| 摘要 |
A low-cost, single focus lens that is formed of only four lens elements in two lens groups, one on each side of a diaphragm, is disclosed. A front negative lens group is formed of a first, positive meniscus lens element and a second, negative meniscus lens element, each with its convex surface on the object side. A rear positive lens group is formed of a third lens element that is biconvex and a fourth element that is made of plastic. The fourth optical element has relatively weak refractive power that is less than 10% that of the low-cost, single focus lens, and at least one surface of the fourth optical element is aspheric. Various conditions are satisfied so as to ensure that aberrations are favorably corrected while keeping manufacturing costs low and so as to ensure that the low-cost, single focus lens is compact.
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