| 摘要 |
PROBLEM TO BE SOLVED: To allow a highly accurate measurement required for controlling an image online. SOLUTION: A common region Km is set in a paper surface reflecting region Ar, which common region Km satisfies, within a space to a lens 14, both a region K1 which is defined as a region including a light axis CL and being far from the lens 14 starting from a front focal position Fa within a region divided by a light beam passing through the front focal position Fa of the lens 14 and approximately both ends of the lens 14 and a region K2 where the paper surface reflecting region Ar should exist. In other words, only such a reflected light is received as that within a reflection angle determined by the equation tan (si)=r/fa and that within a range where the paper surface reflection region Ar should exist in consideration of an effective, diameter of the lens 14, thereby preventing a stray light incident on a photoelectric transducing element 18 to allow a highly accurate measurement. |
