Aperture is the opening of a diaphragm inside the lens that increases (more light) or decreases (less light) in size and an ƒ/stop is the ratio of the lens’ focal length to the diameter of the aperture. The size of the aperture or ƒ/stop controls the amount of light that passes through the lens to the image sensor. The aperture opening is referred to as aperture, ƒ/stop or ƒ/number. The aperture does not block light from reaching the sensor because it never closes all the way down.

The largest or widest opening of the diaphragm is refered to as maximum aperture. Maximum aperture allows the greatest amount of light to pass through the lens creating shallow Depth Of Field and the ability to use a faster shutter speed, e.g., ƒ/2.8 is a faster lens than ƒ/3.5.