Digital senors and film are rated by the International Standards Organization (ISO) according to their relative sensitivity to light. We used to call this sensitivity “film speed” or “ASA” (American Standards Association), and it is still expressed as a number, with lower numbers indicating less sensitivity to light.
ISO/ASA 100 200 400 800 1600 3200
ISO, or film speed, is a setting to determine how quickly an image will be captured by either the film or digital sensor. The higher the ISO, the quicker the image will be captured and the less light that is required. The lower the ISO, the longer it takes for the image to be captured and the more light you will need.
ISO depends on your surroundings and the amount of light available.
It’s a good rule of thumb for digital cameras in general, to use:
100/200 outdoors, bright light
400 in the shade, overcast outdoors, inside with lots of light
800/1600 indoors, low-light conditions, sports or action.
The lower the film speed, the lower the digital noise (or film grain) and the higher the contrast. The higher you’re ISO, the more digital noise is created in the image and the lower the apparent contrast.
Now see that wasn’t so hard. If you ever have any questions please ask in the comment box below.