Automatic focusing apparatus with plural light receiving devices for a surveying instrument
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorsShinichi Suzuki, Masahiro Nakata
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Abstract
An automatic focusing apparatus includes a telephotographic system and a focus detecting device which detects a focus state of a plurality of variable sized, symmetrically shaped focus detecting portions by designating a center of a visual field of the telephotographic system as a center of the focus detecting device. A judging device judges a narrowest focus detecting portion as being effective among the focus detecting portions and which obtains a reliability of at least a predetermined value.
Claims12
An automatic focusing apparatus of a surveying instrument, the automatic focusing apparatus comprising:
- a telescopic optical system comprising:
- an objective lens group;
- a focusing lens group;
- a focusing plate having a collimation axis;
- an eyepiece lens group for viewing images of objects formed on the focusing plate;
- a beam splitting optical system located between the focusing lens group and the focusing plate;
- an AF sensor defined by a plurality of light receiving devices comprising focus detection portions, the plurality of light receiving devices being located within an optical path split by the beam splitting optical system, and the center of the plurality of light receiving devices corresponding to the collimation axis of the focusing plate;
- and
- a judging device for checking the contrast of each focus detection portion of the plurality of light receiving devices;
- wherein the judging device initially detects a contrast of a largest focus detection portion of the plurality of light receiving devices, and when a contrast greater than a predetermined value is obtained, a contrast of the other focus detection portions of the plurality of light receiving devices are detected, in order from a smallest to a largest of the focus detection portions;
- and
- wherein the automatic focusing apparatus calculates an amount of defocus by utilizing, as the AF sensor, the focus detection portion of the plurality of light receiving devices which has obtained an effective contrast of the smallest focus detection portion deleted by judging device, wherein the focusing lens group is moved according to the amount of defocus calculated.
Dependencies are inferred from the claim text.