ISO rating for Film Speed
Taken with a Nikon D50 and AF Zoom-Nikkor 70-300mm f/4-5.6G lens
ISO stands for 'International Organization for Standardization' and their film speed ratings are used to indicate the relative amount of light necessary to give a proper exposure. A normal film will be rated at ISO 100. A film rated at ISO 200 will give a proper exposure with only half the amount of light compared to the ISO 100 film, enabling you to shoot in lower light or with a smaller aperture or faster shutter speed. The ISO 200 film would be referred to as a 'faster' film. There are films available that range in speed from ISO 25 to ISO 1600.
So why not use the faster films all the time, what are the advantages of slower films?
The faster films have a more prominent grain structure the individual grains clump together to form spots that are visible to the naked eye, especially when you blow the photo up to A4 or larger from a 35mm negative. In certain circumstances this effect can be used creatively especially in black and white photography but mostly it is undesirable.
How does all this effect digital cameras?
In the digital photography world the phenomenon is called 'noise' not 'grain', the cause of the problem is slightly different. When light levels are low, the sensor has trouble reading the scene properly and pixels of random colour are thrown into the picture. However to us photographers the end result is the same or very similar.
Labels: AF Zoom-Nikkor 70-300mm f/4-5.6G, Nikon D50, Photography
