Level having an autofocus system with controllable focusing lens group

A surveying apparatus having an autofocus system through which an object to be observed through a telescope of said surveying apparatus is brought into focus,

• wherein said telescope comprises an objective lens group, a focusing lens group, a reticle and an eyepiece in respective order from a side of said object, wherein said focusing lens group is moved along an optical axis to form an image of said object on said reticle, said image formed on said reticle being observable through said eyepiece,
• wherein said autofocus system comprises:
• a beam splitter provided in an optical path between said focusing lens group and said reticle;
• first and second image forming lenses forming first and second images of said object, said first and second image forming lenses each receiving light emitted from said beam splitter;
• first and second line sensors, each having an array of light receiving elements defining a plurality of light receiving areas, said first and second images being respectively formed on said light receiving areas through said first and second image forming lenses;
• means for moving said focusing lens group along said optical axis in accordance with data output from said first and second line sensors;
• means for detecting a position of said focusing lens group;
• means for selecting, from said array on each of said first and second line sensors, at least some of said light receiving elements for use in a focusing operation in which said moving means moves said focusing lens group so as to form said image of said object on said reticle, in response to said position of said focusing lens group detected by said detecting means;
• and
• means for controlling said moving means in accordance with data output from said selected light receiving elements.