Physically, the aperture is produced by a group of leaves that can be adjusted to allow either more or less light to enter your camera. These leaves can slide together reducing the aperture. The aperture determines how much light is allowed to enter the lens.
        The f-number printed on the lens indicates the maximum amount of light that the lens system is capable of letting in.  F-numbers are calculated by dividing the focal length of the lens by the diameter of the aperture opening. Consequently a 35 mm lens with an aperture opening diameter of 12.5mm results in an aperture value of f/2.8 (35 / 12.5 = 2.8)

        When trying to shoot a badly lit subject it is a good idea to increase your lens aperture, that is, adjust your aperture to a low f-number in order to allow more light to enter the lens. If your subject is, on the other hand, very brightly lit, it is a good idea to use a smaller lens aperture.

        You generally get the best results with a circular aperture.  The more leaves the aperture mechanism has the more perfect the circle of the aperture will be. For this reason the number of leaves of the lens is an important indicator of quality.

         You have just been given the technical explanation of what aperture is. It may seem a little complicated, but there is, however, no reason to be alarmed. Understanding the practical ways of using aperture is much more important.

F-numbers (F-stops)

The lens aperture value is indicated in f-numbers also known as f-stops. The amount of light allowed to enter the lens is either doubled or reduced by half whenever you adjust one stop up or down the scale, e.g. twice as much light enters the lens at f/4 than at f/5.6.

 Standard f-stops:

 f/1.8, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32

 
Aperture Regulates Light
Aperture is extremely important to the outcome of a photo because it is this tool that allows you to control effectively how much light passes through the lens. The combination of controlling aperture and shutter speed allows you to shoot in almost all kinds of light imaginable.
        A low f-stop combined with slow shutter speeds will allow large amounts of light to enter the camera and this will allow you to take photos in, for instance, the dusk when only little natural light is available.
        A high f-stop value combined with a relatively fast shutter speed will only allow little light to enter the lens, this will enable you to shoot in even very intense sunlight.
 
Aperture and Depth of Field
Aperture decides the depth of field (DOF), that is, how large a part of an image is sharp. Consequently, depth of field is an important creative tool you can use in your photography.
     In some cases it may improve your photo if the background is blurred and the focus is solely on the main subject (shallow depth of field). For other photos it may be better that foreground, middle ground, and background are sharp (large depth of field).
     A low f-number, e.g. f/2, results in a shallow depth of filed. A high f-number, e.g. f/32, results in a large depth of filed. In between these extreme settings the lens provides you with many settings to choose from, making aperture an important creative tool. The focal length of your lens will also affect the depth of field. This is, however, described later on in the school of photography.  

 
How to Use Aperture
All photographers and camera manufacturers agree that aperture is an important tool in photography. Regardless of the make of your camera the aperture control is easily accessible and simple to adjust.
        The aperture is generally controlled using a control wheel that allows you to move quickly up and down the f-stop scale. Being able to adjust aperture instantly is a great advantage, particularly, if you are shooting in a situation where unexpected subjects can suddenly present themselves or in a situation where the available light may change without warning.

        You will most likely find the mode dial located on top of your camera housing. Depending on what model your camera is, the name of this wheel may vary slightly. Using this dial you can choose between the semi automatic modes S (on some cameras this is called T or TV) and A (or AV). These letters are different abbreviations of shutter priority mode (S) and aperture priority mode (A).  

Using a wide-angle lens allows you to get a very high depth of field. Using a high f-number (e.g. f/8-f/32) you can get some really good results.

 
If you are interested in working creatively with aperture you should choose mode A. In this mode you adjust aperture as needed, and the camera subsequently finds a corresponding shutter speed. Alternatively, you can choose the M (manual) mode that allows you to control aperture as well as shutter speed.
        Most cameras have a P (program) mode, in this mode all parameters are controlled automatically. If you really want to be in control of your camera, and consequently your photos, we recommend that you avoid using this mode.
        Aperture is one of the features that you need to be able to adjust instantly, precisely, and without having to think too much. For this reason it is important to know the controls and modes of your camera before you do any serious photography. If you consult the manual of your camera you will find much more information about the possibilities of your equipment.
        If you have never before used aperture as a creative tool in your photography we recommend you to start right away. You will see results in no time.
 
You have now learnt something about aperture, and if you have not already read about shutter speed, reading more about this topic would be the next step. Otherwise we move you on to more knowledge about focus or ISO values, both of which are important tools. 
 
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