US Patent 12028509 Diffraction-limited optical target system with continuously-variable virtual distance

An optical target system for a device under test disposed in an optical path, the optical target system including a pupil, a lens system and a target configured to be adjustable in position along the optical path such that the object distance of the target with respect to the lens system, is adjustable, the lens system is disposed between the pupil and the target along the optical path, wherein a first virtual image cast behind the target is of a first size when the target is disposed at a first position along the optical path, a second virtual image cast behind the target is of a second size when the target is disposed at a second position along the optical path.