| 摘要 |
This lens has a spherical ring-shaped zone to correct long sight and an aspherical central zone to correct short sight and mid-distance sight, said central zone having a surface of revolution which is shaped like a dome bulging out of the external side of the lens. The dome is approximately cone-shaped and its surface extends entirely on one and the same side of this cone, outside it. The height of the vertex of the dome ranges, before grinding and in the dry state, between 3 mu m and 6 mu m, and its base diameter ranges between 1.4 mm. and 1.9 mm. The generatrix of this surface of revolution comprises in succession, from the base to the vertex, a first arc of a curve with an increasing slope, a second arc of a curve with a decreasing slope, a third arc of a curve with a substantially constant slope and a fourth arc of a curve with a generally increasing slope.
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