| 摘要 |
PURPOSE:To widen the visual field of the intermediate section of a successively advancing multiple focal point lens, by setting the length of the navel point curve between the center for long distance and the center for short distance to >=18mm. and the width of the surface astigmatism of the section lower than the center for short distance to a prescribed value. CONSTITUTION:A lens refracting surface has a navel point curve M which is extended vertically at almost the center of the lens and the refracting power of the lens refracting surface on the curve M gradually changes between the center for long distance (a) and center for short distance (b) and the difference between them goes to the calling frequency of a subscriber. Moreover, the cross-sectional curve of a lens refracting surface cut by a plane intersecting the curve M at right angles has an almost circular cross-sectional curve S2 of a radius of curvature equal to that of the curve M at the intersecting point of the cross-sectional curve and navel point curve at a certain point between the center for long distance (a) and the center for short distance (b), and becomes a cross-sectional curve which has a radius of curvature S1 that decreases from that of the curve M at the intersecting point of the cross-sectional curve and navel point curve M as going farther from the curve M at the section above the almost circular cross-sectional curve S2. At the section below the cross-sectional curve S2, the cross- sectional curve has a radius of curvature that increases from that of the curve M as going farther from the curve M. In addition, the surface astigmatism below the center for short distance is set to 1.0 and the maximum value of the area inside dioptre in the horizontal direction is set to (30divided by ADD)mm.. |
