求翻译：阿贝成像原理认为，透镜的成像过程可以分成两步：第一步是通过物的衍射光在透镜后焦面(即频谱面)上形成空间频谱；第二步是代表不同空间频率的各光束在像平面上相干叠加而形成物体的像。成像过程的这两步本质上就是两次傅里叶变换。是什么意思？

Abbe principle that the lens of the imaging process can be divided into two steps: The first step is the formation of the spatial frequency spectrum in the matter diffraction optical lens focal plane (ie the spectrum of the surface); The second step is to represent different spatial frequency