Passive focus sensor.
A focus-sensor module for large-format photographic cameras has been developed that permits the measurement of defocus at any location of interest in the image field. The focus sensor employs passive triangulation through a split imaging aperture. The main difference between commercial autofocus modules with fixed-measurement positions and the new module is that the imaging aperture is subdivided into more than two fields to compensate for the unknown location of the defocus measurement. At ƒ/5.6 the focus sensor shows a maximum resolution in defocus of approximately 0.1mm at the image side at levels of illuminance in the recording plane ≥0.01 lx.