All you could ever want to know about aperture (and more)

If you’re feeling a little rusty on camera functions and settings, or simply want to brush up on your basic knowledge then you could do a lot worse than watching this video presented by photographer Andrew Boey. It is quite literally everything you could ever possibly want to know about aperture!

Now as always, this tutorial is giving us the main rules, but rules are there to be broken, so if you disagree with any of them not to worry. There are always going to be plenty of exceptions to any rule, but this is a great place to start. So let’s dig in!

1. What f-number should you use? Andrew explains that there are 3 basic genres that help you determine which f stop to use: people, places and things. For portraiture, you generally want to separate the subject from the background. Of course, you can do this with lighting, but you can also do this by choosing an appropriate aperture that will blur out the background and leave the subject in focus. Andrew suggests anything between f/2 and f/4, but obviously, it does depend on the lens you are using and how close to the subject you are. Shooting places (ie. scenery and landscapes) depends on the time of day – in daylight you will have enough light to shoot at f/11 or f/16 to render the entire scene in focus, at night or dusk he suggests using f/5.6 or f/8. For macro, he says to use anywhere between f/8 and f/22 because you are so close to the subject.
2. When do I change the f-number? Here he answers two questions. The first is what order should I choose the aperture when setting up the exposure for a shot? Andrew recommends starting with the ISO. When he first walks into a location he looks at the amount of available light and adjusts as appropriate. Then he chooses the aperture value. Of course, if he’s shooting sports for example then he will adjust the shutter speed before the aperture. The second question he answers is when do I need to change the aperture? The answer: when the background changes. You need to decide how much background detail you want to be showing.
3. What is an f-number? Andrew tells us that it is the focal length of the lens, divided by the diameter of the lens aperture. Simple! He then demonstrates how this works by physically measuring the hole. Generally, more expensive lenses have a wider difference between the minimum and maximum apertures, and also tend to be faster.
4. Effects of f-numbers. They allow you to blur out a background (and foreground), ie. you can alter the depth of field (that’s the amount of front to back focus you get in an image). The next effect is that it lets more or less light into the camera. This is also important if you’re shooting with flash because changing the aperture will affect how much light falls on your subject and doesn’t affect the light on the background.
5. Why does my f-number change when I zoom? Going back to number 3, with a zoom lens essentially you are changing the focal length of the lens. However, there are lenses (usually more expensive ones) that keep the f-number constant. These are called constant aperture lenses. The way that these work is that they keep the length of the lens consistent.
6. What are the f numbers? f numbers are stops of light:f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 etc are the true stops. The other f numbers you may see are not true stops in that they are 3rd stops of light.
7. How do you learn f stops? Andrew says to ignore the non-true stops and to just concentrate on the true stops. The true stops are roughly doubled in a series.
8. What are f stops? A stop is basically the movement between one f-number and the next in the series. So moving from f/2 to f/2.8 is moving up one stop.
9. How is the f value different from the T value? F numbers are a little vague in terms of what the actual image will look like because the outcome varies wildly depending on what lens and camera you are using. The T value is the light transmission efficiency and is the actual measurement of how much light is going through the lens.
10. Is f-number depth of field? No, although they are related. By increasing the f-number you get an increased depth of field, but it depends on how close the camera is to the subject.

Finally, Andrew recommends if you’re unsure, to start with f/8 as it is in the middle of the range, and you can then adjust things from there.