Surveying instrument having a sighting telescope and a phase-difference detection type focus detection device therefor

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 pair of separator lenses positioned in front of said pair of line sensors, respectively;
• a first sub lens group positioned in front of said pair of separator lenses;
• and
• a second sub lens group positioned in front of said first sub lens group;
• wherein said phase-difference detection type focus detection device detects said focus state on a reference focal plane formed between said first sub lens group and said second sub lens group, said reference focal plane being located at a position optically equivalent to a position of a focal plane of said objective lens, and
• wherein said second sub lens group is disposed on the objective lens side of said reference focal plane, and said first sub lens group is disposed on an opposite side of said reference focal plane from said objective lens.

A surveying instrument having a sighting optical system and a phase difference detection type focus detection device which detects a focus state of the sighting optical system based upon 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 the sighting optical system, the sighting optical system including a focus adjustment lens, 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, said condenser lens group comprising more than one sub lens group and being distinct from the focus adjustment lens;
• and
• a pair of separator lens groups for forming two images of said two light bundles which are passed through said condenser lens group on said pair of line sensors, respectively;
• 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.