Photography Basics : Aperture

What is aperture and why is it so important? Do you use manual settings on your DLSR or priority based settings?

In photography, light is the most important external property that affects an image. On the camera, there are three main settings that help you adjust the light on the sensor – or exposure.

So aperture affects the amount of light hitting the sensor. With light, too much and the image is bright and overexposed. Too little and the image is dark and underexposed.

Let me explain how aperture behaves on the camera and it should become clearer on how it works. Behind the lens and in front of the sensor are a ring of petals that form a hole for the light to pass through. Aperture can increase or decrease the size of this hole. It stands to reason that the larger the hole, the more light is let in. The opposite occurs when the hole is smaller.

However, the camera settings are somewhat confusing for the aperture setting – the following is a range with the size:

So as the number gets higher the width of the hole gets smaller – letting in less light. You can see this effect by holding your fist in front of your face and making a tiny hole to look through. The larger this gap is the more light is observed.

But the main reason for the aperture is focus so how can the above assist with that? Depth of field and focus are two important terms in photography that come together when setting the aperture.

Depending on the result you would like in your image, you need the focus to be right. For instance, a landscape photographer usually requires everything to be in focus.

That includes objects close to the camera, in the mid-range and things that are far away. Someone taking a portrait only needs the area from the tip of the nose to the back of the head to be in focus, sometimes less. This is known as depth of field or DOF. The image below is focussed on the pier but because the setting is f5.6 the runner and pathway are out of focus.

So how does aperture change the depth of field? The smaller hole gets more in focus – in my opinion up to about f16 – after this, there is not much difference, in fact, it can degrade. With a medium setting (f8) you’ll get a good range but things far away will not be in focus. At f4 the range of focus is finely tuned – if you train your camera on the wrong point, the image won’t work as you expected. Some nature and macro photographers will use wide settings like f2 to pinpoint on a particular part of the subject.

Obviously, when taking a photo at f4 you are going to let in a lot of light. Depending on the conditions you will need to adjust the shutter speed and ISO accordingly. A lot of photographers, myself included, will use aperture priority setting. This means the camera will balance the shutter speed for you automatically.