Sensor Sensitivity or ISO

The last piece in the exposure puzzle is sensitivity or ISO. This is the light gathering potential of the sensor. The higher the ISO set on the camera the less light needed to activate it allowing us to shoot in darker locations or allowing faster shutter speeds. The base ISO is usually 100 or 200, although some cameras will go as low as ISO 50. The sensitivities can be increased to 400, 800, or even 6400 on high-end digital SLRs. When increasing the sensitivity, the output of the sensor is amplified, so less light is needed. Unfortunately that also amplifies the undesired noise. This creates more noise in our images similar to larger grain when shooting faster speed film. It is similar to turning up the volume of a poor quality audio cassette recording. Doing so will not only amplify the music but also the hiss and crackle or background "noise". Improvements in sensor technology are steadily reducing the noise levels at higher ISOs, especially on higher-end cameras. And unlike conventional film cameras which require a change of film roll or the use of multiple bodies, digital cameras allow you to instantly and conveniently change the sensitivity depending on the circumstances.