The ability to focus is becoming a high-priority feature in compact cameras for biometric, medical, and industrial applications. It lets users capture images over a greater depth of field, thus making it easier to position the eye in front of a biometric ID or samples for a medical-diagnostic camera. Focusing would also let machine-vision systems work on parts without regard to their exact distance from the camera or whether the parts have significant depth.
Several camera makers use the miniature M3-F focus module from New Scale Technologies, Victor, N. Y., to move traditional lenses with high resolution, repeatability, and accuracy, and let the camera autofocus on anything from 1 in. away to infinity in most cases. Position control on the lens has a 0.5-micron resolution.
The single-lens module works with glass or polymer lenses ranging up to M12 and weighing up to 5 gm. Compatible lenses include the DSL935 M12 lens from Sunex Inc., Carlsbad, Calif., which are said to deliver transmission and clarity superior to liquid-lens devices. The module measures approximately 20 × 22 × 16 mm, about the same size as a fixed lens holder, and does not add to the total track length (TTL). An embedded closed-loop drive uses little power (3.1 to 3.6 V) and keeps module size and external processing requirements to a minimum. The 5.8-gm module accepts high-level commands over standard serial interfaces (12C or SPI). As a closed-loop system, the M3-F has no hysteresis and exhibits high accuracy and repeatability independent of temperature. The module also holds focus when power is switched off.