Aperture refers to an adjustable opening in a camera lens that regulates the amount of light reaching the camera sensor.

This makes more sense when you understand that a camera lens contains blades (as illusttrated by the image below) which slide together to form a hole once the camera button has been pressed to take a photograph.

When you use the automatic mode of your camera it will (as you would expect) automatically decide the best aperture setting to use, however by switching your camera setting to aperture mode AV or A (depending which make of camera you have) you can manually decide the size of the aperture, the camera will then select the right shutter speed and ISO, these three elements are sometimes referred to as the exposure triangle which we will go through in a later article.

Making Sense of aperture settings

To start off, it is worth pointing out that it is actually the lens you use and not your camera that dictates the aperture options available for you to use.  The variations in the aperture size (the size of the hole) are defined by using numbers.  The smaller the number the bigger the hole.  It is usual to see a lower cased f before the number, this is an abbreviation for focal ratio, sometimes referred to as an “f-stop”.  When taking photographs where light is limited your camera will automatically choose a larger f-stop (such as f/4) to allow more light into the camera.  Conversely when there is too much external light a smaller f-stop (such as f/16) will help to avoid the images becoming over-exposed.  To avoid confusion the words smaller and larger refer to the size of the hole and not the number used.  Hopefully the following diagram will help things to click into place for you (pardon the photography pun)!

Why use different apertures?

You may be wondering why you should experiment with different aperture settings.  Well let me just give you a few reasons why it is important or beneficial to have the ability to adjust the aperture setting you use.



Apart from regulating the flow of light going into a camera, aperture settings also control something known as “Depth of Field”.  Depth of field can be described as the distance between the nearest and farthest objects in an image that appear acceptably sharp.

An aperture of f/2.8 was used creating a shallow depth of field.

An aperture of f/18 was used creating a deep depth of field.

The two images above show the difference between a shallow depth of field, where the background is blurred and a deep depth of field where the detail in the background is still in focus despite being quite a distance from the foreground object (in this case the bride & groom).

Using a wide aperture (small f/ number) when shooting portraits will blur the background which can create a really nice effect, especially if you want to avoid any unwanted distractions.  In contrast to this, if you want to ensure the background is sharp (as in the second photograph) you will need to make sure you use a smaller aperture (higher f/ number).

Using a wide aperture (small f/number) is great if you only have one or two people as the subject(s) of the photograph.  If you are photographing more than 2 or 3 people you will need to ensure you use a smaller aperture (higher f/ number) to make sure everyone is in focus.



There will be times you will want to increase the exposure time (the duration the shutter stays open) to create certain effects.  The above image is a photograph I took in Oxford Street, London.  I extended the shutter speed to 1.3 seconds because I wanted to capture the busy hustle and bustle of the people moving, and wanted their movements to become blur (motion blur).  As the shutter was open for longer than it would normally be, I had to reduce the aperture to f/22.  If I had kept a wide aperture say f/4 for instance, too much light would have entered the camera and it would have overexposed the image.

Which setting should you use?

To be honest, in a lot of situations it is probably better to leave the camera to decide the aperture setting.  Cameras are very good now and leaving your camera in automatic mode can take a lot of stress out of taking photographs whilst delivering great results.  Without trying to sound contradictory however, I would encourage you to play around with the aperture settings so you can see for yourself how changing the aperture can effect your images.  Once you are familiar with and comfortable using various aperture settings you can revert back to automatic mode for the most part and then switch to aperture mode when you want to create a specific result/effect.

Final Thoughts

At first the concept of aperture can seem quite daunting, which is why I have tried to keep this explanation as simple as possible.  In most instances the best way of learning new concepts and ideas is through practice, trial and error.  Remember “The man that never made a mistake never made anything”.