Some undesirable optical effects that arise from design of windshields-such as double images, distortion, astigmatism, and differential deviation of line of sight-are discussed.
The reasons for, and methods of eliminating, “ghost” images are reviewed. Curvature and tilt angle are principal design parameters available for control of ghost images. Another factor involved in double images is wedge.
Several illustrations show how cylindrically curved auto glass produces astigmatism. Glass parameters which produce astigmatism of 1/4 diopter are rather severe, however.
The amount of differential deviation depends on angle of view, and on curvature, thickness, and refractive index of the glass. It is desirable to minimize differential deviation since it may result in error in making quick assessments of traffic situations.
The author concludes that factors causing undesirable optical effects, as detailed in this paper, are understood, and means of control are under development in order to eliminate them from future glass designs.