| 摘要 |
PURPOSE:To set an optical path length without taking the influence of a refractive index of light into consideration, by providing an additional transparent plate which is made of a material of the same quality as that of an original placing transparent plate and has the same thickness, in an optical path between a lens and a photosensitive member. CONSTITUTION:An optical system 22 contains an additional transparent plate 120 provided in an optical path between an inmirror lens 144 and a photosensitive member 2. This transparent plate 120 is fixed in an upright state between a partition plate 116 and a partition plate 122, and positioned in an optical path between the inmirror lens 144 and the third reflection mirror 146. The transparent plate 120 is made of the same material as an original placing transparent plate 102, and has the same thickness. Accordingly, a refractive index of light in case of passing through the transparent plate 102 and a refractive index of a light in case of passing through the transparent plate 120 goes to the same. |
