Lens aperture terminology, an introduction: A simple explanation of what lens apertures are and how where the f/stop numbering system came from.
A Lens Aperture Primer: Everything You Need to Know About f/stops
In some situations you'll want to create a lot of near-to-far sharpness (called "depth of field") and that requires using a smaller aperture. You'll learn all about aperture size in this tutorial.
In other situations, of course, you'll want to limit depth of field to a very shallow area. In this photo of a young girl blowing bubbles, I intentionally chose a large aperture to restrict focus to her face.
Lens Apertures: An Introduction
If you're going to truly understand how your camera controls exposure, it's important that you understand the two primary physical controls of how light gets into your camera: lens aperture and shutter speed. The two (along with the ISO speed you've set on your camera) have total and exclusive control over how light enters your camera, reaches your light-sensitive sensor and records the exposure. In this tutorial we'll take a look at lens apertures or, as they're usually referred to in photo shorthand: f/stops.
The primary function of the lens aperture is to let light into your camera. No aperture, no light. The ability to adjust aperture size gives you profound and precise control over exactly how much light reaches your camera's sensor. If that were all there were to the aperture story, of course, this would be a very short tutorial. But there is, of course, more to the story--and this tutorial is where the fun and sexy part of apertures comes to life.
One of the by-products of having an adjustable aperture is that, because of the physics of optics, a very interesting thing happens as you change he aperture size: the amount of near-to-far focus (also called depth of field) changes. That small fact is one of the most creative and interesting tools that you have access to as a photographer. The ability to shift what is and what isn't in focus, beyond the actual point of sharp focus, gives you extraordinary control over how viewers interpret your subjects. You can, for example, toss backgrounds totally out of focus (fun to use in portraits) or pull everything in a scene into sharp focus (something you'll use often in landscapes).
Before I begin to explain the fun and magic of depth of field (that's coming in a separate tutorial) though, I'm going to first present a gathering of technical concepts and definitions closely related to apertures. There really aren't that many technical things to remember about apertures, but understanding the concepts and being familiar with the lingo will be quite useful. One of the great things about learning how apertures work and understanding the terminology, especially if you own a DSLR, is that this information will help you when it comes to shopping for lenses. Much of what makes lenses expensive (or inexpensive) is related to their aperture system.
Here's something else you might find interesting: Lighting and subject aside, the thing I think about most when I'm taking pictures is aperture. Knowing what will or won't be in focus is very important to me when I'm shooting and so are things like the brightness of the viewfinder (which you'll see shortly is related to aperture size). In fact, if you were to tap me on the shoulder when I was about to shoot a picture (and I'll discourage that idea right here and now) you would likely interrupt just one thought: Am I using the right aperture?
