Thursday, October 9, 2008
Buyer's Guide 2009: Lenses
What to know about the most important part of your camera systemGLOSSARY OF TERMS
Even if you’ve mastered every aspect of how lenses work, there’s still another challenge to choosing the right lens: decoding the dialect used to describe them. Some of these terms are simple (AF means autofocus, Macro means close-focusing), but what about APO, SD, ED and LD? What’s aspherical? More elements? A 10x range? This glossary of terms should help.
APO, ED, LD, SD. Terms like these refer to the qualities of the glass, namely, low- or extra-low- or super-low-dispersion. Essentially, this glass is used to minimize chromatic aberrations—all the more important when working with a super-sensitive sensor of a D-SLR.
Aspherical. Aspherical lenses spread light more evenly to the corners of the frame. In the bad old days, the light would fall off more and more in the extreme reaches of the frame—particularly when using wide-angle lenses. Aspherical lenses are designed to provide even illumination across the sensor.
Elements And Groups. Elements are individual pieces of glass, and groups are groupings of elements working together. Essentially, a group is a compound lens. Sometimes more elements and groups are better because they allow lenses to do more specific and refined things. The tradeoff, however, is that every glass surface increases the possibility of damaging reflections or lens flare. Most notably, a lens with more optics will be larger and heavier.
HSM, USM. Codes containing the letter M often refer to upgraded focusing motors. The faster and smoother and quieter the motor, the better. It makes for a more pleasant autofocus experience when you’re neither waiting for nor listening to your lens.
IS, OS, VC, VR. These lenses have an integrated motor that moves lens elements to counteract the small movements we make when handholding a lens—movements that can cause an image to be blurry when using slower shutter speeds. The benefit is the ability to get sharp handheld shots in lower-light situations—up to a few stops below what’s normally possible.
Macro. A lens advertised as Macro (or sometimes Micro) refers to its ability to close-focus at very short distances, allowing for the tremendous magnification required to create macro images.
Rectilinear. This describes an optical design used in wide-angle lenses to keep straight lines from distorting, particularly at the edges of the frame. It’s harder to maintain parallel lines with wide angles, especially when those lines are close to the camera. Rectilinear lenses do a tremendous job of providing very wide angles of view without the distortions commonly associated with them.
Zoom Multiplier. Some zooms are described by a multiplier like 3x or 4x in marketing materials; a 30-300mm zoom would have a 10x multiplier. This number doesn’t indicate exactly how wide or telephoto a zoom lens gets, but it’s a quick way to tell how generous a range of focal lengths a lens covers. A larger range means more versatility.
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