Exposure...Part 3 - ISO

ISO - Sensor Sensitivity to Light ISO stands for the "International Organisation for Standardization". The ISO was founded in early 1947 and is headquartered in Geneva, Switzerland and is composed of representatives from various of it's 158 members national standards organisations.

One of the standards defined by this organization is photographic film's sensitivity to light. An image sensors 'film speed', is often referred to as its "ISO number."

ISO - and Stops of Exposure

Just like aperture and shutter speed ISO is set up as multiples of 2. ISO 100 allows twice as much light as