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Aperture

What you should know about your camera's aperture


The aperture is the hole you see in the diaphragm of the lens.
The aperture is the hole you see in the diaphragm of the lens.

WHAT IS AN APERTURE?

An aperture - any aperture - is essentially a hole or an opening. Your mouth, for example, is an aperture. In a camera, however, an aperture is an opening in the lens' diaphragm.

This aperture wants some food put in it. This young crow may help you to remember that an aperture is an opening. (It's safe to say, in this case, that the aperture is wide open.)
This aperture wants some food put in it. This young crow may help you to remember that an aperture is an opening. (It's safe to say, in this case, that the aperture is wide open.)

The diaphragm mechanism of a lens acts like the iris of a human eye. In fact, some photographers refer to the diaphragm as the lens iris. The eye dilates (opens wider) and constricts (becomes narrower) because of the ability of the iris to adjust to more or less light. In photography, "aperture" describes not only the adjustable opening in the diaphragm, but the term also refers to the size of the opening.

WHAT DO YOU DO WITH AN APERTURE?

By varying the diameter of the aperture, you control the amount of light passing through the lens into the camera to expose the film or the sensor of a digital camera. A large aperture (or wide lens opening) lets in more light than a small one, and can deliver the same brightness from a dimly-lit subject as a small aperture will deliver from a brilliantly-lit subject.

Aperture works in conjunction with the shutter to determine the amount of light that reaches the film or digital sensor. It is one of a camera’s primary exposure controls, adjustable on all but the most basic cameras, whether manually by you or automatically by your camera if so designed.

HOW DOES IT WORK?

Most diaphragms are made from thin metal blades which overlap. By rotating an aperture control ring fitted around the barrel of the lens, the blades move smoothly towards the center of the lens or away from it, resulting in the aperture being reduced or enlarged in diameter.

HOW DO I KNOW WHAT MY APERTURE SETTING IS?

The size of the aperture (the degree to which the lens is said to be "open") is represented by numerically-identified ƒ-stops (pronounced "eff-stops"), which can typically be found engraved on the control ring. The aperture ring can be turned to select one or another ƒ-stop. You will feel a distinct click as each ƒ-stop is selected. (Some cameras require you to choose the aperture with a dial on the camera itself.)

The bottom row of numbers (16, 11, 8, etc.) on this lens shows the aperture settings of the lens, which is currently set at -5.6. The numbers are inscribed on an adjustable
The bottom row of numbers (16, 11, 8, etc.) on this lens shows the aperture settings of the lens, which is currently set at -5.6. The numbers are inscribed on an adjustable "aperture control ring."

Basic ƒ-stop numbers are 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64 and 90. Your lens' aperture ring will contain some, but not all, of these ƒ-stop index numbers in a series from the smallest to the largest. When written, these numbers usually appear as "ƒ-1.4, ƒ-2," and so on, even though the prefix "ƒ-" does not appear before the numbers on your aperture ring. (You will sometimes also see them written with a slash instead of a dash i.e. ƒ/1.4 or ƒ/2, or just with the letter “f” before the number, as in f 8.)

IF EACH ƒ-STOP IS A DIFFERENT APERTURE SIZE, WHAT DO THE ƒ-STOP NUMBERS MEAN?

It seems contradictory but is important for you to remember that a larger ƒ-stop number designates a smaller lens opening, and vice-versa. For example, an aperture of ƒ/22 is a very small lens opening, whereas an aperture of ƒ/1.4 is a relatively huge opening, and will let a great deal more light pass through the lens. The widest aperture of your camera’s “normal” or standard 50mm or 55mm lens may be ƒ/1.2, ƒ/1.4, ƒ/2 or ƒ/2.8, depending on make and model. All of these are relatively large openings.

An aperture of f16 is a small opening.
An aperture of f16 is a small opening.

A lens is said to be “fast” when it has a particularly large maximum aperture, so a 50mm lens that opens to ƒ/1.4 is “faster” than a 50mm lens that has a maximum opening of ƒ2.8.

You are said to “open” the lens when you go from a smaller aperture to a larger one, and a lens is “wide open” or at "full aperture" when its maximum aperture is selected. When you select any smaller aperture, you are said to be “stopping down” the lens, so a change in aperture from ƒ/5.6 to ƒ/11 involves stopping down two stops - i.e from ƒ/5.6 through ƒ/8 to ƒ/11. (It seems strange to be stopping down with ƒ- numbers that go up, but that’s the way it is.) A lens that is fully stopped down is at its minimum aperture.

An aperture of f/1.4 is a wide opening.
An aperture of f/1.4 is a wide opening.

IS THERE A REASON FOR THE PARTICULAR ƒ-STOP NUMBERS?

ƒ-stop numbers are based on a standard geometric scale. Each ƒ-stop is precisely engineered to let in twice as much light as the next smaller ƒ-stop, and half as much light as the next larger one. ƒ/8 therefore allows twice as much light through the lens as ƒ/11 and half as much as ƒ/5.6. This of course also means that ƒ/8 allows the passage of four times as much light as ƒ/16 which is two stops smaller, or eight times as much light as ƒ/22, which is three stops smaller.

WHAT IF I SET MY APERTURE BETWEEN TWO ƒ-STOPS?

Many cameras will function with the aperture set between two ƒ-stop numbers, and then your aperture is neither one nor the other, but becomes a setting between the two. (There will be no discernible click when you set your aperture between two marked ƒ-stops.) Many photographers refer to this as a half-stop, but they are being optimistic in assuming the aperture is set precisely halfway between two stops. (See Aperture Trivia for a complete list of stops and half-stops.)

OK, WHERE DO I GO FROM HERE?

As you wend your way through this section on aperture, you will be exposed to the ways in which your camera's aperture can be used to improve your photography. Ability to change the lens’ aperture settings is particularly important because the size of the lens opening not only works in direct partnership with your camera's shutter speed to provide correct exposure, but also governs increases or decreases in "depth of field".

DEPTH OF FIELD? WHAT'S THAT?

Understanding the concept of depth of field and putting it to work are crucial to your success as a photographer. It's all about how much of the scene you are photographing will or won't be in focus. The concept and its application are explained in our Depth of field section, which we strongly recommend you visit.

Once you have a solid grasp of depth of field, you will have enormously increased your ability to control your camera's aperture, which will result in your producing many enjoyable photographs, all the more so because you will have consciously made them look the way they do.

 
Further information...
Aperture guide
Aperture trivia
Depth of Field
Related topics...

Optimum aperture

Aperture settings for flash