Patent ID: 8385792

Claim:
An image information detecting apparatus for detecting an overlap positional deviation of images in a color image forming apparatus comprising multiple photosensitive drums, the image information detecting apparatus comprising: a light source comprising a light emitting surface having a quadrangular shape; an image bearing member that moves in a predetermined direction; a light receiving unit comprising a light receiving surface having a quadrangular shape; an illumination optical system for causing the light emitting surface of the light source and the image bearing member to have a conjugate relationship and illuminating a pattern for detecting the overlap positional deviation, which is formed on the image bearing member, with a beam emitted from the light source; and a light receiving optical system for causing the image bearing member and the light receiving surface of the light receiving unit to have a conjugate relationship and guiding the beam reflected by the pattern for detecting the overlap positional deviation to the light receiving unit, wherein a straight line portion of a conjugate image of the light emitting surface on the image bearing member which defines a contour of the conjugate image of the light emitting surface, and a straight line portion of a conjugate image of the light receiving surface on the image bearing member which defines a contour of the conjugate image of the light receiving surface, are parallel with each other.