The CCD Mosaic
Image taken from http://www-dapnia.cea.fr/Phys/Sap/Activites/Projets/Megacam/Mosaique/mosaique.html
Forty CCD chips glow in this picture of the MegaCam mosaic. This image was taken with MegaCam exposed to a flat illumination source. Each chip behaves a little differently, even when receiving the same amount of light - astronomers compensate for this by taking a picture of "blank" sky and subtracting it from each of their real images.