ISO 100

ISO 100

We begin with the most fundamental property: ISO

ISO refers to the sensitivity to light for either a roll of film or a digital sensor. 

The lower the ISO number (25-200), the less sensitive the film/sensor is to light. Low ISO values are often the preferred choice for bright daylight conditions and for very long-exposures. 

With an ISO of 400 and up, the film/sensor's sensitivity to light increases.

This allows us to shoot hand-held in low-light conditions, and if we're outside in bright conditions, this increased sensitivity allows us to have very fast Shutter-Speeds, so we can  freeze our subjects in action.

(A camera's automatic "Sports" mode sets a high ISO value for us.)

A side effect to ISO is the grain (film) or noise (digital) found in an image. Low ISO values have a tight grain/noise structure, making it virtually unnoticeable. As we increase to a higher ISO, this structure starts loosening up, dramatically increasing its visibility.

Sometimes this 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 increase sensitivity, it became even 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 from one image to the next. We can be at ISO 100 for one exposure, and ISO 12,800 for another, all depending on what the camera is capable of.

Certainly one of the biggest benefits to digital cameras by far.

"Since I’m inarticulate, I express myself with images."

Helen Levitt

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