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The latest advance in color machine vision is the use of liquid lenses, which make focusing automatic from just inches to infinity.
IVA Corp. (Sudbury, Mass.) has developed a 2mp color camera with a Varioptic (Lyon, France) liquid lens that allows complete real-time dynamic control over focus during operation with supplied software or while in auto focus. The USB camera is being followed up with an Ethernet version, the IVIN™2M-ETH, which features a CMOS imager with selectable display resolution up to 1600 x 1200, incorporating a progressive scan sensor with an electronic rolling shutter.
"It has a great advantage for certain applications," says Dave Birkner, President of IVA. "The lens has no moving parts. It's just an oil/water interface between a couple of pieces of glass. The junction forms a semispherical meniscus that can be varied with high-voltage AC current. It's high voltage, but low current so it doesn't take much power to run. It's very fast. It's practical to have the camera focus on different things and still achieve a sharp image."
The liquid lens was originally designed for cell phones, Birkner explains. "It generated enough interest that we wanted to use it for anything, not just hard-wired for specific applications. That prompted the USB device."
Basically, a water drop is deposited on a metal substrate covered by a thin insulating layer. A voltage applied to the substrate modifies the contact angle of the liquid drop. The lens uses two isodensity liquids; one is an insulator, the other a conductor. The variation of voltage leads to a change of curvature of the liquid-liquid interface, which in turn leads to a change in the lens' focal length. The lens looks a fraction away and focuses automatically from there to infinity.