Atoric镜片设计
作者:GREGORY L. STEPHENS and JOHN K. DAVIS
译者: Lisa Huang
原文出处:http://www.eyecalcs.com/DWAN/pages/v1/v1c051b.html#ato
Atoric镜片是目前市场上最新的镜片设计。它的前表面可以是球面的也可以是非球面的,但镜片的后表面为了矫正散光,是一种atoric非球面,而非复曲面。与标准复曲面一样,这种atoric后表面有两条主子午线,但在每条主子午线上的切面形状都不是圆形。Atoric镜片比同样材质、同样度数的球面镜片更平,更薄,更轻,但使用atoric镜片的主要原因是为了提高球柱镜的离轴成像质量。Atoric镜片的离轴像要比设计良好的球面镜或非球面镜都更好。
正如之前提到的,镜片设计师在矫正球柱镜的离轴光学时会遇到问题。矫正视野误差只有一种基弯,但有不同度数的两条子午线,且每条都有各自的弧失和正切误差。镜片设计师必须折中选择一个基弯,从而最小化模糊度,即两条子午线误差的加权平均值。Atoric后表面的使用可以帮助设计师不用考虑这个折中。设计师可以通过分别研究后表面上的各条子午线,来选择可以最好矫正离轴误差的非球面子午线形状。每条主子午线的最优非球面形状通常是不同的,所以atoric成品镜片的背面会是两种不同非球面曲线的复杂结合。
非atoric设计的折中选择会造成较大的视野误差,而atoric设计对散光矫正有着很大的好处。但是atoric表面的曲线很难制作。由于所需技术相对较新,美国大部分光学实验室都没有能力铣磨出atoric后表面。只有镜片生产商有必要的设备。生产商提供的未切割单光atoric镜片可以由光学实验室进行割边。少见的镜片度数和多焦点镜片(正常情况下由光学实验室从半成品毛坯加工而来)必须由镜片生产商定制而成atoric镜片。
现在市场上至少有四种atoric镜片设计,Sola ViZio单光镜片,Optima Hyperindex 166单光镜片,Rodenstock Multigressiv 2 渐进多焦点镜片,和Zeiss Gradal Top渐进多焦点镜片。随着生产商和实验室对镜片加工技术的改进与生产成本的降低,atoric镜片会变得越来越常见。非球面设计和atoric设计的优点预示着将来大部分镜片都会至少有一面是非球面或atoric。
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