Three-component zoom lens with fixed position of optical center.

A method is proposed for calculation of initial parameters of a three-element zoom lens with an identical position of object and image principal planes of the optical system and approximately zero Petzval sum. Such an optical system has a fixed position of its optical center, which does not depend on object distance. The proposed method makes it possible to determine focal length values of individual elements and trajectories of their movements during zooming. The analysis is presented on examples of the calculation of parameters of such optical systems. These systems could be useful in optical measuring methods, photogrammetry, and machine vision techniques.