How it works: the liquid lens

If you’ve been paying attention (“The end of focus problems”, 6/14/09 and “Autofocus – Microscan got there first”, 6/22/09) ) you know that both Cognex and Microscan have launched code reading devices with liquid lenses. This allows them to focus on the target almost regardless of its distance from the sensor. In contrast, our regular machine vision lenses are completely dumb, only able to keep the image in focus over a small distance.

It’s a very clever way of mimicking the human eye and you might be wondering how it’s done. Well both Cognex and Microscan use technology from Varioptic, but I’ve just been reading about some researchers in Japan who’ve come up with another method.

They give details in “A rapidly deformable liquid lens” published on the SPIE web site December 14th, 2009. This makes for interesting reading, but for the really good stuff you need to scroll down to the end of the paper and click the video link. This shows the lens in operation, focusing and refocusing over a range of some 11mm.

Now I’m wondering, and perhaps some of you are ahead of me, could this work in reverse? In other words, could we measure height from the extent to which the lens has to be refocused?

I’ve a feeling that someone has already thought of this, but if not, add my name to the patent application!