All digital SLRs and many point and shoots can operate in manual or semi-manual modes. If you capture most of your photos using Auto mode it’s time to look at some of the benefits you can get by switching to semi-manual operation.

With these modes you control the aperture or shutter speed and you get a chance to capture more creative photos. So how do you do this and what settings do you use? In this series, I’ll explain your camera’s Aperture Priority and Shutter Priority (Av and Tv) modes and also explain why your ISO setting  is important to understand too.

If your camera can operate in manual mode you’ll have settings such as M, Av, Tv and P on your camera’s dial. The two settings we’ll focus on are Av and Tv where you set the aperture or shutter speed yourself.

What is Aperture?

This begs the question, what is aperture and what is shutter speed? Aperture is, very simply, the size of the hole through which light enters your camera. The larger the hole, the more light gets in.

Aperture is described using an f number which is calculated using a complex formula. A rough rule of thumb is to think of aperture being a fraction so an f number (often called a f-stop) of f/2.8 is bigger than f/22 for example.

Understanding aperture

Aperture not only has a direct relationship to the amount of light let in to the camera, it also affects depth of field. When you use a large aperture such as f/2.8 you will get a small depth of field so only a small distance in front and behind the point of focus in the photograph will be in sharp focus and the remainder of the image will be out of focus.

Depth of field is a creative tool that many photographers use to their advantage. For example, when photographing a beautiful flower, you’ll want the focus to be on the flower and not the things behind it. Using a large aperture such as f/2.8 throws the background out of focus. The photograph at the top of this post is an example of a large aperture and a small depth of field.

On the other hand, using a small aperture such as f/8 or f/11 gives you a large depth of field so everything in the photograph will be in focus – useful when photographing landscapes for example.

The relationship between Aperture and Shutter speed

When you set the aperture using the Av setting on the camera, the camera sets the shutter speed to an appropriate value. This is because there is a direct correlation between aperture and shutter speed.

When you use a small aperture, only a small amount of light comes into the camera so you need to compensate for this by using a slow shutter speed to ensure you capture enough light.

On the flip side, when you use a large aperture such as f/2.8, you get lots of light so the camera will set a fast shutter speed.

When you use Av mode, you’re effectively saying, I’ll set the aperture I want and you – the camera – are to adjust the other settings to give me a good picture. When you are in Av mode, there will be a dial or other option you’ll use to set the desired aperture value.

Helen Bradley