The focusing system includes two corrective lenses that minimize distortion. The diagram at right shows how that incoming starlight strikes the 2.5-meter primary mirror, bounces back and strikes the smaller secondary mirror, then is reflected back through a hole in the primary mirror. The light passes through the first correcting lens and then through the second lens on top of the camera. Images from the system appear in good focus from an area of sky equal to about 30 full moons. Making the two-dimensional image The inner sanctum of the Sky Survey telescope contains what may be the most complex camera ever built.
Scientists encase each column of five devices in a vacuum-sealed chamber.
In order to enhance sensitivity, liquid nitrogen cools each chamber to -80 degrees Celsius. Each CCD is made up of more than four million picture elements, which release electrons as light is absorbed. The electrons in turn are amplified into electronic signals that can be digitized, recorded on tape and ultimately fed into a computer. A night's observing will produce up to 200 gigabytes of data on a dozen tapes. Each of the five rows of CCDs receives the light through a different colored filter, so each row records the brightness of objects in a different color.