A camera is basically a light tight box, and in order to expose an image, there must be a way of letting in a controlled amount of light.
An aperture is simply a hole that lets in light.
A six-blade iris from a camera lens
Adjusting the size of the aperture controls the amount of light that enters the camera during exposure.
The size of the aperture opening is measured in f-stops.
Starting with f/1.0 we have a series of numbers that represent full stops.
These full f-stops, from larger to smaller, are as follows:
f/: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32, 45, etc.
It is often confusing at first to get used to the larger numbers representing a smaller opening. In the illustrations below you can see how the size of the aperture gets smaller as the number of the f-stop gets larger.
Each full f-stop lets in exactly 1/2 the amount of light as the previous stop, and twice the amount as the next stop. So f/5.6 lets in 1/2 as much light as f/4, and twice as much as f/8.
Shutter speeds are also set up this way as will be explained in the camera shutter speeds lecture.
In addition to controlling exposure, f-stops also affect depth of field. The smaller the f-stop you use, the more depth of field you get. For more on Depth of Field click HERE.
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Here’s to better photography …
Al Hannigan
