The aperture is actually the diameter of the hole inside the lens. Light enters the lens through an aperture. The smaller the aperture, the lesser light is allowed to get in and vice versa. It has an effect on the depth of field of the picture. The f/number gets lower as the aperture widens and more light enters into the camera. It is desirable in low light conditions, but it makes the depth of field shallow. It is not ideal when capturing landscapes. Exposure is much easier if you memorize the following f/stop scale: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 Wider the aperture, shallow will be the depth of field and vice versa.