Image reading device, image exposure device, and image recording device

An image reading device comprising:

• a lens;
• a solid-state image sensor which reads an original image via said lens;
• a variable aperture mechanism which is operative to change an amount of light transmitted to said solid-state image sensor from the original;
• and
• a light reducer which reduces light transmitted to the solid-state image sensor from the original;
• wherein an opening of said variable aperture mechanism is positioned in such a range that the light passing through said opening to said image sensor experiences minimal diffraction such that the light can be accurately detected by said image sensor, and said light reducer reduces light by CF which is an amount obtained by the following formula,
• CF−CTOTAL−CS
• Cs is an amount of light reduced by said variable aperture mechanism, and
• CTOTAL is a total amount of light which is required to be reduced by said variable aperture mechanism and said light reducer so that an amount of light output from said solid-state image sensor is proportional to an amount of light transmitted to the solid-state image sensor,
• wherein said range is defined by a characteristic of said lens, said characteristic of said lens being a ratio of incident light to said lens and irradiated light from said lens.

An image reading device comprising:

• a lens;
• a solid-state image sensor which reads an original image via said lens;
• and
• an adjusting portion which adjusts an amount of light incident on said solid-state image sensor from the original image so that an amount of light output from said solid-state image sensor is proportional to an amount of light transmitted to the solid-state image sensor,
• wherein said adjusting portion includes at least one variable aperture mechanism which is positioned in a range where diffraction is minimized in light which passes through said variable aperture mechanism,
• wherein said range is defined by a characteristic of said lens, said characteristic of said lens being a ratio of incident light to said lens and irradiated light from said lens.