One of the major difference between a consumer digital camera and a digital Single Lens Reflex (DSLR) is that the former produces images with a lot of noise when using high ISOs and long exposure times, and the latter is practically noise-free (though high ISO performance varies depending on camera manufacturer and model). Noise is apparent by the presence of color speckles where there should be none. For example, instead of a blue sky, you notice faint pink, purple and other color speckles amongst the otherwise blue sky.
The exposure is the combined factors of how long time the sensor is exposed to light, how much light comes through and how sensitive the sensor is to light. It’s based on three things, Aperture size, Shutter speed and ISO.
In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.
Camera Noise or Grain refers to the amount of distortion to your images that is caused as a result of using certain ISO / ASA settings. It can also be the result of enlarging images bigger than the tolerance of the film or digital settings within your camera will allow.
Would you like to learn how to avoid Noise? Keep close! ;)