Exposure Part 1 - Aperture

In this post, we'll talk more in depth about one of the three settings that controls exposure: aperture.

"Aperture" refers to the size of the opening inside the lens that admits light into the camera. More specifically, the aperture is a hole in a piece of opaque material that "stops" light. This piece of light-stopping material is called the "diaphragm"; the hole itself is the aperture. If you're getting too caught up in the terms, just think of your eye. Your pupil is the hole in your eye that allows light in, and this is just like the aperture in a camera. Your iris is like the diaphragm, it controls the size of your pupil and can get bigger to let more light in, or smaller to admit less light.

To use another example, think of a fire hose compared to a garden hose. The bigger opening in the fire hose allows more water to pass through in a given amount of time. If I turn on a firehouse for 10 seconds, I'm going to get a lot more water than if I turned on a garden hose for that long. Although this isn't a perfect metaphor (you can change the speed of water, while the speed of light is always the same), the basic principle is the same for the aperture in a camera. Big hole, more light. Little hole, less light. Nothing to it.

When we talk about aperture settings in photography, we use a weird unit of measure: "f-stops". When written, an aperture setting appears as the letter "f" followed by a number. Sometimes there is a slash between the "f" and the number, which I tend to use but is totally optional (example: f/11 and f11 are both fine). If you read this out loud, you'd say "f eleven".

The only weird part about aperture settings is how random the numbers seem. Here's a progression of  aperture settings in "full" stops, then I'll explain a bit more below:

f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16

The lower the number, the wider the aperture, that is, the bigger the hole. f/1.4 is a very large aperture, f/16 is a small aperture. So what's the difference between these settings? If I change the aperture setting on my camera from f/1.4 to f/2, this halves the size of the aperture, letting in only half as much light as before. If I go back to f/1.4, I am now letting in twice as much light as I was at f/2. This halving or doubling is a "full stop".

To wrap things up, let's discuss how aperture ties in to exposure. In order to get a proper exposure, we want to let the "correct" amount of light into the camera, depending on how dark or bright our environment is. One way to control this is to adjust the aperture. Outdoors in direct sunlight, I may select a very small aperture such as f/16. Inside my house I would probably use a larger aperture like f/1.4.

At this point in the discussion, there doesn't seem to be much reason to choose one aperture over another. However, aperture affects more than exposure. Later in the blog we'll talk about how aperture affects sharpness and depth-of-field (i.e. how much of an image is in focus at one time). Also, your choice of aperture will affect the other exposure settings you choose when you set your shutter speed and ISO.

For now, here's the big things to remember:

1. Big, wide aperture is a large hole that admits more light. A small, narrow aperture is a tiny hole that only admits a small amount of light.
2. Low f-number = big hole. f/1.4 is a very wide aperture. Conversely, a high f-number means a small hole. f/16 is a tiny pinprick.
3. Aperture will affect the appearance of your images and impact other camera settings in important ways which we will talk about in-depth later on. Selecting an aperture setting can be either a creative decision or a practical one, and this will be a constant consideration as you begin exploring photography.