Focus condition detection device for cameras

摘要

A focus condition detecting device of the type in which a pair of re-imaging lenses together with a condenser lens form a pair of re-images of an object image on a linesensor, such that the distance between the corresponding points of the re-images on the linesensor varies with the focus condition of a camera objective lens has an improved construction for positioning the linesensor with respect to the device with high accuracy. A field aperture mask having a field aperture is arranged optically behind a plane conjugate with the linesensor with respect to the re-imaging lenses and the condenser lens such that a pair of defocused images of the field aperture are formed on the linesensor by the re-imaging lenses and the condenser lens with respective one side blurred borders of the defocused images overlapping one another to make a V-shaped peak or dip of illuminance on a photocell of the linesensor located on the optical axis of the device, when the field aperture mask is uniformly illuminated. The device is formed into a module attachable on a camera.