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Crude contraptions using mirrors to see round corners have been used for centuries as spying devices, as well as at war.

But now scientists have developed a camera system that lets users see round corners using laser light.

By tracking diffusely reflected light, the invention reconstructs the shape of objects outside of the field of view.

Lights, camera, action! Computer scientists have developed a camera system (pictured) that that lets users see round corners without using a mirror. Using diffusely reflected light from a laser, it reconstructs the shape of objects outside of the field of view

Researchers at the University of Bonn and the University of British Columbia in Vancouver, came up with the array of devices.

A laser is shone on a surface, such as a wall, and serves as a source of scattered light, as well as the source of information.

In a demonstration, a laser is shown shining on a white wall, while a camera watches the scene. All it can see initially through the lens is a 'spot' of light.

A computer records the image and the data is processed so the outlines of an object gradually appear on a screen - but it is behind a partition, proving that the camera can see round corners.

Matthias Hullin, of the University of Bonn, explained: 'This is an actual reconstruction from diffusely scattered light. Our camera, combined with a mathematical procedure, enables us to virtually transform this wall into a mirror.'

This graphic shows the set-up of the equipment. The light source (red) and camera (field of view marked in blue) both look at a white wall. The objects the experts want to reconstruct (green box) are hidden and are only accessible through indirect reflections off the diffuse wall

The laser 'dot' on the wall is a source of scattered light, some of which falls back onto the wall and into the camera.

'We are recording a kind of light echo, that is, time-resolved data, from which we can reconstruct the object,' he said.

'Part of the light has also come into contact with the unknown object and it thus brings valuable information with it about its shape and appearance.'

To be able to measure such echoes, a special camera system is required, which the team developed.

In a demonstration, a laser was shown shining on a white wall, while a camera watched the scene. All it could see initially through the lens was a 'spot' of light. These large cardboard letters were hidden out of the cameras' field of view in the experiment

The computer recorded the image and the data was processed so the outlines of the hidden object gradually appeared on a screen, proving that the camera can see round corners. The reconstruction of the cardboard letters is shown

Unlike conventional cameras, it records not just the direction from which the light is coming, but also how long it took the light to get from the source to the camera.

This technology is nothing new in itself, as such image sensors are found in depth image cameras used in video game controllers.

The scientists said the challenge was extracting the information needed from time-of-flight measurements.

Professor Hullin compared the situation to a room which reverberates so greatly that someone can no longer have a conversation with another person.

The new camera system lets people see round corners without using a mirror, like a traditional periscope (pictured)

'In principle, we are measuring nothing other than the sum of numerous light reflections which reached the camera through many different paths and which are superimposed on each other on the image sensor,' he said.

This problem, known as multipath interference, has been baffling engineers for a long time.

Traditionally, they would attempt to remove the undesired multipath scatter and only use the direct portion of the signal.

Based on an advanced mathematical model, the computer scientists developed a method that can obtain the desired information exclusively from what would usually be considered noise rather than signal. 

Since multipath light also originates from objects which are not at all in the field of view, the researchers can make visible what is virtually invisible.

'The accuracy of our method has its limits, of course,' Professor Hullin admitted, as images of what is around a corner are only shown as rough outlines.

But the scientists hope that higher resolution images will be possible soon.

They will  report on their research at the international Conference for Computer Vision and Pattern Recognition (CVPR) taking place next week in Columbus, Ohio.