1. Field of the Invention
The present invention relates to a lens apparatus including a splitting optical unit disposed on an optical path of an image-pickup optical system, for performing automatic focus based on a light beam from the splitting optical unit, and to an image-pickup apparatus including the lens apparatus.
2. Description of the Related Art
Up to now, various automatic focus techniques for an image-taking apparatus such as a still camera or a video camera have been proposed. For example, Japanese Patent Application Laid-Open No. H09-274130 discloses a lens and image-pickup apparatus in which a splitting optical unit is disposed on an optical path thereof and a focus-condition detector based on phase-difference detection is disposed on a split optical path from the splitting optical unit.
According to the still camera, after performing the automatic focus control while an aperture stop is opened, a light quantity is adjusted by stopping down by the aperture stop, and then shooting can be performed. On the other hand, taking moving picture for broadcast, video, or cinema is constantly in a shooting state, so the automatic focus control is demanded under any stop state.
In the case of shooting a moving picture, a dividing optical unit is disposed on an image side of the aperture stop and phase-difference detection is performed based on a light beam obtained by division. In such a case, when stopped down to a value smaller than a threshold value, because, for example, a subject is bright, a pupil of a secondary imaging lens is vignetted. As a result, a phase difference cannot be detected accurately, so automatic focus precision deteriorates to cause a malfunction.
When stopped down more, the pupil of the secondary imaging lens may be completely vignetted, so the phase difference cannot be detected to perform the automatic focus control.
When a dividing optical unit is provided on an object side of an aperture stop as in the first Embodiment disclosed in Japanese Patent Application Laid-Open No. H09-274130, the above-mentioned problems do not occur. However, a size of the entire optical system increases.