Ben Crawford Photography | Freelance Travel, Landscape and Lifestyle Photographer

Photography Tutorial #3 Aperture

Posted on 24 May 2010 | by Ben | Filed under Blog

The last tutorial I wrote was a basic summary of exposure, so now let’s look at exposure in more detail by exploring aperture, one of the key variables we can use to manipulate it.

In simple terms the aperture is the hole in your lens. This hole can be made bigger or smaller and therefore it controls how much light is let in through your lens and onto your camera’s sensor. The bigger the opening – the more light, the smaller the hole – the less light. If you look down into your camera’s lens you will see what I am talking about. It looks and works pretty much like a human eye, with the iris opening and closing to control the flow of light.

The aperture setting on your camera is expressed as an f-stop value which typically ranges from around f2.8 through to f22, but this will change depending on your camera and lens. A small f-stop number means the aperture, or opening in your lens, is big, while a large f-stop number means the opening in your lens is small.

We already know from my previous post that exposure is a combination of aperture and shutter speed. This relationship is in fact a direct one. The more light you let through your lens via controlling the aperture, the less time your shutter needs to be open to allow the correct amount of light to pass onto the sensor and create the optimum exposure. I’ll cover shutter speed in my next tutorial but it’s important to remember this direct relationship.

If you have your camera set on Automatic then it is constantly calculating what it believes to be the correct exposure and then adjusts your aperture accordingly, along with the shutter speed, to create a photograph. A lot of the time this automation produces good results and you don’t have to worry about anything. Just point and shoot. However by having just a small understanding of what your aperture (and shutter speed) settings are doing to influence your image, will mean you can switch off your automatic setting and take dramatically better photos.

Have you ever noticed a photo where the subject is perfectly clear yet the background is blurred or out of focus? Or alternately, have you looked at a landscape photo and seen a perfectly focused image from foreground to background? This is what is known as the ‘depth of field’ of an image and you control it through your aperture setting. To achieve a shallow depth of field (i.e. only a small portion of the photo is in focus) then you need to set your aperture to a small f-stop value like f4. If you want to have your whole image in focus, set your aperture to something like f18.

This image above of Westhaven Marina in Auckland was shot at an aperture setting of f22. Note how how the image is clear from the boats in the foreground through to the skyline in the background. There is some slight blurring of the boats but this is due to the long shutter speed of 20 seconds. During this time the boats have moved slightly with the waves and created a nice motion effect.

Compare this to the image below of a boat in Marseille. This has been shot at f2.8. You can see the difference. A very selected area of focus with the rest of the image blurred. By taking a detail or portrait shot like this you are able draw attention to the subject of the photo. In comparison the shutter speed of this image was 1/800th of a second which shows the direct relationship between aperture and shutter speed – the bigger your aperture (a small f-stop) the faster your shutter speed needs to be and vice versa.

Right, so now you know the theory, let’s have a play. I’m going to assume you have a dSLR, but the majority of compact cameras will also allow you to alter the aperture setting. It is more than likely that you will have a ’setting selector’ in the form of a dial. On a non pro Nikon it has M, A, S, P, AUTO then a number of pictures depicting shooting situations. A Canon is very similar.

In AUTO your camera is doing everything and you have no way of controlling any setting. M, or Manual, gives you 100% control of all settings. However, very conveniently, your camera has been built with a half way setting called Aperture Priority (the A setting on the selector). Basically this gives you the control over the aperture setting while your camera will adjust the shutter speed automatically to ensure you still take a good photo.

Have a play – switch your camera to A (or its equivalent on your camera – most likely AP or Aperture Priority) and then set the aperture to something like f5 and take a photo. Then try it at f18. The more you experiment the better your understanding and use of aperture control.

Being in charge of your aperture is vital to improving your photography. It will give you far more creative control so you get the effect you want and it will ensure your portraits pop and your landscapes are crystal clear.

To round off the basics of exposure control, I’ll cover shutter speed in my next tutorial. But in the meantime, happy shooting!