ISO
ISO 100
Let's start with the most basic of properties: ISO
Always remember one thing: We are attempting to capture light.
ISO refers to the sensitivity to light, for either a roll of film or a digital sensor.
The lower an ISO value (25-200), the less sensitive the film/sensor is to light.
Low ISO values are not very sensitive, as such it's often the preferred choice for bright daylight conditions and for very long-exposures (waterfalls, traffic, surrealism, etc.).
Increasing the ISO value to 400 and up, makes the film/sensor more sensitive to light. This allows us to shoot hand-held in low-light conditions, but if we're outside in bright conditions, the increased sensitivity allows us to have very fast Shutter-Speeds, so we can freeze our subjects in place.
A side effect to ISO is the grain (film) or noise (digital) structure found in an image.
Low ISO values have a tight grain/noise structure, making it virtually unnoticeable. But as we increase to a higher ISO value, this structure starts loosening up, dramatically increasing its visibility.
Sometimes having visible grain/noise in a photograph is exactly what we want, while other times it's not.
Aesthetically speaking, analog film grain is far more pleasing to the eye than digital noise.
The photographs used in this example cover the ISO range of 100 to 12,800, and illustrate the impact of digital noise on an image.
The images were magnified to 400%, then cropped.
Notice how the noise is not really visible at ISO 100, 200 or even 400.
It's at ISO 800 that the digital noise starts to become visible and as I increased the sensitivity, it became more pronounced and distracting.
When we load a roll of film in a camera, we are locked into that ISO value for the entire roll, all 24 or 36 shots (btw, each shot is also called an exposure).
With digital cameras though, we can change the ISO value from one exposure to the next. We can be at ISO 100 for one exposure, then go to ISO 1000 for another
Certainly one of the biggest benefits to digital cameras by far.