OPTICAL MEASURING METHOD, OPTICAL MEASURING APPARATUS, AND IMAGE FORMING APPARATUS

摘要

PROBLEM TO BE SOLVED: To perform highly accurate measurement even when the surface to be measured of a measuring object such as paper fluctuates in the optical axis direction of a lens without being affected by the fluctuations thereof. SOLUTION: The light from a light source 41 irradiates the specific reflecting region 42 on a paper surface 37a through a lens 43 or directly. A photoelectric conversion element 44 is arranged on the rear focal surface 43b of the lens 43 to receive all of lights reflected within a predetermined angle range among reflected lights (containing scattered lights or diffused lights) from the reflecting region 42 on the paper surface 37a through the lens 43. From the light receiving output thereof, the density of the image formed on the paper surface 37a is measured. When the paper surface 37a is irradiated with the light from the light source 41 through the lens 43, the light source 41 is arranged behind the rear focal surface 43b of the lens 43.