Choosing first-order group focal lengths for complex zoom lenses is a problem with too many variables to have a simple analytical solution. Furthermore, the group power balance has a large impact on performance, but there isn’t a well-known way to quickly determine the potential design performance of a given power grouping. This often leads to the choice of poor starting points increasing both the difficulty of the design process and the time to find a solution. To solve this problem (e.g. for a four-group zoom lens) a Monte Carlo like program has been written that first randomly chooses group focal lengths, finds first-order solutions, and checks for zoom group collisions. Then if a solution is valid it creates a lens design which is quickly optimized and evaluated for performance with real ray tracing using CODE V. The program keeps track of all solutions and is then able to automatically sort and identify power groupings with strong performance, simplifying the overall design process. Data collected by the program can also be used to sort solutions for minimum diameter, minimum length, and other design parameters.
The design study herein analyzes the design complexity of high zoom ratio lens systems in the visible, SWIR, and LWIR spectrums with four zoom groups (two internally moving). The aforementioned 12.5x zoom lens systems have been designed for use in the Coast Guard for maritime safety, security, and stewardship. To begin our comparative design study, the most advantageous solutions for distinct power groupings were found using a first order solution finder tool. The results showed that solutions with a PNNP, PNPP, and NPNP power grouping with the aperture stop in the third or fourth group had the most potential. At the end of the design process, a comparison was done for the three different wavebands to analyze the relative design complexity. Design complexity metrics were as follows: element count, number of aspheric surfaces, system total track length, element diameter, and tolerance sensitivity.