This is part one of my Essentials of Photography series. The control that never stops being important, is key to understand in all shooting environments is your aperture. So let's jump right in.

The aperture is a series of blades inside your lens that open and close to control the amount of light allowed through. It also controls depth of field, that is, how sharp things are in front of and behind your subject. (More on depth of field soon)

The size of an aperture is referred to as f/stops. See the handy guide below:

So a larger opening, allowing through more light, will correspond with a smaller number, such as f/4. A small amount of light, coming through a smaller opening, will be designated with a larger number such as f/22 or f/16.

Now go ahead and turn your mode dial to A or Av to enter your camera’s aperture priority mode. In this mode you select the aperture and your camera decides other factors to give you a properly exposed photograph.

When you find yourself in low light situations you need to get the most amount of light through the lens that’s possible, so you should shoot at the maximum aperture; that is the lowest f/number on your particular lens. Conversely, in bright light you may need to select a higher f/number.

Let’s take a look at some situations in which you might use one aperture versus another.

I took this first image in my living room, but it was relatively dark. So I opened my lens to F/1.8, the brightest it could go. Notice how shallow the depth of field is here.

Here I was shooting a landscape in bright daylight. So I had lots of light to work with. Also, I wanted a long depth of field. So this image was shot at f/11.

Depending on your camera it will have at least one rotating control dial, either on the back right shoulder of your camera or in front near the shutter release. Spin this dial when in aperture aperture priority mode and you’ll see your f/number change.

We’ve barely scratched the surface on the topic of apertures here – just get comfortable with controlling yours from aperture priority, experiment and enjoy. We’ll discuss more about how aperture controls the depth of field and its relationship with shutter speed and ISO in subsequent modules.