Patent ID: 8159673

Claim:
A light amount detector, comprising: a light emitter configured to direct light onto a detection pattern formed on a detection surface of an image carrier; a light receiver configured to detect diffused light reflected from the detection pattern; and a light amount detection unit configured to detect an amount of light received by the light receiver based on detection output of the light receiver, wherein one of the light emitter and the light receiver being provided at a position directly opposite to the detection surface, such that a distribution of sensitivity of the light receiver detecting the diffused light is substantially symmetrical with respect to a detection output peak when the detection surface is substantially parallel to a hypothetical line connecting the light emitter with the light receiver, and based on the sensitivity distribution of the diffused light sensor, evaluated values of a plurality of patterns are obtained such that a ratio of the evaluated values defines an allowable range of angles between an optical axis of the light emitter and a normal line to the detection surface.