近年来，基于热光场的鬼成像在理论和实验上得到了广泛的关注。研究了探测器尺寸大小以及探测光路距离不相等(即散焦)对无透镜鬼衍射成像的影响。在以前的理论工作基础上，对无透镜鬼衍射成像的强度关联函数做了进一步的分析，发现散焦的效果相当于使物体的透射函数在相位上有一个啁啾调制，而有限大小的探测器则使得无透镜鬼衍射系统等价于一个部分相干成像系统，两者都会引起成像质量的降低。通过计算不同条件下的成像相关度，定量分析了不同参数下的无透镜鬼衍射的成像质量，为具体的实验设计提供定量的帮助。

Recently, ghost imaging with thermal light attracts a lot of attention both theoretically and experimentally. The effects of the detector size and defocusing length on lensless ghost diffraction are investigated. Through analyzing the intensity correlation function of lensless ghost diffraction, the defocusing will lead to a chirp modulation on the phase of the transmission function of the object, while the finite size of the detector makes the lensless ghost diffraction system equivalent to a partially coherent imaging system. These effects lead to the degradation of the imaging quality. Via calculating the correlation of the idealized images and realistic images under different conditions, the dependences of diffraction qualitites on different parameters are quantitatively analysed, so that the results may be used to provide quantitative references for realistic experiments.