施密特系统历史悠久，过去从三级象差理论得到的校正板方程式，也一直被人们所认同，但是此方程经光学设计软件验证后，发现a≠1／2r₀₂，其中r₀₂为校正板的顶点曲率半径，∑S₁≠0，系统的焦距和后截距也有一定的偏差，与三级像差理论不符。经过分析，发现原来从三级像差理论推导出的校正板方程式没有考虑到离焦后焦距的变化。实际上离焦后的焦距为f△=f+△。按三级像差理论重新推导可以得到新的施密特校正板方程式。由光学设计软件验证，得到a=1／2r₀₂，∑S₁=0，这与三级像差理论相符合，说明新的施密特校正板方程式是正确的。

It is well known that Schmidt system is a famous optical system. The equation of the corrector plate which was based on the third-order aberration theory was approved for a long time. When we confirmed the previous equation with optical design program ZEMAX,we found the coefficient of the equation a≠1/2r₀₂,where r₀₂ was the radius of the corrector plate vertex,and ΣS₁≠0,the focal length f and the back focal length f_b of Schmidt system also had some deviation,and didn't coincide with the third-order aberration theory. According to analysis,the cause of the errors was that the previous equation didn't contain the variation of the focal length after defocus Δ. The focal length after defocus should be f△=f+△.From the third-order aberration theory,substituting f with fΔ in calculation,we got a new equation of the corrector plate. Again,when we confirmed the new equation with optical design program ZEMAX,we could deduce that the coefficient a=1/2r₀₂,andΣS₁=0,which accorded with third-order aberration theory.