1. Field of the Invention
This invention relates to television cameras, and more particularly to a bias-light emitting device for use in an optical system of a television camera in which a light guiding means having an entrance aperture adjacent a light source is provided with a diffraction grating formed in the total internal reflection surface of the guiding means for diffracting a fraction of the light rays being guided therethrough, and for directing the fraction toward the image pickup tube.
2. Description of the Prior Art
There are known television cameras employing bias-light devices, as, for example, in U.S. Pat. No. 3,610,818, where a half mirror is disposed between the objective lens and the image pickup tube, with the reflecting surface thereof being inclined from the optical axis of the objective lens to direct light from a bias-light source positioned outside of the optical path thereof to the image pickup tube. This arrangement, however, has a drawback that a relatively large space is necessary for the provision of the half mirror in the optical path of the system.
U.S. Pat. No. 3,767,846 discloses another type of bias-light emitting device in which a number of acrylic resin rods are employed to transmit illumination light from the outside of the optical path to the image pickup tube. The employment of rods, however, limits the possibility of increasing the light emitting area.