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Last, but certainly not least, is the optical quality of a lens. For some discriminating photographers, this is paramount, as they want the utmost sharpness at the pixel level and they're willing to pay for it. Sharpness is affected by the quality of glass used in a lens (low dispersion, super-low dispersion, etc.), the types of coatings (ED, T* and others that fight flare to maximize sharpness and contrast) and the quantity of actual elements and groups found within a lens.
Entire articles could be written about the elements and groups within lenses, but suffice it to say, these are the high-tech constructions that mean lenses today do things that would have been considered impossible a generation ago. Conventional wisdom has long held that fewer elements and groups are preferable because it means less opportunity for lens flare and aberrations, although a look at the results from many high-quality zooms that incorporate many elements and groups shows that it's awfully hard to discern a lens' quality simply from the quantity and types of elements inside.
Other terminology you're likely to hear includes rectilinear, which means that a wide-angle lens is less likely to produce barrel distortion and keep straight lines straight at the edges and corners of the frame, and aspherical glass, which is designed to minimize chromatic aberration that affects color and sharpness. Then there's bokeh (pronounced "bo-kay"), a term popularized in recent years to describe the quality of the out-of-focus area of an image. It's commonly held that smoother bokeh is preferable, and that comes from a rounder aperture achieved by more blades on the diaphragm.
NEW LENSES FOR 2012
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