在对随机弱散射屏进行表面参数的原子力显微镜测量和建立了门积分取样平均的随机光强自相关函数测量系统的基础上，对弱散射屏在严格像面和离焦像面上产生的散斑自相关函数进行了测量。发现在严格像面上，散斑平均颗粒的大小随表面粗糙度增加而减小，且光强自相关函数次极大的相关间隔宽度随粗糙度增加而减小；而次极大的起伏随粗糙度的增大而增大；在离焦像面上，离焦量的增加使光强的自相关函数下降变得平滑，并使极小值点和次极大点变得不明显或者消失。

By measuring the parameters of weak random screens with AFM and constructing a specially designed setup with gated integrator, the properties of autocorrelation functions of speckle fields produced by weak random screens on the focused and defocused image planes are studied experimentally. It is found that: 1) as the surface roughness increases, the average size of the speckle grains on the focused image plane decreases, and the spatial separation range of the secondary maximum of the autocorrelation functions is reduced while its fluctuation is increased; 2) as the defocus increases, the autocorrelation function of the speckle intensity on the defocused image plane decreases more smoothly and the first order minimum and the secondary maximum become indistinct or even disappear.