Is your camera permanently stuck in Auto Mode? Would you like to get more out of your camera?

This is the second of four parts in a series looking at the different modes available on your camera, when to choose them and how to get the most out of them.

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Last time, we took a look at Program Mode as a way of stepping out of Auto Mode while still having a bit of a safety net.

In today’s post, we’re going to move a little bit further out of the comfort zone and take a look at Aperture Priority (shown as <Av> or <A> on your camera’s mode dial).

In Aperture Priority mode, you get to choose the aperture you want and the camera then picks the appropriate shutter speed to get the correct exposure for the scene.

But why on earth would you want to be able to do that? To understand, first we need to learn what an aperture is.

At its simplest level, you have two choices on taking a photograph: how wide to make the hole that lets light into the camera, and how long you’re going to let that light in. The technical term for the hole is aperture. The mechanism for letting the light in is called a shutter, and how long that shutter is open is referred to as the shutter speed. In combination, they determine how much light falls on the film or sensor and that is known as the exposure.

With me so far?

Now, it stands to reason that for any given exposure (total amount of light), the wider you make the aperture (hole) the shorter time you need to let the light through that hole (shutter speed). On the flip side, if you make the aperture really tiny, you’re going to need the shutter to be open a lot longer to get the same exposure.

Where it gets confusing, is that a wide aperture is represented by a small number and a narrow aperture is represented by a large number. This is because F4.0 (for example) is actually an expression of the fraction f/4.0 where f is the focal length of the lens. If you’ve glazed over the second I’ve mentioned fractions, don’t worry - you don’t need to know why to make use of it!

Now back to why you would want to have control over the aperture on your camera. The really exciting thing about controlling the aperture is that you can control the depth of field in your image. This is the distance in your picture that is perfectly sharp and in focus.

For example, you may want to take a portrait photograph having the subject in perfect focus while throwing the (rather cluttered and distracting) background into a pleasing blur. To do this you need to use a wide aperture (small F number). When taking a landscape photograph, however, you might like to have both the foreground AND the distant background in sharp focus - for that you need to use a narrow aperture (large F number)… but remember, the camera will set a slower shutter speed to get the right exposure, so don’t forget the tripod!

I can thoroughly recommend leaving your camera on Aperture Priority for a while and have a good play. You’ll learn how apertures and depth of field work far more intuitively by actually using them on a day to day basis.