Understanding “Aperture”

Last modified on 2011-09-21 01:40:53 GMT. 5 comments. Top.

Understanding Aperture
Every camera lens has a piece of glass on the front that covers a hole in the lens that lets light into the body of the camera. In the barrel of the lens is a set of blades that make that hole larger or smaller. The size of that hole is called the aperture. The smaller the hole the less light comes through at once. The larger the hole the more light comes through. It’s like turning on your water faucet at home. If you turn it just a little a small amount of water comes out at once. If you turn it all the way a lot of water comes out at once. This is the aperture setting.

The size of the aperture is designated by numbers called f stop settings. Usually those numbers will be settings in the range somewhere between 1.4 to 32. The smaller the number the larger the aperture. As the f stop number increases the aperture decreases. (The reason for this is a mathematical explanation which is very complicated and is different for every type of lens. It has something to do with lens size and its proportions. The explanation is not relevant to this article.)

The picture below illustrates the relationship between aperture size and f stop number. The f/1.4 setting shows that it is a much larger hole than f/16.

Photography Aperture

Apertures from f/1.4 to f/16

Aperture is measured in a scale called “stops.” Here is a scale of full stop increments for a very fast lens that has an f/stop rating of 1.4. Many lenses will start with 4.0 or less.

• 1.4
• 2.0
• 2.8
• 4.0
• 5.6
• 8.0
• 11
• 16
• 22

Many camera have settings at 1/2 stops and even 1/3 stops in between each of the setting above but to keep things simple I’ll not cover that chart in this article.

Most of our electronically controlled cameras will automatically detect the f/stop limits of the lens installed.

Two Important Reasons for controlling Aperture Size

• Number One: It allows control of the volume of light that comes into the camera at one time. When your subject is bright you need to use a smaller aperture setting (larger numbers – f/8, f/11, f/16, f/22). When the light on your subject gets dim you will need to set a larger aperture (smaller numbers – f/5.6, f/4, f/2.8).

• Number Two: Aperture settings control another very important element in photography called “depth of field.” “Depth of field” is the term used to describe how much of your photograph will be in focus. Here is how it works. The smaller the aperture (the hole in the lens) the greater the depth of field. That means that f/16 or f/22 will provide a photograph that has almost everything in focus from the foreground to the background. An aperture setting of f/1.4 or f/2.8 will cause some portion of your photograph to be out of focus. There are times when this is very advantageous, for instance if the background is distracting it is a good time to use a large aperture, focus on your subject and let the background be out of focus.

Here is an illustration of using a larger aperture to blur the background that would otherwise have been very distracting if a small aperture had been used:

Aperture f/1.4

Aperture f/14

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