Sensitivity
Along with aperture and shutter speed, sensitivity is the third parameter that controls the exposure triangle.
In film photography, sensitivity relates to a chemical property of the film, which controls the relative reaction of the film to a certain quantity of light. The sensitivity is measured in ISO. The higher the ISO reading, the less light needed to achieve a specific exposure.
In digital photography, the same concept applies. Except here sensitivity can be changed from one shot to the next, while in film sensitivity is inherent to the film, and thus can only be changed by changing film (although there are ways to “push” sensitivity to some extent).
As with aperture and shutter speed, sensitivity has another impact than just the exposure triangle. However, in this case, and except for some very specific situations, we can say that you should always set the lowest sensitivity possible (usually 100ISO on digital cameras). In fact, increasing sensitivity beyond a certain point may create grain (both on film and digital) and/or noise (digital).
In film photography, sensitivity relates to a chemical property of the film, which controls the relative reaction of the film to a certain quantity of light. The sensitivity is measured in ISO. The higher the ISO reading, the less light needed to achieve a specific exposure.
In digital photography, the same concept applies. Except here sensitivity can be changed from one shot to the next, while in film sensitivity is inherent to the film, and thus can only be changed by changing film (although there are ways to “push” sensitivity to some extent).
As with aperture and shutter speed, sensitivity has another impact than just the exposure triangle. However, in this case, and except for some very specific situations, we can say that you should always set the lowest sensitivity possible (usually 100ISO on digital cameras). In fact, increasing sensitivity beyond a certain point may create grain (both on film and digital) and/or noise (digital).
How
a digital camera behaves at high iso settings depends on the quality
and the size of the sensor. Most SLR cameras have half frame (half the
size of a 35mm film) or full frame (size of a 35mm film) sensors, which
allows them to go to quite high iso settings with very little noise.
They also have sophisticated built-in software to reduce noise.
Point&Shoot cameras usually have smaller sensors, and thus are more
limited in terms of iso settings.