f-Stop aka Aperture

Apertures: The aperture is simply the size of the opening that lets light through the lens.

The number for the aperture that you will set is called an f-stop. It is a fraction that relates to the actual size of the lens opening. For the rest of this course, aperture refers to the size of the opening in the lens, while f-stop is number that you set. The number represents a fraction and is displayed like this: f/2 or f8. It translates into a fraction by replacing the f with a 1 and now we see these f/stops actually refer to 1/2 and 1/8.

OKAY get ready for it to go a little deeper.

Since we can put different lenses on our cameras (or select different focal lengths on a zoom lens) it is necessary to express the actual size of the aperture opening in relative terms; thus f/2 instead of 1/2. To take this further, if you had a 50mm lens on your camera and you set your aperture to f2, you would be setting an aperture diameter of 25mm (1/2 of 50mm = 25mm).

If you selected f/2 on a 100mm lens that opening would be 50mm in diameter (1/2 of 100mm = 50mm). f/2 on a 300mm telephoto lens would have aperture with a 150mm diameter, and so on. Because the f-stop should be considered a fraction, i.e. f8 can be considered 1/8 and f2 is 1/2, we can better understand why f2 is a larger opening than f8; because 1/2 is larger than 1/8.

Viewing the Aperture Diagram we see that when the aperture gets smaller and lets in less light, the f-stop number gets larger. F8 is a larger number than f2 yet the aperture is smaller and lets in less light. When you convert the f-stops to fractions, it makes more sense, 1/8 is smaller than 1/2, hence f8 lets in less light.

Apertures range in f-stops from f1 to f64 in one-stop increments. A one-stop increment either doubles or halves the amount of light hitting the film. The whole f-stop numbers are listed below. You will be responsible for committing these whole f-stops to memory.

1 _ 1.4 _ 2.0 _ 2.8_ 4.0 _ 5.6_ 8.0 _ 11 _ 16 _ 22 _ 32 _ 45 _ 64

Full stop adjustments of the these variables will allow either twice as much (2x) light, or half (½) as much light to the film plane.