Despite the best efforts of some avid post-capture sharpeners the focus point of most images is set at the point of capture. However, the Lytro Light Field Camera allows the focus point to be changed after the image is captured, so you switch from an object in the foreground being sharp to the background. The image refocuses before your eyes.

Lytro has managed to achieve this feat by fitting a microlens array in front of the Light Field Camera’s sensor to scatter light exiting the lens in different directions depending upon the angle at which it hit the array. This information is then used to calculate how the light would have responded if the lens was focused at a different distance.
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