide-angle, normal and telephoto perspectives. Do you want to buy multiple lenses, or would you rather have them all rolled into one? Even though they’re commonplace today, zoom lenses once were the technical marvel of photography. Instead of needing five different lenses to cover the range from wide-angle to telephoto, suddenly one lens could do the job.

For the amount of range that they cover, zoom lenses are lighter and more portable than fixed-focal-length, or prime lenses. Just by virtue of carrying, say, one 28-80mm zoom instead of individual 28mm, 35mm, 50mm and 80mm prime lenses, you’ve lightened your load immensely and you’re pretty well prepared for any situation. That’s why zoom lenses are so popular for the average photographer. So why do they even make prime lenses anymore?

While a zoom lens offers the added benefit of allowing you to zoom in close for critical focus before widening out to complete the shot, prime lenses have benefits of their own. Conventional wisdom was that prime lenses were sharper than zooms, but with all the improvements in lens construction, that’s no longer necessarily the case. Many pro-level zooms (which also carry a pro-size price tag) can be just as sharp or sharper than some prime lenses. This sharpness difference often is imperceptible to the naked eye, however. If you’re not planning to sell mural-sized prints, perhaps that extra sharpness isn’t worth the extra price.

Prime lenses and zoom lenses also differ in the number of elements (or individual pieces of glass) contained within the lens. The more elements in a lens, the more susceptible it is to lens flare, which leads to less contrast, flatter colors and even a loss of perceived sharpness. Complex zoom lenses often incorporate more elements than a prime lens, which makes them inherently more susceptible to flare.

Choosing An Interchangeable LensFlare is most commonly combated with a lens hood at the end of the barrel to keep stray light from entering the lens at off angles. With a prime lens, the hood is designed for that single focal length. But with a zoom lens, the hood has to accommodate both ends of the lens’ spectrum. To do this, many zoom lens hoods are flared to allow for as much coverage as possible without the hood creeping into the corners of the frame.

Apertures And Lens Speed
The maximum aperture of a lens, or how wide it can open, also is referred to as the speed of a lens. That’s because the more light that can enter a lens, the faster the shutter speed you can use.

When shopping for a lens, the maximum aperture is the ƒ-stop that’s shown in the name, so a 20mm ƒ/2.8 lens has a maximum aperture of ƒ/2.8. If you’re new to apertures, the number—in this example, ƒ/2.8—actually is a ratio, so the smaller the number, the larger the maximum aperture opening. Larger apertures let in more light and, hence, are “faster.”

Choosing An Interchangeable LensA lens’ speed is most commonly a concern for photographers who shoot fast-moving subjects (like sports or animals) or for those who shoot in low-light situations. If most of your photography doesn’t involve fast-moving subjects or twilight compositions, a large maximum aperture may not be much of a concern. But if you’re planning to shoot Friday night football games for the local newspaper, a fast lens will make your job much easier.

Some zoom lenses list a range of maximum apertures; for example, a 28-135mm lens might have a maximum aperture of ƒ/4-5.6. This variable ƒ-stop means that at the lens’ widest focal length (28mm), the maximum aperture will be ƒ/4, but when zoomed in to 135mm, the lens’ maximum aperture is reduced to ƒ/5.6.

Though a disadvantage in terms of speed, variable aperture lenses offer a big advantage on price. Constant maximum aperture zoom lenses require more (and bigger) elements, making those lenses both heavier and more expensive. If the low-light possibilities of a faster lens are important, a fast and constant maximum aperture is probably better for you; if not, you can save a considerable amount with a variable maximum aperture.

But My Camera Is Digital!
All of these topics are equally pertinent for film and digital cameras. Lenses designed for 35mm may behave differently than you expect when you attach them to your digital SLR, however. That’s because many digital SLRs use a sensor that’s smaller than a 35mm frame. That means that the imager is only seeing part of the full frame for which your lens is designed. This effect—like cropping to the middle of a 35mm frame—is known as the focal length magnification factor. In most cases, this factor is somewhere between 1.3x and 1.6x, depending on the sensor’s exact size.

A 1.6x factor will turn a 100mm lens into a 160mm lens. That’s great! Now you can get even closer without having to buy a longer, heavier telephoto lens. True, but the problem occurs when you want to get a wide angle. Suddenly your 28mm lens is more like a 45mm lens—not very wide at all!

The good news is that manufacturers have addressed this by introducing even wider lenses designed specifically for smaller digital sensors. They’re extra-wide focal lengths—in the realm of 12mm to 16mm—that become much more versatile 18mm to 25mm lenses when used with the camera’s smaller sensor.

Letters, Numbers And Other Strange Abbreviations
If you walked into a camera store tomorrow and asked for a lens, you’d obviously have focal lengths and primes and zooms from which to choose. But you’d also be confronted with lenses that are IS, VR, APO, T*, ED, LD, SLD… Now what?

