Focus detection apparatus

A focus detection apparatus comprising:

• a light source which emits a light;
• a collimating member which converts the light into a parallel light beam;
• a light shading portion which cut off a half of the parallel light beam around an optical axis;
• a object lens which condenses the parallel light beam to the sample;
• a condensing optical system which condenses the light which has reflected from the sample ,which has not been cut off by the light shading portion through the object lens 9;
• a photodetector which is arranged at a light condensing position of the condensing optical system, has a plurality of light receiving surfaces provided thereto, and detects the light condensed by the condensing optical system on the light receiving surfaces;
• a focus detection portion which is detected focal based on the quantity of light detected by the photodetector
• a first light path along which the light emitted from the light source reaches the sample;
• a second light path along which the light reflected by the sample reaches the photodetector through the condensing optical system;
• a beam splitter which reflects or transmits therethrough the light which has not been cut off by the light shading portion in the light path, and transmits therethrough or reflects the light which has entered through the object lens in the second light path;
• and
• a restricting portion which is provided at an intermediate image forming position of the condensing optical system or near the photodetector and restricts a light detecting quantity of the light detected on the plurality of light receiving surfaces.