| 摘要 |
<p>PROBLEM TO BE SOLVED: To surely discriminate an image forming point displaced in accordance with the deviation in the thickness direction of a printing plate by reducing a spot diameter in order to improve detecting accuracy and reducing interference by fine ruggedness formed on the printing plate in the case of measuring a focus position by setting the printing plate where the fine ruggedness for giving water retentivity is formed as an object. SOLUTION: An LED light source 156 is applied as the light source of a focus measuring device 150 instead of an LED light source which makes a detecting error because of the interference. The spot diameter for obtaining the detecting accuracy and power for obtaining received light quantity to a PSD 162 are previously set as the condition of application, and the LED fit to such setting is selected, so that the detecting accuracy and responsiveness are improved in comparison with those of the focus measuring device using the LED existing in the conventional manner. Thus, the device copes with the requirement of an automatic printing plate exposure device 10 to which it is applied.</p> |
