Optical design of two-step zoom system under visible light for a certain theodolite

Starting from the application background and the detector parameters, this paper computed the optical and structural parameters of the system. The basic design idea is dividing a large-scale and complicated system into several modules and allocating the design requirements to each subsystem reasonably. Every optical subsystem is independent, for all of them have reached almost a high image quality, as well as they can correct the aberration caused by other parts of the system. Connected the subsystems together by using ZEMAX, there formed a practical optical system of photoelectric theodolite. In the visible band of light, the aperture is 450mm, the long focal length is 4000mm with its maximum field 2ω=26.0´ while the short focal length is 2000mm with its maximum field 2ω=51.9´. The value of MTF at 501p/mm in every field is higher than 0.6. The image quality of the system is close to diffractive limit.