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Optimising Motorised Lens, P-iris and Liquid Lenses

Self-contained machine vision systems are becoming increasingly common and have generated a requirement for miniature board-level lens controllers to be embedded into small enclosures. Mechanically motorized lenses and the new electrically-tunable liquid lenses are beneficial in many applications where it is difficult to access the lens, or very rapid adjustments are needed.

Intelligent Lens Control

Many factors can affect light levels reaching the camera in both indoor and outdoor applications. For example, in surveillance and Intelligent Traffic Solutions variations in light levels can change with weather conditions and the time of day. In industrial inspection applications light levels may vary due to changes in inspection speed or the reflectivity of the objects being inspected. For most applications, if the intensity of the light itself is not being controlled the size of the aperture in the lens iris can be used to regulate the intensity of light reaching the camera sensor.

When the camera and lens are often located in inaccessible positions, for example in in a confined space on a production line or on a motorway gantry, the iris adjustment needs to be motorized. An approach known as P-iris (Precise-iris) is often the preferred solution, especially where image capture is triggered externally as on production lines. P-Iris uses a stepper motor to drive the aperture to an exact ‘F-number’ position which optimizes the optical performance of the lens. Motorized lenses can also provide zoom adjustment as well as iris control. Zoom is needed in applications such surveillance, sports and traffic monitoring, especially in long distance monitoring such as port or border surveillance in order to show objects or people of interest at higher magnification.

While motorized lenses can be used to adjust focus over a range of distances, electrically-tunable liquid lenses provide an impressive alternative. Gardasoft liquid lens controllers can drive the lens to an accurate focus position in less than 10ms which is far faster than is possible with a motorized lens. In ITS and ANPR or tolling applications, the distance from vehicle to camera can vary significantly and quickly. For conveyor belt inspections with products of different sizes or varying distances from the camera, refocusing is needed at production line speeds. By using a liquid lens the precise focus of each object is achieved and the iris adjustment can be permanently set to give good quality images.

Gardasoft has extensive experience in developing embedded controllers for motorized lenses for many applications. The CL190/CL191 single-channel lens controllers offer an embedded solution for liquid lens control and are available as a miniature PCB version or as a design module to be added to the system design file. A miniature lighting control board is also available.