How Does Aperture Effect an Image’s Exposure?

Your digital camera’s aperture setting is one of the three main settings that determines whether your image is well-exposed or not.

Inside your camera is a digital sensor that captures light. The sensor is covered by a pair of doors (the shutter, read more about shutter speed here), which open and shut to allow light in.

However, there’s also a circular door of sorts (called a diaphragm) that covers the sensor. This circular opening (the aperture) expands and contracts to effect how much light comes in and contacts the sensor (see the image to the left, courtesy of Wikipedia). In the top picture, the diaphragm is wide open, creating a large aperture and letting in a lot of light. Conversely, in the second picture the diaphragm is almost closed, creating a tiny opening and letting in a small amount of light.

How Does This Convert to Camera Settings?

The aperture setting on your camera is the one labeled with an ‘f’ – i.e. f/1.8, f/4.0, f/22. This number is a measurement of how big the aperture is.

It is also a bit non-intuitive. The larger the number, the smaller the aperture. So, for example, f/22 is an extremely small aperture which lets in a tiny amount of light. f/1.8, on the other hand, is a very large aperture and lets in a whole lot of light.

So, in terms of exposure, you want to open the aperture (turn the number down) to brighten your picture and close the aperture (turn the number up) to darken the picture.

As usual, though, there’s a trade-off. Read the next post to see how else the aperture effects your image.