An IS or VR lens is “image-stabilized” or “vibration-reducing,” depending on the maker. The result is the same, however: you effectively can use slower shutter speeds in lower-light situations because the lens is motorized to counteract the natural shake your hands produce. It’s not as good as a tripod, but it’s much better than trying to hold a non-IS/VR lens if you’re tracking a fast-moving object or shooting with a long lens in low light. (To minimize blur caused by camera shake without an IS/VR lens, choose a shutter speed at least the length of the lens you’re using—1⁄125 sec. or faster for a 125mm lens, 1⁄30 sec. or faster for a 30mm lens, and so on.)

ED, LD, SLD, APO and T* each denote some form of low-dispersion or ?coated glass. The specifics vary by the manufacturer, but the point is that these lenses, with one or more special coatings on the elements, help to improve color fidelity, sharpness and contrast.

Aspheric glass is most commonly needed with wide-angle lenses because it denotes that the glass is specially designed to maintain critical sharpness even at the edges of the frame. A rectilinear lens is similar, but instead of maintaining focal sharpness at the corners, these lenses keep straight lines straighter at the edges, eliminating the barrel distortion inherent in wide-angle glass.

Choosing An Interchangeable Lens
Budget, Pro Or Something In Between?
Let’s say you’ve decided that the perfect lens for you is a 28-105mm ED IS lens. Problem solved, right? Not quite. Although you may have a Canon or Nikon or Olympus camera, you’re not limited to lenses from those manufacturers. Third-party manufacturers including Sigma, Tamron and Tokina offer lenses that fit a variety of mounts. The best thing about these lenses is that the manufacturing technology is so advanced today that even many non-professional lenses are tremendously sharp and remarkably affordable. In many cases, you can get two third-party lenses for the price of one pro lens.

Professional lenses often are very fast and very sharp. The trouble is that they also can be very expensive. Money’s no object? Lucky you, but a pro lens still might not be the right answer for your needs. Particularly with long telephotos, pro lenses can be cumbersome and heavy. Those sports photographers on the football sidelines are using giant lenses with very large maximum apertures. If you don’t want to lug around a seven-pound 300mm lens all day, perhaps a standard lens is more appropriate for its portability—at least until you land that gig at Sports Illustrated.

Accessory Lenses

Just because you have a fixed-lens digital camera doesn’t mean you can’t gain new focal lengths. With most advanced digital compact cameras, you can make your lens see wider, increase its magnification or add special close-up lenses that will let you focus close with the entire range of the camera’s zoom.

Canon, Fujifilm, Nikon, Olympus and Sony all make dedicated accessory lenses for their cameras. These lenses either screw into the filter ring on the camera lens or fit special adapters around the zoom so the lens can continue to move in and out. The adapters also allow you to use filters on the cameras.

Most built-in zooms for digital cameras don’t get very wide compared to what you can achieve with a digital SLR. This makes wide-angle accessory lenses a great first addition to your camera system. Typically, they come in strengths of 0.6x to 0.8x and offer a 25% to 40% widening of the angle of view. A camera with a 35mm equivalent of 28mm would have a 22mm equivalent with a 0.8x lens, for example. Nikon has been aggressive in developing excellent wider-angle lenses for its Coolpix line and still has the best selection of any manufacturer.

Wide-angle accessory lenses also are marketed by a variety of independent companies, including ProOptic, Tiffen, Kenko and Century Optics. One challenge with all of these is that the manufacturers have to make lenses that theoretically work with all cameras, compared to dedicated lenses from a manufacturer designed for that specific camera and lens.

Therefore, it’s difficult to say which independent lenses will work well with a particular camera and which won’t; you have to try them. Plus, the wide-angle setting of the zoom sometimes acts out of character even with good accessory lenses because of the angle of how light passes through the add-on lens. You easily can find a lens that’s superb on one camera and worthless on another.

Olympus 8080Century Optics, for example, has a 0.3x full-frame fish-eye that requires you to set your lens to its macro setting to focus properly. Even then, it’s not unusual to see color fringing along the lines at the outer parts of the image area. The wide-angle effect is so strong that this might not be important, but now Photoshop CS2 can correct color fringing in Camera Raw (and most advanced digital compact cameras can shoot RAW).

You also can purchase telephoto accessory lenses. Typically they add 1.5x to 2x magnification to the original zoom and must be used with the telephoto at its maximum setting. Because the angle of light is pretty straight between the camera lens and add-on lens, there’s less of a challenge in matching these lenses to the zoom. All of the companies mentioned here have them, although Nikon and Olympus have the greatest range, offering accessory lenses up to 3x for some of their models. In addition, Kenko has a special 8x monocular accessory lens that produces dramatic results for certain cameras.

Special high-quality, multi-element close-up lenses, also called achromatic close-up lenses, will further increase your possibilities with a digital camera. These allow extremely high-quality macro photography with all focal lengths of your camera (way beyond the built-in close-up setting). They can be especially useful, as the close-up setting for most digital compact cameras is restricted to a single focal length. These lenses are available in a variety of strengths from Canon, Century Optics, Hoya and Nikon.

One nice thing about all accessory lenses is that their construction is pretty much just glass and mount. This means manufacturers can make them small, lightweight and relatively inexpensive.