| 摘要 |
PROBLEM TO BE SOLVED: To shorten the time required to detect a focusing position and to obtain excellent reproducibility by calculating the focusing position of the transmitted light image of a document and adjusting the focal position of the transmitted light image of the document according to the focusing position. SOLUTION: The transmitted light image transmitted through the document T is formed on a CCD camera 17 by an objective lens (image-formation optical system) 16. The transmitted light image of the document T formed on the camera 17 is outputted to a picture display device. A control part 18 obtains the size of a projection part at the end of the transmitted light distribution intensity pattern of the transmitted light image of the document T formed on the camera 17 at one focal position, and detects the focusing position of the transmitted light image according to whether the size is within the range of a specified value or not. A piezoelectric element 19 moves a document stage 15 in an optical axis direction according to the focusing position calculated by the control part 18 so as to change the position of the document T, whereby the transmitted light image of the document T is formed on the camera 17 at the focusing position. |
