In a single lens reflex camera interchangeably using two types of interchangeable lenses, i.e. for open photometry and for stopped-down photometry, and having an exposure determining device capable of measuring light by a system suited to each of the two types of lenses, a misfunction preventing device comprises a different discriminator member provided in each of the lenses and cooperable with manually operable aperture means to control release blocking means so that shutter release may be prevented when an inappropriate photometric operation has been effected.

A photographic camera comprises an objective lens having a preselectable aperture diaphragm, a diaphragm preselection setting device, an exposure measuring circuit including a moving coil, a photoelectric cell, a power source and a voltage adjustment device having a sliding contact, an entrainment member on said preselection setting device effective to move said sliding contact, and stop means for effecting arrest of said sliding contact in a position in which the electrical value corresponding to the photometric initial diaphragm is determined by the voltage adjustment device, the entrainment connection between the entrainment member and the sliding contact being nullified on arrest of said sliding contact.

An automatic exposure control apparatus of electric type for a photographic camera having an exposure control parameter setting means cooperative with a geometrical progression scale in isometric graduation is provided with a resistor device. The device includes a variable resistor having a grounded slider associated with the setting means upon movement thereof for providing a resistor value proportional to the amount of movement of the setting means, but to the reciprocal logarithm of the preselected parameter value. In order to minimize the complexity of a computer circuit responsive to the various outputs of the resistor device for performing photographic Appex computation, a bias voltage is applied to each of the variable resistors in a manner to produce a signal in the form of current proportional to the reciprocal of the amount of movement of the setting means. The resistor device has a single substrate having a plurality of resistor elements formed thereon by a metal coating technique and arranged for cooperation with respective sliders, thereby improving the exposure control accuracy and stabilization of the performance of the computer circuit against variation of temperature distribution in the apparatus.

In a single-lens reflex camera of the TTL metering type, light passed from an object to be photographed through the open aperture in a photographic lens is measured and a correction member provided in the interchangeable photographic lens automatically corrects a vignetting error produced during the TTL metering while shifting the scale plate mounted within the viewfinder for indicating the maximum relative aperture of the lens, whereby the indication of the initial aperture value of the lens and the correction of the metering error are performed simultaneously upon mounting of the interchangeable lens.

A system for controlling an aperture of a lens including an adapter for mounting the lens onto a camera body. The adapter includes a ring having an internal gear, and an aperture control bar formed on the ring. Another gear is provided which meshes with the internal gear. The aperture control bar contacts an aperture control lever of the lens, while the other gear is driven by a motor driven AF coupler of the camera body to rotate the ring. The rotation of the ring rotates the aperture control bar, which moves the aperture control lever of the lens. The size of the aperture of the lens is changed when the aperture control bar is moved.