Steered sum low cost auto focus system

Apparatus for use with an auto focus system which includes first and second pairs of radiation responsive detectors positioned with respect to moveable lens means to receive radiation therethrough from a remote object to be focused upon, each detector operable to produce an output signal indicative of the radiation received thereby and motive means operable to move the lens means from a first position on one side of the proper focus position to a second position on the other side of the proper focus position, the apparatus comprising:

• first signal processing means connected to the first pair of detectors and operable to produce a first signal indicative of a function of the output signals from the first pair of detectors, the function producing a first curve as the lens means moves from the first position to the second position crossing a reference axis proximate the proper focus position;
• second signal processing means connected to the second pair of detectors and operable to produce a second signal indicative of a function of the output signals from the second pair of detectors, the function producing a second curve as the lens means moves from the first position to the second position crossing the reference axis proximate the proper focus position;
• third signal processing means connected to said first and said second signal processing means and operable to produce a sum signal indicative of the sum of the first and second signals, the sum signal having a first characteristic when the lens is on one side of the proper focus position and a second characteristic when the lens is on the other side of the proper focus position;
• fourth signal processing means connected to said first and second signal processing means and operable to produce a difference signal indicative of the difference between the first and second signals, the difference signal having a first characteristic when the lens is on one side of the proper focus position and a second characteristic when the lens is on the other side of the proper focus position;
• signal comparing means connected to said third and said fourth signal processing means and operable to transmit the sum signal when the magnitude of the sum signal is greater than the magnitude of the difference signal and to transmit the difference signal when the magnitude of the difference signal is greater than the magnitude of the sum signal;
• and
• means connected to said signal comparing means and to said motive means and responsive to the signal transmitted by said signal comparing means to stop the motive means from further moving the lens when the transmitted signal changes characteristic.

Range determining apparatus comprising:

• lens means;
• motive means connected to move said lens means to a proper focus position with respect to a remote object, the proper focus position being indicative of the range to the remote object;
• first and second radiation responsive detectors mounted to receive radiation from the remote object through said lens means and operable to produce output signals a.sub.1 and b.sub.1 indicative of the radiation received thereby, a.sub.1 being substantially equal to b.sub.1 when said lens means is proximate the proper focus position;
• third and fourth radiation responsive detectors mounted to receive radiation from the remote object through said lens means and operable to produce output signals a.sub.2 and b.sub.2 indicative of the radiation received thereby, a.sub.2 being substantially equal to b.sub.2 when said lens means is proximate the proper focus position;
• first signal combining means connected to said first and second radiation responsive detectors to receive the output signals and to produce a first combined signal generated by a combination of a.sub.1 and b.sub.1 as said lens means moves;
• second signal combining means connected to said third and fourth radiation responsive detectors to receive the output signals and to produce a second combined signal generated by a combination of a.sub.2 and b.sub.2 as said lens means moves;
• sum means connected to said first and second signal combining means to receive the first and second combined signals and operable to produce a sum signal representative of the sum of the first and second combined signals, the sum signal having a first slope and having a predetermined value when said lens means is at a proper focus position;
• difference means connected to said first and second signal combining means to receive the first and second combined signals and operable to produce a difference signal indicative of the difference between the first and second combined signals, the difference signal having a second slope and having a predetermined value when said lens means is at the proper focus position;
• comparing means connected to said sum means and said difference means to receive the sum and difference signals and to compare the magnitude of the first slope with the magnitude of the second slope, said comparing means operable to transmit to an output that signal having the greater slope;
• and
• resultant means connected to the output of said comparing means to receive the signal having the greatest slope and operable to produce a resultant signal when the signal having the greatest slope reaches the predetermined value.