1. Field of the Invention
This invention relates to a light shielding mechanism for a quadrilateral opening and more particularly to a light shield mechanism for such an opening within a single lens reflex camera and the like.
2. Description of the Prior Art
In single lens reflex cameras, provided with a mechanism for automatically determining the aperture size or the extent of the exposure time or similar parameters in accordance with photographing conditions such as the brightness of the field to be photographed, the camera employs an internal light receiving photometric system in which a photosensitive portion for measuring the light within the field to be photographed arranged within the region of the light path emanating from the field to be photographed and transmited through an image lens in order to determine the aforementioned parameters for film exposure. However, it is not possible to disregard the influence of counter-incident light which falls on the light path from the eyepiece portion of the view finder optical system. Particularly where the eye piece portion is exposed when the photograph is taken by means of a self-timer or remote control mechanism, a relatively large error is produced by the presence of the counter-incident light acting on the light being measured relative to the field being photographed.
For this reason, it is often required that a mechanism be provided for shielding the view finder eyepiece in single lens reflex cameras and the like, and it is further necessary to add such a mechanism for shielding a light projection optical system when a slide change is being effected within a slide projector to thereby enhance projection effects, and similarly it is often required that such a shield mechanism be provided within optical illumination systems in telescopic photograhic apparatus or the like.
It is, therefore, an object of the present invention to provide a light shield mechanism for a camera view finder eyepiece and the like which reduces the area of the shield blades incorporated within said mechanism where the optical path across which the light shield is employed comprises a quadrilateral opening such as a rectangle or the like.
It is a further object of the present invention to provide an improved shield mechanism which minimizes the space required for the shield blades within the periphery about the quadrilateral light path opening and to provide a light sield mechanism which is both simple in construction and which readily attains the desired light shielding function.