Charge conservation and CCD aperture photometry

The Lick Observatoryʹs CCD controller is a new type controller. It has the ability to exchange MPP (Multi-pinned phase) mode and normal operation within one CCD system. There are at least 4 CCD cameras using this type of controller in China since 2002. The weakness of this controller is that blooming occurs before nonlinearity and long before saturation. However, although it is no good for observation of bright extended sources and for constructing the point spread function from observing bright stars, aperture photometry of bright point sources (stars) is still feasible due to the principle of charge conservation. This point is confirmed in this paper.