Aperture is the adjustable iris in your lens, made from thin metal blades that move together to form a circular opening, which varies in size. This opening controls how much light enters the camera.
Aperture is measured in f/stops, for example f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and so on. Moving from one f/stop to the next doubles or halves the size of the opening, as well as the amount of light entering your lens.
Photographers refer to the adjustment of this opening as “opening up” and “stopping down”, this simply means, making the size of the hole bigger or smaller.
The most important thing to remember about aperture is that a large aperture (represented by a small f/number) produces shallow depth of field, while a small aperture (represented by a big f/number) creates a large depth of field with much more of the image in sharp focus.
Let me explain this a little more in detail…
A large aperture (small f/number) allows more light to reach the sensor, allowing you to chose a faster shutter speed. Using a large aperture is especially useful when shooting in low light conditions, or when photographing fast moment. Opening your aperture means you have a better chance of freezing action.
A small aperture (big f/number) allows less light to reach the sensor, meaning you can choose a slower shutter speed. A small aperture also increases the Depth of Field, resulting in much crisper, sharper images, especially with long distance shots such as landscapes.
Depth of Field
By adjusting the aperture, we control the amount of Depth of Field (DoF) in the photo.
Depth of Field is the amount of the photo that is in focus. A large Depth of Field means that most of your image is in focus, while shallow Depth of Field means that only part of your image is in focus, and the rest is blurry or fuzzy.
Shallow Depth of Field
To create a blurry background, chose the smallest f/number possible, zoom in, get close to your subject, and create as much distance between yourself and the background as possible.
Large Depth of Field
On the other extreme, to create a large Depth of Field that is as sharp as possible, chose the biggest f/number practical, stand back from your subject, and zoom out.
Stay tuned for the next lesson on ISO and the Exposure Triangle…