Lens unit, lens barrel, optical device, scanner, and image forming apparatus

摘要

A lens barrel includes a communicating passage that communicates between a space inside the lens barrel and outside of the lens barrel. The communicating passage includes a through hole, a circumferential groove, and a vertical groove. Light from outside the lens barrel is prevented from entering an effective optical range of a lens through the communicating passage. A partition is arranged between the effective optical range and a non-light-transmitting range. A surface of a portion outside the effective optical range is formed of a light-absorbing material, so that light is prevented from directly entering the lens through the communicating passage.