1.在Optical Coherence Tomography – Technology and Applications的第27页中，提到：
OCT imaging is performed with low numerical aperture focusing in order to have a large depth of field.
通常情况下，成像的焦深大于相干长度，这样就能保证在一定的深度下，系统能够实现相干成像。
2.在Optical Coherence Tomography – Technology and Applications的第29页中，提到：
OCM images can be obtained at different depths by adjusting the focus depth while matching the reference arm path delay to the focus depth.
所谓OCM (Optical Coherence Microscopy)，就是采用了极高的数值孔径，以至于成像的焦深小于相干长度，以此达到较高的横向分辨率。因此，这种成像方式一般为en face imaging。有一种相关的技术就叫做Full-filed OCT:
Full-field OCT performs high resolution en face imaging with coherence-gated detection using a Linnik interferometer and CCD cameras. Full-field OCT achieves cellular resolution imaging, and because a single spatial mode light is not required, it has the advantage that high axial resolution is possible using low-cost thermal or gas discharge light sources.