| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly reliable focal position detecting device without erroneously detecting the state of largily deviated focal position as the state of focus by forming a first a third images, detecting the second image in the state of almost bast focusing in the focusing state and detecting the first and the third images as a longer focusing state and a shorter focusing state, respectively. SOLUTION: Respective tripartite light beams divided by a prism member 8 have nearly equal light quantity to each other and are transmitted from the prism member 8 parallel to each other. The three light beams from a first image to a third image. In the state that the image forming position (focal position of an object by an objective lens 1 is almost with an image pickup plane 2 i.e., the focusing state, the focusing state, the first is in a longer focusing state, the second image is in the best focusing state, the third image is in a shorter focusing state and these states are detected by the respective line sensors 12. Consequently, since the pieces of image information of longer focusing state shorter focusing state and, in a addition the best focusing state are obtained, and erroneous detection is avoided. |
