Study On Deformation Of Photoelectric Theodolite’s Primary Mirror Influence On The Image Under Gravity

Photoelectric theodolite is a very important measuring device in modern optical measurement in range. The Primary mirror is a very important part of photoelectric theodolite. Analyzing the primary mirror is indispensable in the design of modern photoelectric theodolite. The primary mirror of photoelectric theodolite will occur deformation under load. The deformation of primary mirror will affect the image quality of photoelectric theodolite. For increasing the imaging quality of photoelectric theodolite, it is essential to study the primary mirror.The deformation of mirror always tends to be smooth and continuous, so changes in surface shape of the mirror can be described as linear combination of independent basic function system. Zernike circle, polynomials are usually treated as basic function system, because it is weighted orthogonal, making the polynomial coefficients independent of each other. It can help to eliminate error of coupling. Zernike circle coefficients can establish contact with Seidel polynomial coefficients. Zernike circle polynomials can fit the wave-front of mirror high precision and can provide much useful information. But because the primary mirror of photoelectric theodolite has a hole in the center, Zernike circle polynomials lost orthogonal on the unit annular. The coefficients no longer have clear physical meaning and even give wrong result because of coupling. In order to improve the fitting accuracy, we must use orthogonal function system on the unit annular.This paper studies the method that using Zernike annular polynomial analyze primary mirror deformation of photoelectric theodolite. This method retains the advantage of circle and overcome its shortcome. It is used to design the primary mirror of photoelectric theodolite. The analysis result are compared with the actual result. It is show that the relative error of PV is9.2%and the relative error of RMS is10.5%.The comparing result demonstrate that the way is feasible. This paper obtain the Seidel aberration caused by the deformation of primary mirror. Custom INT file is imported to the CODE V software and getting the influence of deformation to MTF. At last the paper analyzed the influence of deformation of primary mirror under different elevation angles to the image. The result show that as the elevation increase, the PV and RMS of primary mirror deformation have decreasing trend, MTF value increases. They can provide reference to the optical system design and mechanical design.