Charman W N
Ophthalmic Physiol Opt. 1982;2(1):75-86. doi: 10.1016/0275-5408(82)90049-7.
The first-order design characteristics of a concentric varifocal lens consisting of a circular reading portion and an outer distance portion, each of contrast power and separated by an annular zone where the sagittal power decreases linearly with zonal radius, are analysed. It is shown that, while such a lens can either be constructed in homogeneous material of varying thickness (the Beach lens) or with a cylindrical gradient of refractive index and a constant lens thickness, substantial amounts of unwanted astigmatism in the transition zone are intrinsic to the design and to other forms of concentric varifocal. These theoretical results are compared with available practical measurements on Beach lenses.
分析了一种同心变焦透镜的一阶设计特性，该透镜由圆形阅读部分和外部远用部分组成，每部分具有不同的屈光度，并由一个环形区域隔开，在该环形区域中，矢状屈光度随区域半径线性减小。结果表明，虽然这种透镜既可以用厚度变化的均匀材料制成（比奇透镜），也可以用折射率呈圆柱梯度且透镜厚度恒定的材料制成，但在过渡区域中存在大量不需要的像散是该设计以及其他形式的同心变焦透镜所固有的。将这些理论结果与比奇透镜现有的实际测量结果进行了比较。
