In
order to increase the light-gathering efficiency of a CCD camera, some CCD detectors
use a microlens array over the imaging detector to gather and focus more of the
incoming light onto the individual pixels.

Each photosite (picture element or "pixel") is surrounded by an opaque mask covering
the shift registers and circuitry necessary to read out the image signal gathered
by the camera. This means that some of the light falling on the detector lands on
the detector's mechanical structure rather than the light-gathering portion and
is lost. This is shown by the green arrows in the illustration.

The microlens system is an array of tiny clear plastic lenses placed over the CCD
detector so that a single miniature lens is situated over each pixel. These lenses
bend the incoming light rays so that the light that would normally be lost on the
CCD structure is directed instead towards the photosite, where it is recorded as
part of the image. These deflected rays are shown by the red lines in the illustration.
The microlens system markedly improves the light gathering efficiency of each pixel
by putting to use incoming light that would otherwise be wasted.