Photo 101 – Aperture Explained

One of the key elements to taking good photos is to make sure you have the correct exposure; you don’t want it too dark or too light, you want it just right (like Goldilocks). There are three factors in setting the correct exposure, often referred to as the “golden triangle”.

1. Aperture
2. Shutter Speed
3. ISO

Camera lens and aperture by nayukim, on Flickr

In this article I will attempt to explain the first of these – Aperture. You may have heard aperture referred to in a number of ways. Have you ever heard someone talking about “f-stops” or “fast glass”? These are referring to the aperture of the lens. Aperture refers to the opening where light enters the lens. This is made up of a number of blades that overlap and can change the size of the opening to let in more (or less) light. Changing the size of the aperture has a number of effects:

• It will affect the exposure of your image, allowing you to control how bright or dark the image is.
• Depending on whether you’re using a large or small aperture, you will need to change the shutter speed to compensate (in order to achieve the same exposure)
• It will change how much of your image is in focus.

You can probably think of situations where you might want more light to enter the lens; dark indoor environments and night time photos are a good example. In order to do this, you will need to increase the size of the aperture. The size of the aperture is indicated by an “f-number” or “f-stop”. Without getting into the technical reasons behind it (if you’re intereseted, read this), you should know that larger apertures are small f-numbers like f/1.8 or f/2.8, and smaller apertures are the bigger f-numbers like f/16 or f/22. Below is a diagram illustrating the size of the aperture (the hole where the light comes through the lens) for different f-stops.

By increasing the size of the aperture, you increase the amount of light coming into the lens at any time. With more light coming in, the shutter doesn’t need to stay open as long to get in enough light. The result of having a faster shutter speed means you’ll get fewer blurry photos, but we’ll get into that in a later article!

One of the other side effects of increasing or decreasing the size of the aperture is that you will change how much of the image is in focus. Using a small aperture (remember, that’s a big f-number like f/22) means you’ll have a huge area that appears to be in focus in your image. Conversely, a large aperture (small f-number like f/2.8) means that only a select area of your image will be in focus. The term used to refer to how much of your image is in focus is referred to as “depth of field” or “DOF” – i.e. a shallow depth of field means that only a small part of the image is in focus. This is commonly seen in portrait photos where the subject’s face is in sharp focus, but the background is blurred out. This is great for drawing attention to the subject and covering up busy backgrounds. You could also use it in a family portrait – put your mother-in-law in the back row and focus on the front row

At the bottom of this page are four example photos taken in my garden to illustrate the effect that different apertures will have on your photos. You’ll notice that the backround is blurred out when using a large aperture (small numbers like f/1.8 or f/2.8) and is quite visible when using small apertures (like f/16). I should also mention that the focal length of your lens also affects the depth of field. Using a longer focal length (e.g. a 200mm lens instead of 55mm) will also create a shallower depth of field. The best thing for you to do is go and take some photos yourself to experience what you can do. Set your camera to aperture priority mode (usually “A” or “Av” on the dial) and take shots at different apertures, and try it at different focal lengths (e.g. 18mm, 55mm, 200mm) to see what effect it has.

REMEMBER: SMALL F-NUMBER = SMALL AMOUNT OF IMAGE IN FOCUS; LARGE F-NUMBER = LARGE AMOUNT OF IMAGE IN FOCUS

Happy shooting!

Shot “wide open” at f/1.8

Shot at f/2.8

Shot at f/8

Shot at f/16