Effect of tilted metallic mesh on modulation transfer function of optical system

In order to analyze the effect of a tilted metallic mesh on the modulation transfer function (MTF) of an optical system, the relation between the MTF and tilted angle &ptheta; of the mesh was established through calculating the point spread function (PSF) of the tilted mesh using a model based on Huygens-Fresnel diffraction theory and then conducting Fourier transform on the calculated PSF. It was found through analyses that the density of triangular spikes on the MTF curve is compressed by 1/cos(&ptheta;) times along axis x, and the MTF values are degraded due to the stretch and asymmetrical distribution of diffraction spots of the tilted mesh; moreover, when the aperture of the mesh is so small that it is the optical stop itself, the cutoff frequency of MTF along axis x decreases by cos(&ptheta;) times and the MTF values drop largely. The degradation effect on MTF caused by a tilted mesh can be reduced by using a large-size metallic mesh and increasing the porosity ratio of metallic mesh.

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