The camera has a sensor that records the image, and the more light that this sensor records at once, the brighter the image. The amount of light it picks up is measured in ISO. The higher the ISO number, the brighter the image and the more grain the image will have. A D.S.L.R. has a scale for setting like ISO. The camera can often go halfway up the scale before it becomes to granny to use professionally. The exact place in the scale is depicted on the camera. The other two ways to control the exposure (brightness) are F-Stop and Shutter speed.