1. A method of determining a focus position of a lens structure relative to an imaging sensor, the method comprising: dividing a scene imaged by the sensor into zones that each comprise a plurality of pixels; reading a plurality of sharpness values for each zone, each of the plurality of sharpness values corresponding to one of a plurality of predetermined lens positions; determining a zone weight for each zone, the zone weight for each zone determined with reference to the scene; and using the plurality of sharpness values and the zone weights for each zone to determine a focus position for the lens.