In the last few weeks we have been talking about exposure and the settings that control it.
In the last post, we saw the creative control that working with one of these exposure settings–shutter speed–can give you in terms of how movement appears in a photo.
In this post, we’ll look at the aperture setting, another of the exposure controls, and see how you can use it to enhance your photos, direct focus onto your subject and give your images a sense of dimension.
The aperture is the opening in your camera's lens.
The size of this opening determines the amount of light that gets into your camera and reaches its image sensor. A larger opening lets more light in and a smaller opening lets less light in.
The aperture size is measured in f-stops. The larger the f-stop, the smaller the opening in the camera’s lens. So an aperture of f/2.8 is larger than one that’s f/16.
This inverse relationship between aperture size and f-stop number can be confusing at first.
If you are mathematically inclined, you’ll understand this better if you know that f-stop numbers are actually the denominator–the bottom part–of a fraction. With that in mind, it makes sense that the aperture size gets larger as the f-stop gets smaller. The value of a fraction increases as the denominator increases. (And, BTW, if you’d like to dive into the details of all this, check out Understanding Apertures and F-Numbers.
Otherwise, the way that the f-stop numbers relate to aperture size is something that you’ll simply have to memorize. But the good news is that, once you begin working with the aperture settings, it doesn’t take too long for this idea to become routine.
The choice of aperture size changes the look of an image in two ways.
The amount of light that hits the image sensor increases as the aperture size gets bigger. Aperture size is an exposure control and as it changes, so does the brightness or darkness of an image.
The size of the aperture opening affects the depth of field in an image.
"Depth of field" refers to how much of your scene is in focus. As the size of the aperture gets larger (and the f-stop number gets smaller), the depth of field gets shorter. For example, the depth of field at an aperture of f/16 is deeper than at f/2.8.
So a small aperture produces an image with a deep depth of field, where most or all of the scene is in focus You can see this in the landscape photo below:
As the size of the aperture increases, the area of focus becomes smaller. A large aperture creates a photo where your subject is in focus, but the area in front and behind that subject is soft and blurry.
We’ve seen that you can control how much of an image is in focus by changing the size of the aperture opening.
But you might wonder, “shouldn’t I want all of my image to be in focus?" No, not always. It really depends on the scene that you are photographing and the story that you want to tell about that scene.
By controlling the depth of field, you can control how your viewer sees your photo. Selective focusing allows you to guide your viewer through the photo, helping them to know what part of it is important–the subject.
There are times when you will want to have the whole image in focus. In those cases, using a small aperture (large f-number) will keep the entire scene, from foreground through the background, relatively sharp.
So, for example, landscape shots usually work best when everything in the scene is in focus.
The same goes for cityscapes and many architectural images.
A deep depth of field is the way to go anytime the objects in the foreground and/or background are an important part of the image that you are capturing.
On the other hand, a shallow depth of field lets you create a blurry background behind your subject. So by using a large aperture opening (small f-number), you can employ a creative technique that puts the focus on your subject by effectively eliminating the background in terms of your viewer’s attention.
For this reason, a shallow depth of field is often used in portrait photography because the soft background ensures that subject is the main focal point of the photo.
Images of flowers and other small subjects often benefit from a shallow depth of field because the soft background frames and showcases the subject so that it stands out within the scene.
A shallow depth of field can be useful whenever you want your subject to stand apart from its background or when the background is unimportant in the image. A shallow depth of field can also give the illusion of depth and dimension.
The use of a shallow depth of field can instantly improve an image by simplifying a crowded background and removing the distractions of a busy, cluttered scene.
You can see this in action in the two photos below.
This first image was shot using a aperture setting of f/29. It’s a mess! The photo is crowded and cluttered and the focal point gets lost in the distractions.
But we see a big improvement in the photo when we open the aperture up to f/2.8. The now soft and blurry background compliments rather than competes with the subject.
And, finally, taken to its extreme, a very shallow depth of field can create an image that’s soft, ethereal, charming, magical…
Given these many examples, you can see the enormous creative power that the aperture setting can give you.
If you are still unsure of how the aperture affects the look of your photos, the short video below may help. We put it together quickly, but it will hopefully help you visualize how the appearance of an image changes as the aperture size gets larger.
Here are some things to keep in mind when working with apertures.
Keep in mind that three factors affect the depth of field: the aperture size, the focusing distance (the distance between you and your subject) and the focal length of the lens. The aperture is the easiest of these factors to control because it can be changed without moving the camera or recomposing the image, but all three can be used to change the look of an image.
We saw above that an very shallow depth of field can create soft, abstract-type images that leave parts of your subject blurry and out of focus. And that can be good. But not always.
Extremely narrow depths of field are part of life in macro photography, but you can run up against them whenever you are shooting wide-open. If that creates a result that you don’t like–if, for instance, you are shooting a portrait and you find the the depth of field is so shallow that your subject’s eyes are in focus, but the nose isn’t–here are some things that you can try:
Keep in mind that the area of focus is determined by your focusing point. There’s a range of focus in front of and behind that point. That means that, when shooting a landscape scene, if you set your focus point at the horizon, a portion of your area of focus will actually be beyond the horizon.
Instead, in order to maximize the sharpness of your photo, try to focus on a point that is about a third of the way into the frame.
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For the last several posts, we have been talking about exposure and how we can use it to creatively change the look of our photos. And in our previous post, we looked at using the aperture settings to change the depth of field of an image.
In our last post, we talked about shutter speed and how it affects the way motion is portrayed in an image.