Digital Cameras
Digital cameras are used during investigations to help document the event. They are also used because of the visual anomalies that appear when taking photographs. The reason that is used to help explain why these visual anomalies appear in photographs but not to the human eye has to do with vibration or motion speed.
To explain why your eye may not see a ghost is illustrated by how a box fan blades appear when the unit is powered on. When it is powered off, you can see the blades. But as soon as the blades of the fan start to spin, their speed affords them a transparent quality your eye can not follow.
However, if you take a picture of the fan blades spinning, the shutter speed on the camera "blinks" faster than the reflection of visible light energy, capturing the individual blades. It is believed that ghosts show up in the same way in photographs.
