The aperture of a photographic lens is a hole that can be adjusted to different sizes, using the aperture ring. This ring is behind the lens, but in front of the shutter. The aperture ring is a flat circle with a small hole in the centre. The small hole is called the "aperture". The size of the aperture can be changed. When the aperture is very small only a small amount of light can enter the camera. When the aperture is big, a lot of light can get in.