Associate Professor of Art & Photography.
The aperture is one part of what I call, the exposure trilogy. In previous videos I talked about this…. along with the camera obscura. Remember how light can travel through a small hole in a wall, into a dark room and project an image of what’s outside on the opposite wall in the room?
The thing that makes this whole phenomenon possible is the hole through which the light is traveling. In photography we call that hole an aperture.
Every camera, from the camera obscura to the contemporary DSLR uses an aperture to control how much light falls upon your film or CCD chip.
Here is an important distinction to remember. Shutter speed controls how long light falls on your CCD, and Aperture controls how much light falls on your CCD.
Shutter speed – how long
Aperture – how much
Like the shutter and shutter speed, aperture also has two functions, one being a mechanical function in the camera and the other as an artistic tool.
The mechanics of the aperture are simple. It’s an adjustable hole inside your lens through which light passes. It’s very much like the iris in your eyes, which is also an aperture. If you’re in the dark, your iris opens to let more light in. When light intensity increases the iris closes. The function of the aperture is exactly the same in the camera.
The camera’s aperture is divided into increments called “f-stops”. You’ll find numbers on your DSLR that correspond to the size of the opening in the aperture. Here is an example of what those numbers look like, referred to as f-numbers:
f-2.8, f-4, f-5.6, f-8, f-11, f-16, f-22, and f-32.
Here’s a tip to help you remember the numbers, there is a pattern where the numbers, most times, double every other number.
The thing that’s confusing about these numbers is how they correspond to the size of the aperture hole. The smaller the number, the larger the hole. The larger the number, the smaller the hole.
For example in the series of numbers I showed you, f-2.8 is the largest aperture opening. F-32 is the smallest. When you look through the camera lens you are looking through the largest opening no matter what your camera is set on.
If the aperture were closed down, you wouldn’t be able compose your picture as well. So, when you push the shutter release, the aperture instantly closes down to the setting you’ve chosen and it opens back up again.
Like shutter speed, each number effects the quantity of light entering the lens by a factor of 2. In other words, f-8 lets in twice as much light as f-11. Also like shutter speed, the difference between one number and the next is called a stop.
The mechanical function of the aperture is important to understand, but lets go over how it serves as an artistic tool in your photographs.
The aperture controls how much foreground and background around your image is in focus. This is called depth of field, or it can be written DOF. It’s defined as: the area of acceptable focus.
Depth of field also relates to your f-numbers. In the f-numbers I went over, f-32 yields the largest depth of field.
You would use this if you were photographing subject where you wanted an infinite depth of field, like a foreground pasture, a mountain range, and a vast sky behind.
If you wanted to zoom in and feature just one flower in the pasture, you might use 2.8, which would blur the foreground and the mountains in the background but bring clarity and focus on the flower.
Between f-2.8 and f-32 there are varying degrees of depth of field. Exactly what those affects will be depends on the lens you are using. Experience will teach you how depth of field works with each of your lenses.
Here are a couple of examples of aperture and depth of field. This image was taken with something like f2.8 and the depth of field is shallow.
This one was taken around f-32 and everything is in focus.
And here is a portrait, using f-5.6. As a general rule, f-5.6 or f-8 tend to be the best apertures for portraits because they’ll create just the right amount of facial clarity and take the background out of focus enough to emphasize the subject.
Its important to choose your aperture setting based on what you want to be in focus in the image. You can create clear infinite vistas in a landscape image or blur out a distracting cluttered background behind a subject.
With a manual camera, this important tool will allow you to visualize how you want your final image to look, as opposed to the point-and-shoot that will decide for you. I find that creativity is best expressed by skillfully communicating with the camera’s tools.
In the words of photographer Ansel Adams, “When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence.”