In a previous article, we looked at depth of field and how it helps to determine what is in focus in a photo. We can use it to maximise sharpness in landscape images. We can also use it to isolate subjects in portraits by minimising distracting backgrounds. Let’s look at how it relates to aperture.
Why Use Aperture priority?
You use aperture to control the depth of field. Aperture is how wide your lens can open and is probably the most difficult mode for beginners to grasp when they’re learning about all the different modes on their camera. But once you understand it, it opens up a whole world of creativity.
Switch to aperture priority using the main dial on top of your camera. It’s marked A on a Nikon or Sony and Av on a Canon.
While in Aperture priority, you have control to set the aperture and ISO. The camera automatically picks the correct shutter speed for you. Aperture is measured in numbers known as F-Stops. The bigger the aperture, the more light that comes through the lens. The smaller the aperture, the less light that will enter the lens.
But why use one aperture over the other? Besides controlling the amount of light that gets into the camera, aperture also controls the depth of field.
Depth of Field – Again!
Apertures like F1.8 or F3.5 are large and allow lots of light to hit the sensor. They also give a nice shallow depth of field and are perfect for portraits. This shallow depth of field helps to separate the main subject from the background. You’ve often seen photographs, where a persons face, is in focus and the background is blurred. This is the result of using a large aperture. Using a large aperture is generally considered the best method for shooting a portrait.
A small aperture like F14 or F22 means more of the photograph will be in focus, which is something that’s desirable for landscapes. Small apertures allow less light into the camera. However, in aperture priority, the camera will pick a shutter speed to compensate for this.
All lenses are marked with their aperture range. If you see a lens that is a 50mm F1.8, this means the largest aperture is F1.8.
Many kit lenses will have a largest range of F3.5-5.6. This means that when the lens is zoomed
out to the widest position the maximum aperture is F3.5. When the lens is zoomed in all the way it will have an aperture of F5.6.
The important thing to remember is that a large aperture like F1.8 lets in more light and gives a shallow depth of field. A small aperture like F22 lets in less light but gives a deep depth of field.What aperture you use depends on what you are shooting and the type of lens you are using.
For group photos like this, use a mid-range aperture like F8. This ensures a depth of field that will keep the people in the back row and the people in the front row in perfect focus. Keep the important people to the front and centre and ensure all faces can be seen.
What Else can Aperture Control
Aperture can also help in other situations. If I am shooting in a location where the light is poor, I can increase the size of the aperture, allowing more light in.
This photo was taken inside a dark marquee at the 2013 Westport Music Festival.
Using a small aperture of F1.8 allowed me to get enough light into the camera to get a perfectly acceptable shot.
Make sure to get your single focus point on the subjects face.
In short; Lower numbers such as F4 and below will give a shallow depth of field. Higher numbers such as F14 and above will give a deep depth of field.
When I first started out, it took me a while to get my head around the entire concept of aperture. I found the following exercise very beneficial.
Get a small statue. Set your camera to aperture priority. Using a single focus point, focus on the top of the object – in this case, the head. Allign the metering gauge in both shots to ensure correct exposure. Take a shot at the largest aperture (Low number) of your lens. Now take a shot at the smallest aperture (Big number) of your lens.
Compare the shots and look at the backgrounds in each. What effect does it have?
Now, try zooming all the way in at the largest aperture and at the smallest aperture. What effect does this have? See what effect it has when you move the statue closer to the camera and then move it closer to the background.
Move on to shooting the same exercise with a friend.
Back To The Hub