Digital Cameras VS Film Sensitivity

The discovery of the effect of light on different substances and there application to register images goes back to the XIX century. The progress from the first experiments to the present day has been very fast and fruitful. The first photographic images were one of a kind and took hours to be registered. Soon the negative appeared, or first record from which you can obtain an unlimited amount of positive copies.

Even with the excellent quality of current materials, film is still something that depends on certain requirements in order for it to work, the most important thing is the amount of light the film is going to receive, so that after it is processed there will be an acceptable image. The amount of light the film receives during an exposure depends on the brightness of the scene and how we adjust the controls of the camera. For every film there is a exposure level so weak that it doesn't cause an effect (underexposed), a level in which the bright areas o the scene are registered with different tones (correct exposure), and a level above were the tones are compressed together (overexposure).

One first large difference between the eye and photographic film: while in your eye darkness and brightness are directly associated with existing light, in film dark without detail (transparent in the negative) means underexposure, and brightness (dark in the negative) means overexposure. A mistake in the exposure can make a sunny day spooky and the light of a candle blinding, because the exposure level is controlled with the camera.

Sensibility
The level which gives us a correct exposure with a determined film is defined by it's sensibility. It is said that a film is very sensitive when a low exposure level is required (a little bit of light for an acceptable image) and not sensitive when it needs a high exposure level (a much longer exposure for and adequate image). This information is considered by the photometer and easily allows us to achieve a correct exposure.

Digital Sensors
Television and the recording of animated images on magnetic support is the origin of digital photography . The photosensitive element in today's digital cameras descend directly from television and video cameras. In both cases light is captured by the lens and projected on an electronic sensor, which is a matrix of photosensitive receptors. The light which comes in contact with each point causes a weak electrical response, which is then amplified and turned into information. As with film, the exposure level determines the quality of the obtained image.