| 摘要 |
A multi-element photographic lens has a strongly aspheric surface formed on a strong lens element that is movable relative to the other elements along a common optical axis. The aspheric surface corrects at least the lower order aberrations contributed by the movable element thereby allowing the movement to focus the lens over a wide focus scale or object distance. Preferably, the elements are formed of plastic, the movable element is a front element, and at least one other aspheric surface is formed on a lens element.
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