| 摘要 |
PURPOSE:To facilitate fitting and manufacture and to make corrections for long distance and short distance by employing a spherical surface as an internal surface and a special aspherical surface as an external surface. CONSTITUTION:The special aspherical surface J consists of a curved surface which is divided internally in 1:k proportion and formed of a trace of intersections of a spherical surface H and a normal line as internal division points when it contacts the spherical surface H and a secondary curved surface I (eccentricity E) of rotation having the same radius of vertex curvature at a vertex and the distance of the normal line to the spherical surface from the spherical surface and secondary curved surface of rotation is 1. Then, a coefficient (k) and the eccentricity E of the secondary curved surface of rotation are varied to obtain various curves of the special aspherical surface, and the increase degree of plus frequency is determined optionally from the center part of the lens to the peripheral part. Then, the internal spherical surface P of the lens is worked by a normal method and the external surface is worked by using a copying lathe and a templet for the secondary curved surface of rotation. Thus, corrections for long distance and short distance are made. |
