According to the approximate calculation theory of the amplitude distribution of coherent optical imaging, the imaging system is a linear space invariant system, and the transfer function of the ocular circle is defined as the filter of the geometrical optical image spectrum. Using the theory for accurately calculating the amplitude and phase distributions of image optical field, we found that the imaging system was no longer a linear space invariant system and that the physical definition of the transfer function needed to be modified. Through simulation and optical experiments of single lens coherent optical imaging and digital holography imaging, we verified the new definition of the transfer function as a spatial filter for geometric optical images diffracted by Fresnel lenses at a specific distance.