Complex sentence: Translucent objects, like a living human cell, that absorb or scatter small amounts of light and just induce a phase shift can only be made clearly visible by using a Zernike or a Nomarski phase contrast microscope.
Split into simpler sentences: Translucent objects, like a living human cell, absorb or scatter small amounts of light. Such objects do, however, induce a phase shift that can be observed using either a Zernike or a Nomarski phase contrast microscope.