| 摘要 |
PURPOSE:To always automatically correct the illuminance of the projection surface even when light source height and an original are changed by providing a dimming control part for increasing and decreasing the light quantity of a light source. CONSTITUTION:In a projection magnification measuring instrument 10, a film transmission light quantity detecting part 41 is provided on an opposite side of light source of a film holding part. The film transmission light quantity detecting part 41 detects a transmission light quantity of a film 11 and transfers a result of this detection to a dimming control part 31. As a result of detection of the film transmission light quantity detecting part 41, the dimming control part 31 increases the light quantity of a light source 12 when the film transmission light quantity is small, and decreases the light quantity of the light source 12 when the film transmission light quantity is large. In such a way, even when light source height and an original are changed, the illuminance of the projection surface can always be corrected automatically. |
