| 摘要 |
In an image reading apparatus, an original is illuminated and an image of image information on the original surface is formed on a surface of a line sensor by an imaging system. The imaging system includes a zoom lens each element of which is so constructed as to obtain a predetermined effective F-number on a side of the line sensor of the zoom lens independently of zooming. The zoom lens has an aperture stop the diameter of which is adapted to change in synchronism with zooming to obtain a predetermined effective F-number on the side of the line sensor.
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