| 摘要 |
PURPOSE:To compensate the illuminance surely, by providing a non-mirror part in a mirror, where the use effective width is extended according as magnifications are changed from a high value to a low value, so that the illuminance in both ends are lowered in accordance with the change to low-value magnifications. CONSTITUTION:When a width where the luminous flux in the equal-magnification copy is projected to the surface of the fourth mirror 4 is denoted as (l) and a width where the luminous flux in the minimum-magnification copy is projected to the surface of the fourth mirror 4 is denoted as l' (l'>l), the reflection part of the fourth mirror 4 is formed to a shape like a sandglass where the width of the center part is l' and that in both end parts is l, and the outside part is non-reflective. In the minimum-magnification copy, the fourth and the fifth mirrors 4 and 5 and a lens 7 are moved and set to positions indicated by dotted lines. All of the luminous flux is reflected in the reflection part of the mirror 4, and only the luminous flux of a ratio l/l' is reflected in the reflection parts in both end parts. Thus, the rise of the peripheral illuminance for reduced magnification is stopped, and a photosensitive drum 9 is irradiated with the light having a constant illuminance distribution. |
