Aperture Explained

Now, we have come to the next important element of exposure, namely “aperture”. Aperture is the fancy word for lens opening and is measured in F Stops.

It works as follows: the smaller the F number; the larger the lens opening (i.e. F/2.8). On the other hand, the higher the F number; the smaller the lens opening (i.e. F/22). So if your lens has a maximum aperture of F/2.8; that will be the setting you will use to allow the most light to flow into the camera through the lens. If your lens has a minimum aperture of F/22; that will be the setting you will use to allow the minimum light to enter the camera. 

  

It may not make sense now, but if you look at the following visual illustrations you will get a better idea of how aperture works:

• The lens I have used for this excersise is a 50mm f/1.4, which means that the largest aperture available on this particular lens is f/1.4. The image above shows a massive lens opening at f/1.4 that allows ample light through. Since the lens allows so much light rhrough it means that you can shoot with decent shutter speeds even in bad or deterioating light.

• At f/16, this lens is "stopped down" to its smallest aperture. At f/16 it is therefore near impossible to take any sharp pictures out of the hand in deterioating light. The shutter speeds are so slow at f/16 that  you have to use a tripod to prevent blurry shots.
  

If you carefully study the above images you will find that with each change in F stop to the next F stop; the light entering the camera is halved. Example, F/2 will allow twice the amount of light to enter the camera than with F/2.8, which is the next F stop in the chain. F/2.8 on the other hand, will allow twice the amount of light to enter the camera than with F/4. F/4 will allow twice the amount of light to flow into the camera than with F/5.6 etc...

The diagram below shows the standard F-stops, ranging from F/2 up to F/90: 

F1

F1.4

F2

F2.8

F4

F5.6

F8

F11

F16

F22

F32

F45

F64

F90

Lens opening

Very large to large

Medium

Small to very small

Best suitable for

Low light shots and portraits where you want to render a single element in sharp focus and the fore and background out of focus.

For General shooting. Ideal for Group shots

Suitable for landscape shots where you would want all elements in the image in focus.

Take note that the whole range of F stops are not necessarily available on all cameras i.e. a lens may offer a maximum F stop of F/4 to a minimum F stop of F/22. Most cameras also have the capability to increase F stops in 1/3rds, i.e. F/4 – F/4.5 – F/5 to the next full stop, which is F5.6. 

Our next lesson will cover the relationship between aperture and depth of field. 

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