Research

The main idea when designing an off-axis aspheric system is to establish a proper initial system and then optimize it. The optimization with optical software is important. However, a good starting point is also of great importance. There are three methods for establishing the initial system. The first uses the lens database, while the second uses paraxial optical theory. The third one is point-by-point direct design method that calculates data points on the unknown surface and fits them. W-W differential equations design method and Simultaneous Multiple Surface (SMS) design method are two widely-used point-by-point direct design methods. But both of them have a restriction on the number of FOV and aperture considered in the design process. One point-by-point design method called Construction-Iteration method has been proposed by our group. It overcomes the number restrictions of FOV and aperture compared with W-W and SMS methods. But it only applies to build freeform surfaces at the moment. Here, we need a full-field, point-by-point, direct method for designing off-axis aspheric surfaces.
So our research group has proposed a full-field, point-by-point, direct design method for aspheric systems, where light rays from different field angles and aperture coordinates are considered. Surface fitting is included during the calculations and point calculations and aspheric surface fitting is repeated continuously to calculate an unknown aspheric surface. Deviations in both the coordinates and surface normal vectors of the data points are considered to obtain accurate fitting of the surface. The calculated off-axis aspheric system can be taken as a good starting point for further optimization. The final design can be quickly obtained with further optimization from the starting point and advanced optimization skills are not required. What’ more, the proposed method is a general point-by-point method for off-axis aspheric systems that requires less design experience and makes designing off-axis aspheric system easier.