Aperture in Photography



There’s plenty to learn when you’re starting out in photography, even if you’ve been taking pictures for a while, understanding how aperture affects your pictures can give you greater creative control and greatly expand your shooting options.

Which aperture to use

People often get quite confused when deciding what aperture to use with their camera, many never really move on from the safety of using the magical, green, ‘fully auto’ mode. All those f-numbers and semi-auto modes can surely take the fun out of photography for the uninitiated. There is however – pardon the pun – light at the end of the tunnel… and that’s really a clue, it’s all about light.

Remember, there are generally three things we can adjust to get the best exposure in any given scene. Shutter speed, ISO and aperture. You also have to factor in what lighting conditions you are shooting in as this will greatly affect what settings you use. For example, shooting exteriors at night will require very different camera settings to those used during the middle of the day.

Aperture basics

A cameras aperture, simply put, is an opening through which light passes. With our own eyes it’s the pupil which has the job of controlling the amount of light that enters our eyes by enlarging the radius of the opening to let more light in when it’s dark or by reducing the radius when it’s bright. A camera’s aperture works in a similar fashion.


F numbers

In photography, a cameras aperture is measured in f-numbers,
which is a way of describing the size or area of the aperture opening.
The smaller the f- number the wider the opening.

Different lenses have different capabilities and the better or ‘faster’
lenses are capable wider apertures and relatively low f-numbers.

Compare the two aperture sizes in the picture opposite. You can see
that at F/2.8 the aperture is set wide open allowing lots of light to
enter the camera as compared to F/22 where the opening is very
small allowing very little light to pass through.


It can be a little confusing try to understand aperture numbers and how they relate to the overall exposure. Remember too that camera lenses will vary in capability and range.

For example, a Canon 50mm EF prime lens has a range of between F/1.4 to F/22. However a typical zoom lens, a Canon EF 24-105mm has an aperture range of between F/4 and F/22.

We refer to the difference in aperture settings or values as ‘Stops’. For example, if we start at F1.4 and go through all the typical full stop values, they are as follows: F/1.4, F/2, F/2.8, F/4, F5.6, F/8, F/11, F/16 and F/22. These are called ‘Whole Stop’ differences, so when we start at the lower end of the scale and increase the aperture by one whole stop it allows twice as much light to enter the lens.

To add to the confusion most cameras are capable of increasing and decreasing aperture values in third and half stop increments for greater control over exposure.


One of the advantages of mastering aperture is the ability to understand its effect on the depth-of-field of any shot. Depth-of-field is essentially the area of a picture that is considered to be in acceptable focus and the aperture setting you use can greatly affect this.



If you take a look at the examples opposite you’ll see
that using a wide aperture of F/2.8 reduces the area of
acceptable focus or the depth-of-field.

You’ll notice that the toy car in the foreground looks
sharp and in focus but the rubrics cube in the background
looks soft and out of focus.

When we change the aperture by selecting F/22 it then
results in an increased depth-of-field so that both of
the objects in are in focus.

The optical focus for both shots is the same and is
centred on the windscreen of the toy car. It’s the use of
different apertures that changes the depth-of -field.
This is particularly useful for the purpose of isolating
subject matter and is often used for portraits to blur out


Small or large aperture

If you’re deciding what aperture you need in any given scene, perhaps you need to think about what you’re trying to achieve and what your subject matter is. For landscapes and shots where you want everything to be sharp and in focus, including the foreground and background, then you’ll be better off using small apertures, so F/16 and above would be the ideal choice. If you want to isolate subjects such as people, flowers, insects and animals then perhaps think about using a wide aperture, so F/4 or lower would produce a shallower depth-of-field.

The best advice in this regard is to explore your camera and see what range it’s capable of producing.

Aperture priority mode

If you’re keen to explore the effects of aperture and how you can incorporate this into your own photography then perhaps think about using a semi-automatic mode on your camera such as ‘aperture priority’, where you set the aperture and the camera does the rest. You’ll find this is an easier way to experiment with various apertures. Take some notes and see how the other settings such as shutter speed and ISO are affected.


Remember, that aperture has a direct relationship with depth-of-field so the lower the f- number the shallower the depth-of-field will be. Another thing to remember is that this might not be so noticeable if you are using a wide-angle lens, but zoom in a little and use a longer focal length and you’ll soon see the difference.

© Mark Sutton 2015

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