US Patent 6852079 Light guide and endoscope

An object of the present invention is to make the light distribution by a light guide even. In the light guide, an amount of light emitted from the central region in the light emission end face is relatively small in comparison with an amount of light emitted from a peripheral region in the light emission end face. For example, a mask for shielding light is provided near the light emission end face of the light guide. The mask is, for example, circular, and is aligned with an optical axis Z0 as the center. By providing the mask, the light emitted from the central region in the light emission end face is shielded around the optical axis Z0.