Bob Atkins's Guide to Digital Camera Basics
If you have just bought your first digital camera and are wondering what some of the features actually do, then Bob Atkins’s guide to the basics is a great place to start learning.
“Sensitivity settings on digital cameras are the equivalent of ISO ratings on film. Just about every digital camera will have settings with a sensitivity equivalent to ISO 100 film and ISO 200 film. Many will have an ISO 400 setting, but above that the images from cameras with small sensors gets pretty noisy. The more expensive digital SLRs with much larger sensors have much higher sensitivity settings. At ISO 400 they are virtually noise free and some can go as high as ISO 3200 or even ISO 6400!”