Inspection device and method of inspecting a target

摘要

An optical system (130) is provided for visually inspecting a target (131) having a variable position with respect to the optical system. The optical system includes a polarizer (132), a light modulating element (134), and a lens group (136) comprising at least one birefringent element. The polarizer converts an incident light reflected from the target into linearly polarized light. The light modulating element modulates a polarization state of the linearly polarized light in response to control signals. The birefringent element refracts the modulated linearly polarized light with a first polarization state under a first refraction index to enable inspection of the target at a first object position with respect to the optical system. The birefringent element further refracts the modulated linearly polarized light with a second polarization state under a second refraction index to enable inspection of the target at a second object position with respect to the optical system.