Aperture and F-number

A camera's aperture is a hole or an opening through which light travels. Each camera has a diaphragm that can grow and shrink. When the diagram grows, it yields a big aperture. In contrast, when it shrinks, the aperture is narrowing.

By controlling the diagram so as the aperture, the camera is able to rule the amount of light that passes through lens to film or image sensor. The shutter speed is certainly affected by the size of the aperture as well, i.e., the bigger aperture a camera uses, the faster the shutter speed is.

F-number is the unit or measurement of the aperture. We can find the F-number from the following formula.
F-number = f / D where f is a focal length, and D is an effective diameter of the lens opening

It's not necessary to remember this formula. Knowing how to interpret the F-number is more than enough. So, just remember the F-number has negative relationship with the size of the aperture. In other words, the less F-number means the bigger aperture. Likewise, the more F-number means the smaller aperture.

The above picture shows that F2 yield bigger aperture than F11. As a result, by using F2, we get faster shutter speed (less time to receive enough amount of light).

When you shop for the right PowerShot, don't forget to compare the F-number of each model. For example, the PowerShot SD1200 IS has an aperture range from F/2.8 to F/4.9 while the PowerShot SD780 IS has a range from F/3.2 to F/5.8. So, what does it mean? It means that the SD1200 has an ability to open wider aperture, so it can take pictures with faster shutter speed. We also say that the SD1200 has a faster lens than the SD780. Usually, the less F-number a camera has, the better a camera is.


(pictures source: go_med @ rpst-digital.org)


See also
ISO, Aperture, and Light Condition part 1/2
ISO, Aperture, and Light Condition part 2/2
Aperture and Depth of Field
Learn about Shutter Speed and why it's so important

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