The single most important aspect of photography is exposure (the amount of light reaching your camera’s sensor when you take a picture). Exposure is adjusted by three things: ISO, Shutter Speed and Aperture. ISO numbers measure how sensitive the camera is to light. Lower ISO (100, 200, 400) mean the camera sensor is less sensitive to light. The images are also less grainy and noisy. Higher ISO (800, 1600+) mean the camera sensor is more sensitive to light. Images then to have more grain and noise with higher ISO. Aperture controls how much light enters the camera through the lens. The more open your aperture, the less depth of field. The more closed your aperture the more depth of field. Open apertures means lower f-stop number (f/2.0, f/2.8, f/3.5). Closed aperture means higher f-stop number (f/11, f/16, f/22). Shutter speed controls how long the light entering the aperture exposes the sensor. The faster the shutter speed the sharper the image. Generally you can handhold the camera when your shutter speed is 1/focal length. Shooting at a slower shutter speeds requires a stiff hand or a tripod. Examples of shutter speed: Low (1/20, 1/50) and Fast (1/125, 1/500, 1/1000).