Automatic focus system with loss of correlation inhibit

In a continuous automatic focusing system of the spatial correlation type, in which the position of primary optical means is controlled in accordance with a time varying correlation signal the magnitude of variation of which changes with different illuminations, different contrasts and different scene compositions, the improvement comprising:

• inhibit means for inhibiting, in the event of loss of a suitable correlation signal, movement of the primary optical means from a position determined by the last suitable correlation signal.

Apparatus for use with an auto focus system which has a primary optical member to be positioned at a desired position so as to provide a focused image of an object which is within a field of view, radiation responsive means operable to produce radiation signals which vary with the intensity of radiation received thereby, scanning means operable to transmit radiation from the field of view to the radiation responsive means, signal processing circuitry connected to the radiation responsive means to receive the radiation signals and operable to produce a correlation signal which varies with the operation of the scanning means and normally containing a major extrema indicative of the range to the object, the correlation signal also containing variations the magnitude of which changes the radiation intensity and contrast in the field of view, and positioning means connected to receive the correlation signal and to move the primary optical member toward the desired position, comprising:

• inhibit means connected to receive the correlation signal and to produce an output signal whenever the variations in the correlation signal are below a predetermined level, and
• means connecting said inhibit means to the positioning means to inhibit movement of the primary optical member upon the occurrence of the output signal.