In photography, aperture is the size of the opening in a lens through which light passes to reach the sensor of the camera body. Aperture is expressed in f-numbers or "f-stops" such as f/1.2 or f/22. Smaller numbers, like f/1.2, indicate larger apertures, while larger numbers, such as f/22 indicate smaller apertures. The aperture not only controls the amount of light that enters the camera, but it also controls the depth-of-field. Wide apertures, like f/1.2, yield a more shallow depth-of-field, while small apertures, like f/22, yield a greater depth-of-field.
technical explanation of aperture f-number
Have you ever wondered why the numbers of an aperture seem to get "bigger" as the aperture itself gets physically "smaller"?
That's because the aperture is a fraction, and the number you're used to seeing is the denominator. f/2 means, something divided by 2. That something, the "f", is the focal length of the lens!
But, what's the whole point of this equation? It calculates the diameter of the iris (opening) of the aperture. So, for example, a 50mm f/2 lens would have a 25mm aperture at f/2. If you stopped down to f/4, the diameter of your aperture would be 50mm / 4, or 12.5mm.
Even once you understand the numbers, just talking about dialing your aperture "up" or "down" can seem confusing, because there are so many different ways to reference it. So, here is a quick, categorized list of the two "directions" you can dial your aperture:
Dialing a BRIGHTER exposure with your aperture may be referred to as:
- Lower Number
Dialing a DARKER exposure with your aperture may be referred to as:
- Higher Number
Artistic effects of different apertures
For most photographers, all that really matters is: what can you do with your aperture to help create a great photograph?
Aside from making your exposure brighter or darker, which can be an artistic tool by itself, using a wide, fast aperture will give you shallow depth of field, a blurry background, whereas using a tight, slow aperture will give you more depth of field, or less background blur, and more of your image in focus.
Put another way, at a fast aperture like f/1.4 or f/2, your lens' focus will be very selective, whereas at f/16 or f/22, your lens' focus may include everything from the nearest subject to the horizon.
Oh, and one other thing: stopping your aperture down can make any pin-point type of light into a beautiful sunstar! Contrary to popular belief, however, you don't have to go all the way to f/22 to achieve good sunstars. All you have to do is stop your aperture down 3-4 stops. Try f/8 or f/11 for starters. Be sure to share your images with us!