| 摘要 |
An aperture mechanism of this apparatus is provided with an aperture blade which has, for example, an outline converging toward the front end with a shielding width of the front-end blade section smaller than the diameter of a ray bundle transmitted into a light guide to achieve desired dimming by shielding the light in proximity of the central region in the ray bundle earlier than that in the outer regions. Thus, a relatively narrow distribution of light will be radiated onto an observed object for a long-distance examination of smaller aperture quantities and a wide distribution of illumination light will be radiated for a short-distance examination of larger aperture quantities. In addition, the aperture mechanism may be configured to move a small-circle aperture blade which is smaller than the cross-sectional area of the ray bundle disposed on the optical axis in the direction of optical axis to shield the light in proximity of the central region in the ray bundle earlier than that in the outer regions. |
