Although it may be more fun to shop for a new camera, a new lens probably will do more to spark creativity and open new possibilities. So how do you select the perfect new lens for your photography and camera system? There's a lot to consider when weighing a lens purchase, not the least of which are those technical specifications. Even more, though, you've got to interpret those specs to figure out which ones are most important to you. Here's a rundown of what features to look for in a new lens, along with exactly why they matter, followed by a variety of great new lenses for your consideration.
The first thing any photographer learns about a lens is its focal length. Measured in millimeters, the focal length is an optical spec that, in practice, denotes whether a lens will produce a wide, normal or telephoto angle of view. The smaller the number (say, 17mm), the greater the angle of view. The larger the number (200mm, for instance), the more telephoto a lens will be. Generally (and in 35mm "equivalent" terms, which correspond to 35mm film SLRs), a wide-angle lens is shorter than 40mm (commonly 20mm, 24mm, 28mm and 35mm), a normal lens is between 40mm and 60mm (most often, a 50mm lens), and a telephoto lens is anything longer than 70mm. It should be noted that some lenses are designed specifically for APS-C sensors and won't work on full-frame cameras. Manufacturers denote this with a code like EP-S, DX or DT—or by providing an equivalent focal measurement.
Wide-angle lenses are ideal for landscapes and architecture, for expanding the view in tight quarters or for including context in a scene. Normal lenses approximate the view of the human eye, so they neither expand nor compress a scene, but this also can make them a little bit boring if you're not careful. Telephoto lenses are commonly used for portraiture (in the 80mm to 150mm range), as well as wildlife and sports photography (longer than 200mm, and sometimes upwards of 500mm, 600mm and even 800mm in the extreme) because of their enlarging power and ability to compress a scene and isolate the subject on an out-of-focus background.
Zoom Or Prime
The next consideration is whether that focal length is fixed or variable. A fixed-focal-length lens is known as a prime. Common primes are 24mm, 35mm, 50mm, 80mm and 105mm, though they can be literally any focal length. A zoom lens encompasses a range of focal lengths in a single housing. Many DSLRs are sold with "kit" lenses that offer wide to normal zooms, such as 18-55mm. Some photographers prefer a little more telephoto—say, 24-70mm—and some want extreme zooms that are capable of ranging from wide (20mm, perhaps) all the way to telephoto (upwards of 100mm and even 200mm, depending on the lens).
Why wouldn't everyone always want zooms? Because fitting a wide-ranging zoom into a single-lens body is a feat of engineering. This sometimes means compromises must be made to maximum apertures, focusing speed, optical quality or price. That's not to say they're not great lenses; there's just always a trade-off. Conversely, the trade-off for working with a usually faster prime lens is that you have to own more lenses, at more expense and weight, and take the time to change them while shooting if you want to cover a greater focal range.
Some lenses are designed to do just one specific thing. They're not likely to be used a lot of the time, but for special effects, they can be invaluable. These include macro lenses (which focus extremely close to tiny subjects and enlarge them to life-size and beyond, making them perfect for flower and insect photography, and a fun way to explore the world in miniature); fisheye lenses (extreme wide-angles that fall into two categories, rectilinear or circular, and cover an angle of view often close to or even exceeding 180º, rendered across the entire sensor or as a circle in the center of the frame); and perspective-controlling lenses (also known as tilt/shifts, they approximate the movements of a large-format view camera and help to correct perspective distortions in architectural photography or to modify the plane of focus for product photography and special effects).
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