Patent ID: 7961365

Claim:
An image reading apparatus, comprising: a light source which irradiates illumination light to a document; an imaging element which images reflected light of the illumination light from the document, and which satisfies a formula (1) | Bf 1− Bf 2 |<|Bf 3 −Bf 2| (1) where Bf 1 is a distance from a rear end part of the imaging element to a first imaging position relative to first light having a wavelength in a first wavelength range, Bf 2 is a distance from the rear end part of the imaging element to a second imaging position relative to second light having a wavelength in a second wavelength range, and Bf 3 is a distance from the rear end part of the imaging element to a third imaging position relative to third light having a wavelength in a third wavelength range; a color separator which performs color separation of the illumination light or the reflected light into at least three wavelength ranges including the first wavelength range, the second wavelength range, and the third wavelength range; a light-receiving element which converts the reflected light imaged by the imaging element into an electrical signal as a document image of the document, for each of the at least three wavelength ranges; and an image processor which classifies the document image on the basis of the electrical signal in the first wavelength range and in the second wavelength range; and wherein the imaging element comprises a reduction imaging element which causes reduction imaging of the reflected light; and wherein a formula (2) and a formula (3) are satisfied: | ff−fe|<|fc−fe| (2) 0.003 <| fc−fe|/fe < 0.0045 (3) where fe is a focal distance for an F-line of the reduction imaging element, and fc is a focal distance for an C-line of the reduction imaging element, wherein the e-line has a wavelength of about 546.07 nm, the F-line has a wavelength of about 486.13 nm, and the C-line has a wavelength of about 656.27 nm.