The best new glass for your D-SLR
Most lenses these days are engineered specifically for use with digital sensors, rather than for use with 35mm film cameras. Although some hand-me-down film lenses can and do work with digital cameras, there’s been a lot of innovation to create lenses optimized for the peculiar surface of digital sensors, a surface that, unlike film, isn’t flat. A sensor is composed of millions of tiny wells, and that microscopic depth requires light to be collimated so that it strikes the pixels at the correct angle. Designed-for-digital lenses do just that.
Benefit: Because digital sensors are so precise, previously invisible lens flaws become visible. Digital-specific lenses, however, are built to even more exacting standards than great glass of just a few years ago. Today, flaws in sharpness and color fidelity are minimized.
Every manufacturer has its own terminology to describe the top-notch optical qualities of the best glass and coatings of its lenses. These terms, like SD, LD, ED and APO, describe low-dispersion characteristics.
Benefit: Low-dispersion glass and coatings minimize aberrations—the kinds of color and sharpness problems that appear dramatically amplified when images are enlarged. Internal coated elements help stop flare, and front element coatings make the glass more scratch- and dust-resistant.
ASPHERICAL AND RECTILINEAR
Aspherical lenses offer several advantages. First, they reduce spherical aberration as light passes through the lens, resulting in sharper images and reducing linear distortion in wide-angle lenses. The use of aspherical elements also allows lens designers to use fewer glass elements than they otherwise could for a given lens, making smaller and lighter lens designs possible. Rectilinear lens design makes wide angles appear more natural (and less distorted) by keeping straight lines from curving quite so noticeably.
ELEMENTS AND GROUPS
An “element” in a lens is the physical piece of glass that focuses light. Elements don’t work alone; they’re grouped together into a compound lens that achieves complex feats of focusing and resolving power.
Benefit: More elements often indicate that a lens can pull off more elaborate optical tricks (like extreme zooming), the trade-off being that lenses with more elements will be larger, heavier and, in some cases, more expensive. Every added glass surface inside the lens also increases the chance of contrast-killing lens flare, making a lens shade an even more crucial accessory.
Indicated by various acronyms depending on the brand (IS, VR, OS, VC, etc.), an image-stabilizing lens will physically shift lens elements to counteract the natural shaking that comes with handholding a camera.
Benefit: Stabilized lenses are sometimes more expensive and heavier than other lenses, but the improved stability means they can be used in lower light and at slower shutter speeds without incurring the damaging effects of motion blur. This added stability can translate to a few stops of additional “hand-holdability.”
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