Photographic lens focusing system and method which compensates for size of aperture

A focusing system for a lens comprising:

• a memory storing focus error data for at least two aperture values relating the focus at each of the at least two aperture values to the focus at the fully open aperture;
• a focus detector which detects a focused state of the lens using a portion of the incident light rays of the lens, said focus detector possessing a detection aperture;
• a first drive unit which calculates a first focus drive amount, which focuses the lens for a maximum aperture, based on focus error data, the magnitude of the detection aperture, and the focused state detected by said focus detection device, and drives the lens based on the first focus drive amount;
• a second drive unit which calculates a focus error between a first aperture and a second aperture based on the focus error data and drives the lens based on the focus error that is calculated;
• and
• a control unit which controls said first drive unit and said second drive unit, the control unit provides the aperture data of the first aperture and second aperture to said second drive unit to cause said second drive unit to operate.

A focusing apparatus for correcting a focus of a lens to compensate for differences in aperture, said focusing apparatus comprising:

• a focus detection device which outputs a focusing signal;
• a first drive unit which focuses the lens at maximum aperture;
• and
• a second drive unit which focuses the lens for use at an aperture smaller than the maximum aperture.

A camera comprising:

• a lens;
• an aperture adjustable to restrict the light passing through said lens;
• a focus adjustment unit to move the lens so as to focus said lens;
• a focus detection device to output the focus of said lens at a detection aperture;
• a memory unit to store focus correction data relating the focus of said lens at the maximum aperture to the focus at each of a plurality of stopped-down apertures;
• a first drive unit which focuses said lens for use at the maximum aperture based on the output of said focus detection device and the focus correction data;
• and
• a second drive unit which focuses said lens for use at a stopped-down aperture based on the focus correction data.

A method of focusing a lens comprising:

• detecting focus of a lens at a detection aperture;
• retrieving focus connection data indicating an amount to correct the focus of the lens to focus at a maximum aperture based on the detected focus of the lens;
• and
• focusing the lens for a maximum aperture based on the detected focus and the retrieved focus correction data.