Lens Technology

Standard lenses are made from a combination of spherical lens elements. However, there can be problems with such lenses when light entering at the edges of the lens may not be perfectly focused at the same point as light entering at the center. That presents limits to performance in wide aperture and super wide-angle lenses. Lens manufacturers use aspherical glass elements in many of its lenses. In addition to correcting spherical aberration, these lenses fully correct light quantity and distortion at the edge of the image and provide excellent results when used in combination with floating elements.

Links to websites with a large number of critical and detailed lens reviews:

Digital Photography Review™ http://www.dpreview.com

Popular Photography http://www.popphoto.com/Reviews/Lenses