Image pickup apparatus and method of controlling the same

An image pickup apparatus for picking up an image of an object for imaging a motion picture and a still picture in a motion picture mode and a still picture mode, respectively, comprising:

• a diaphragm for intercepting partially or wholly incident light rays;
• a charge coupled device for photoelectrically converting said incident light rays on a pixel-by-pixel basis and storing temporarily electric charges resulting from said photoelectric conversion, said charge coupled device outputting mixedly the electric charges from every pair of vertically adjacent pixels in the motion picture mode while outputting the charges from the individual pixels independent of one another in the still picture mode;
• electronic shutter means for sweeping out said charges from said charge coupled device at a given timing;
• processor means for forming a video signal by processing the electric charges outputted from said charge coupled device;
• an arithmetic circuit for arithmetically determining an amount of exposure on the basis of said electric charges;
• a control circuit for controlling said diaphragm and said electric shutter means such that a total amount of exposure in said still picture mode is determined and an amount of exposure for each field in said motion picture mode is determined;
• exposure control means for allowing said electronic shutter means to sweep out the electric charges from said charge coupled device and then to stop said sweep-out of the charge in synchronism with a closing operation of said diaphragm for thereby controlling the amount of exposure in said still picture mode;
• means for holding a characteristic curve representing a characteristic of a relationship among brightness of the object to be picked up and an iris value of said diaphragm and a shutter speed of said electronic shutter, said characteristic indicating reduction of an aperture diameter of said diaphragm and increase of the shutter speed when the object to be picked up is bright, and indicating increase of aperture diameter of said diaphragm and reduction of the shutter speed when the object to be picked up is dark, so as to maintain the shutter speed which adjusts for an error relating to a closing operation of said diaphragm;
• and
• iris value/electronic shutter speed control means for controlling the relationship between the iris value of said diaphragm and the shutter speed of said electronic shutter on the basis of the characteristic curve held by said holding means, and in accordance with illuminance of said incident light rays in said motion picture mode;
• wherein after said electric charges are swept out by said electronic shutter means, said diaphragm in the still picture mode is closed from the last aperture of the diaphragm obtained in the motion picture mode which varies in accordance with the brightness of the object in the motion picture mode.