1. Technical Field
The present invention relates to an image forming optical element that forms an erected image of an object, an image forming optical array provided with the image forming optical element, and an image reading device that reads an image of an object using the image forming optical element.
2. Related Art
In an image scanner, a facsimile, a copier, and a financial terminal device, a contact image sensor module (hereinafter, referred to as “CIS module”) is used as an image reading device. The CIS module irradiates a reading target with light, and detects reflected light at that time, to read an image of the reading target by an optical sensor. To appropriately lead the light reflected from the reading target, to an optical sensor, it is general to use an image forming optical element having image forming magnification such as erection equal-magnification. That is, the image forming optical element forms an image with the light reflected from the reading target at the erection equal-magnification, and forms the erection equal-magnification image of the reading target to the optical sensor. The optical sensor detects the erection equal-magnification image formed by the image forming optical element, to read the image of the reading target.
In JP-A-2000-066134, to improve the degree of freedom of a layout in the CIS module or to make the CIS module thin, an image forming optical element reflecting the light by each of a roof prism and a flat reflection face to change a direction of an optical axis (bend the optical axis) is proposed. The image forming optical element is provided with an object side lens that is opposed to the reading target, and an image forming side lens that forms the image of the reading target on the image forming face in cooperation with the object side lens. The roof prism is disposed on an optical path from the object side lens to the image forming side lens, and the flat reflection face is disposed on an optical path from the image forming side lens to the image forming face (optical sensor). Accordingly, the light reflected from the reading target and passing through the object side lens is reflected by the roof prism lens, a progress direction thereof is changed, the light passing through the image forming side lens is reflected by the flat reflection face, and the progress direction is changed.
In JP-A-2000-066134, the direction of the optical axis can be changed using two reflection faces (roof prism and flat reflection face) in each reflection faces. As a result, it is easy to improve the degree of freedom of the layout in the CIS module and to make the CIS module thin. However, in JP-A-2000-066134, each of lenses of the object side, image forming side lenses, and two reflection faces are separately provided, a relative positional relationship of such optical members may not be determined with high precision, and performance of forming an image of the image forming optical element may be decreased.