ISO

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 it is to light. Low ISO's are often the preferred choice for bright (daylight) conditions and long-exposures. 

With an ISO of 400 or more, the sensitivity to light increases. This allows us to shoot hand-held in low-light conditions. If we're outside in bright conditions, this increased sensitivity allows us to use very fast Shutter-Speeds, allowing us to freeze our subject in action.

A camera's automatic "Sports" mode sets a higher 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 visibility.

Sometimes, grain/noise in the photograph is exactly  what we want, other times it's not.

Aesthetically speaking, analog film grain is pleasing to the eye, while digital noise is not.

The photographs used in this example cover the ISO range of 100 to 12,800.

The images were magnified to 400%, then cropped to really  show the impact of the noise.

Notice how the noise is not really visible at ISO 100, 200 or even 400.

It's at ISO 800 and beyond, that it starts to become visible and as we increase the sensitivity, it becomes even more pronounced.

When I start the process to determine my exposure, ISO is the first property I set.

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

Helen Levitt

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