Patent ID: 6618126
Filing Date: 2003-09-09
Classification: G01C

Abstract:
A surveying instrument having a sighting optical system and a phase-difference detection type focus detection device which detects a focus state of said sighting optical system from a correlation between a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas on an objective lens of said sighting optical system, a beam splitting optical system defining an optical path of an automatic focusing unit, the optical path of the automatic focusing unit branching off from an optical path of the sighting optical system, said phase-difference detection type focus detection device comprising:a pair of line sensors; a condenser lens group that condenses said two light bundles which are respectively passed through said two different pupil areas; a pair of separator lens groups that forms two images of said two light bundles which are passed through said condenser lens group on said pair of line sensors, respectively; wherein said condenser lens group includes more than one sub lens group, wherein said phase-difference detection type focus detection device detects said focus state of said sighting optical system on a reference focal plane which is located at a position optically equivalent to a position of a focal plane of said objective lens, and wherein at least one sub lens group of said condenser lens group is disposed on the objective lens side of said reference focal plane, and at least another sub lens group of said condenser lens group is disposed on an opposite side of said reference focal plane from said objective lens.