Perhaps there are few things as overtly confusing for most people in photography than aperture. The relationship between f/numbers, depth of field, and lens speed isn’t always clear. Honestly, understanding aperture isn’t always easy. But there’s hope! In this article, we will talk about what exactly aperture is, how it is measured, and it means for you.
What is aperture?
Aperture, at it most simple definition, is simply a hole, or an opening. That’s it; just a hole. As aperture relates to photography, it refers to the opening in the lens which allows light to pass into the camera and manifest an image.
The opening is controlled by aperture blades which are capable of expanding or contracting based on the desired aperture setting.
Aperture and depth of field
The aperture setting you choose impact a number of things concerning your photo but the two key factors which aperture influences is depth of field and lens speed. Now, there is somewhat of an over importance placed on depth of field control and aperture. While it is very true that the depth of focus is heavily influenced by the size of the aperture with a large aperture offering very shallow depth of field and a very small aperture offering a deeper focus field depth. However, the general blurring effect in the foreground and background of photos is primarily a product of distance between the subject and the focal length of the lens…before this turns in an article on focal length and bokeh, we’ll stop there. Just remember that as a guideline, large apertures produce more shallow depth of field. Here’s an example:
These chess pieces were placed at different distances from my camera.
The next three photos where shot at decreasing apertures. The increased depth of focus as the aperture size becomes smaller is evident….
Aperture and lens speed
The other thing aperture affects is lens speed. The “speed” of a lens refers to it’s ability to shoot at relatively large apertures which in turn means it’s low light performance is greatly enhanced. The lens speed has nothing to do with shutter speed or ISO, but rather is a general understanding that the wider the possible aperture of the lens, the greater its speed.
You might be thinking “But Adam, how do you measure the speed of a lens?” I thought you might ask that…well, it comes down to a ratio and the dreaded “F-number”…. But don’t worry, it’s really simple and you’re about to learn about F/numbers right now.
What is an F-Number?
The term “F-number” sounds fairly ambiguous in its own right. The term is interchangeable with “F-stop” and a few other phrases but they all describe the same thing. A F-number is a ratio between the size of the aperture opening and the focal length of the lens being used. That’s all. The confusion comes from the fact that as the F-number INCREASES the size of the aperture actually DECREASES. So the opening at F/1.4 is larger than F/2.8 and an aperture of F/16 is smaller than an aperture of F/8…see, a little confusing.
Have a look at this…as the size of the opening gets larger, the F-number get’s smaller:
The key to understanding F-numbers is to remember that on the full-stop scale, each increasing F-number let’s in half the amount of light as the one before it. This makes sense because we know that as the F-number increases the size of the aperture decreases…which naturally let’s in less light.
Key Points for Understanding Aperture
- Aperture is just a term for the variable opening in your camera lens
- F-Numbers signify the size of the aperture relative to the lens focal length
- As the F-number increases the size of the aperture opening decreases
- Lens speed refers to the maximum aperture(smallest F-number) of a lens
- Depth of field increases at smaller apertures and decreases at larger apertures
Figuring out how aperture is determined and measured can be complex and at times confusing. But that doesn’t mean that it is impossible or even difficult to wrap your mind around a few simple concepts that truly make all the difference. Don’t let it scare you! Using the information in this article will make aperture much less intimidating. A solid understanding of the basic concepts of aperture will work wonders for your photography.