Automatic focusing apparatus for detecting and correcting focus state of image optical system

An automatic focusing apparatus, comprising:

• a telephotographic system;
• a focus detecting device that detects a focus state of said telephotographic system based on predetermined properties of the telephotographic system;
• a focusing device that focuses the telephotographic system based on said focus state detected by said focus detecting device;
• and
• an adjustment device that compensates said focus state detected by said focus detecting device by an adjustment value to correct said defocus amount for deviations from said predetermined properties of the telephotographic system.

An automatic focusing apparatus in a surveying instrument, comprising:

• a telephotographic imaging optical system including an objective lens group, a focusing lens group, a focusing plate incorporating a reticle, and an eyepiece lens group for observing an object image formed on said focusing plate;
• a plurality of line sensors;
• a beam splitter optical system, positioned between the focusing lens group and the focusing plate, for splitting said objective light into two objective light beams forming images on said line sensors;
• a phase difference focus detecting device that detects a defocus amount of said imaging optical system, said phase difference focus detecting device including a calculation device that calculates the defocus amount based on a phase difference between the images formed on the line sensors;
• a focusing device that focuses based on the defocus amount calculated by said focus detecting device;
• an adjustment device, manually operable by an operator, that adjusts said defocus amount calculated by said focus detecting device by an adjustment value, the adjustment value being related to the defocus amount as an error due to assembly, temperature, or humidity variation, said calculation device selectively adjusting the calculated defocus amount by adding or deducting the adjustment value.

An automatic focusing apparatus of a surveying instrument, comprising:

• a focus detecting device that detects a defocus amount of an image optical system;
• a focusing device that focuses based on said defocus amount calculated by said focus detecting device;
• and
• a calibration device that calibrates a focus position error of said focus detecting device, the focus position error caused by assembly, temperature, and/or humidity, said calibration device obtaining an in-focus;
• condition by adjusting the defocus amount by selectively adding or subtracting a correction value corresponding to the focus position error.

An automatic focusing apparatus, comprising:

• an imaging optical system;
• a focus detecting device that detects a defocus amount of said imaging optical system, the defocus amount depending in part on predetermined physical dimensions of said imaging optical system;
• an external control, accessible by an operator, for setting an offset to the defocus amount;
• an automatic focusing system that focuses said imaging optical system based on the defocus amount and the offset, so that error in defocus caused by deviation from said predetermined physical dimensions are compensated by said external control.