Friday, May 25, 2007
Lens Design And Technology In The Age Of D-SLRs
Lens quality has grown exponentially in recent years. The optics being produced for professionals today incorporate some high-tech miracles to get the job done.
Lens technology has improved by leaps and bounds over the last 15 years. Innovations like high-tech glass, advanced apochromatic elements, optical stabilization and fast, accurate AF systems have coalesced into a set of tools that provide fantastic image quality. Prior to the 1980s, most pros avoided zoom lenses because they simply weren't up to snuff. Prime lenses were thought of as being the pro's choice because they were sharp, they exhibited fewer aberrations and they were fast.
The paradigm has changed dramatically. Today, zooms are the norm in a pro's bag rather than the exception. Exotic glass elements have reduced aberrations and increased transmission and color fidelity. The latest AF systems combined with new motor advancements and optics design make them fast and accurate to focus. Then there's optical stabilization (Canon calls it IS, Nikon calls it VR), which doesn't take the place of a tripod, but makes it possible to get shots in low light and in other situations that simply wouldn't have been possible before.
Everyone has old lenses that they simply wouldn't do without, but more and more you can rely on new lenses to surpass what the old standbys could achieve. What has changed and what's coming in the future? Here's a look at how technology is making better images possible.
Aspherical elements reduce the level of distortion and improve sharpness along the edges. These elements can optimize the focus of light coming through both the edges and the center of the lens. There are essentially three types of aspherical elements: ground, molded and hybrid.
Ground aspherical lenses are made from glass only. The grinding process of an aspherical element and the polishing process is very expensive so you only find them in top-level lenses. These are the lenses that most professionals rely on for their work. Molded aspherical lenses are produced by directly molding glass in a molding machine and incorporating a metal die. You'll typically find molded aspherical elements in lenses designed for the advanced amateur. They're less expensive to produce and well-suited to the enthusiast photographer. Hybrid asphericals are found at the lower end of the line. While they're cheap to produce and widely incorporated in consumer-grade lenses, they're usually unacceptable for pros. Hybrids consist of an aspherical glass lens that's built with a plastic surface to form the aspherical shape.
Typically, the best wide-angle lenses use a large-diameter, ground aspherical element in the front group, which helps focus light coming from a steep angle. This generalization usually holds true, but lenses are complex and many other factors can come into play. In fact, some of the very best wide-angle lenses don't incorporate any aspherical elements at all, but such lenses are the exception, not the norm.