The lens and the capture electronics are the two most critical pieces of a vision system. Skimp on either, and the results are sub-par. Going with a fixed glass lens often improves quality over a plastic lens, but an adjustable zoom lens provides more options without having to move the camera. This is handy in taking photographs, but it can be useful in a range of other imaging applications as well, including robotics.
Adding a built-in zoom lens to small cellphone cameras is a challenge because of the small size of the entire system and the motor. The large quantities involved in the cell-phone business have definitely reduced the cost, though there are alternatives.
The typical zoom lens has three lenses that must be adjusted to provide the proper optical alignment to focus the image on the capture device (see the figure). This design requires one or more stepper or servo motors for movement.
OPTICS OPTIONS An alternative to the moveable lens system is the OptiML Zoom fixed lens architecture from Tessera. The lens is designed to provide a distorted image that must be adjusted in software. It also provides additional information in the center of the imager where oversampling occurs. The conversion algorithm expands the center and compresses the borders based on the desired amount of magnification.
The approach can provide up to three times magnification without the loss of resolution normally provided by conventional digital zoom approaches that simply expands the existing pixels. This magnification matches the performance of most motorized systems for compact imaging devices at a fraction of the cost. The approach also provides better low-light performance with a small, fixed F-stop.
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