These charges can then be measured and converted into digital numbers that indicate how much light hit each site. Courtesy of IBM . Just as in a traditional camera, light enters a digital camera through a lens. A timing circuit tells it when to start and stop the exposure Electromechanical shutters are mechanical devices that are controlled electronically. Electro-optical shutters are electronically driven devices in front of the image sensor which change the optical path transmittance.
Image sensors are often tiny devices.
The three most common sizes used in digital still cameras are just a fraction of the size of a 35mm slide or negative. From Light to Images When the shutter opens, the lens focuses the scene on the sensor. Some photosites on the image sensor record highlights, some shadows, and others record all of the levels of brightness in between. Each site converts the light falling on it into an electrical charge. A photosite in a highlight area will have a much higher charge than one in a shadow area.