Focus warning system for a manually-focused still video camera having an electronic viewfinder

In a video camera providing a movie image for an electronic viewfinder and a still image for recording apparatus, the camera including an optical section for establishing an optical aperture and for focusing image light passing through the aperture upon a light sensor, the signal input of the electronic viewfinder being connected to the light sensor for obtaining the movie image, the camera further including a focus warning system for generating an internal control signal indicative of a focusing problem, the improvement in which said focus warning system comprises:

• means responsive to image light for determing the aperture necessary for the movie image in the viewfinder;
• means for determining the aperture necessary for the still image;
• and
• means for activating the control signal indicative of a focusing problem when said still aperture exceeds said movie aperture by a predetermined amount.

In a video camera providing a movie image for an electronic viewfinder and a still image for recording apparatus, the camera accepting a plurality of interchangeable lenses that are separately identifiable by indicia that interconnect with the camera, each lens providing at least one focal length and having a diaphragm for establishing an optical aperture and a focusing element for focusing image light directed through the diagphragm toward a light sensor in the camera, the signal input of the electronic viewfinder being connected to the light sensor for obtaining the movie image, the camera further including a focus warning system for generating a control signal indicative of a focusing problem, the improvement in which said focus warning system comprises:

• means responsive to the indicia of a lens for generating a focal length signal;
• means responsive to the image light for determining the aperture necessary for the movie image in the viewfinder;
• means for determining the aperture necessary for the still image;
• and
• means responsive in part to a selected focal length signal for activating the control signal when said still aperture departs from said movie aperture by a predetermined value corresponding to a reduced depth of field in the still image as compared to the movie image.

A still video camera providing a movie image of a subject for an electronic viewfinder and a still image of the subject for recording apparatus, said camera comprising:

• a light sensor;
• optical means for directing image light upon said light sensor, said optical means including a diaphragm for establishing the optical aperture presented to the image light and focusing means for establishing the depth of field relative to the subject;
• means responsive to the image light for determining a movie aperture value suitable for operation of the electronic viewfinder;
• means for establishing a still aperture value suitable for recording a still image;
• means for comparing the movie aperture value and the still aperture value;
• means responsive to said comparing means for generating a control signal whenever the difference between said movie and still aperture values is large enough to reduce depth of field by a predetermined amount;
• and
• means responsive to said control signal for initiating a corrective procedure affecting the operation of said focusing means.