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The original Surface tables are one of the chief attractions here at PDC, with attendees clambering to get their hands on the dozen or so tables dotted around the conference halls.

However, the highlight of today's keynote from Microsoft Research was a demonstration of a new Surface prototype called SecondLight, which is being developed at the company's labs in Cambridge.

The new table projects an image through the table itself, so that any translucent material (such as tracing paper or perspex) held above the Surface screen displays a different image to what you see on the table's display.

This means you can have a satellite image of a town on the table, and have the street names projected on to a piece of paper that the user holds above the map. Or you could have a photo of a car, with the tracing paper displaying images of its innards as you pan the paper across the screen. Microsoft described the technology as a "magic lens".

Click here to see a video of SecondLight in action (Windows Media

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download).

How it works

SecondLight works by projecting two different images from beneath the table. The table surface itself is formed of a liquid crystal display that switches between frosted and transparent states when electrical voltage is passed through it.

By rapidly flicking the screen between the two states, the table appears as permanently diffuse, displaying an image like an ordinary Surface table.

The screen is, in fact, transparent for half the time. And during these periods then second image is beamed on to the paper, confusing the eye into believing it's seeing two images simultaneously.

Using an infrared camera, the secondary "display" can also be used as a multitouch surface. What's more, it can display video.

Microsoft gave no indication of when SecondLight will be ready for commercial release, but judging by the interest in the ordinary Surface tables, it shouldn't keep this one locked in the labs for long.

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