In my new educational series, I will be writing informational pieces about photography to take you from the simple act of pushing a button to having a better understanding of what you are doing and how you are doing it (and hopefully giving you some grounding to expand your own photography skills). And with that, welcome to the first article:
In every photograph, there is a certain area of the image both in front of and behind the subject that appears in focus – this area defines what is referred to as the depth of field (DOF). You can have a shallow DOF (less area in focus in front of and behind the subject) or a deep DOF (more area in focus in front of and behind the subject). A shallow DOF is traditionally used in portrait photography while a deep one is employed in landscape photography.
With a basic understanding of what DOF is, it’s important to know what affects it. There are three core factors that determine DOF: the distance between the camera and the subject; the focal length of the lens; and the aperture (f-stop) setting. Let’s look at each factor individually.
Without much attention to your camera’s settings or the focal length of your lens, this factor is controlled simply by the camera’s proximity to your subject. Basically, the closer you are to your subject, the shallower your image’s DOF will be; by increasing the distance between camera and subject, you give your image a deeper DOF.
At its most basic, this factor dictates that the shorter the focal length (the wider the angle of view) of the lens (i.e. 24mm), the deeper the DOF will be. With a longer focal length (i.e. 100mm), DOF decreases (becomes more shallow). In portrait photography, telephoto lenses (i.e. 85mm or 70-200mm) are frequently used to create a shallow DOF and help separate the subject from the background. In landscape photography, the opposite is usually true: lenses with wider angles of view are typically the most popular option to bring more of the scene into focus.
I saved the most technical of the factors until the end. Before discussing how the aperture affects DOF, it’s important to first understand what the aperture is. The aperture is a hole at the rear of a lens through which light travels from the front element of the lens to the camera’s image sensor. It’s often indicated as A or Av on your camera’s dial and each aperture setting is defined as an f-stop. Common f-stop values range from f1.2 to f22, with each lens varying. Adjusting the aperture by opening or closing it will determine the depth of field in your photo. Larger/narrower f-stops (i.e. f11 or f16) will give you a deeper depth of field, bringing more of your image into focus from front to back. On the other end, a smaller/wider f-stop (i.e. f1.2 or f2.8) will give your photo a shallower DOF. By selecting the Aperture Priority mode on your camera and experimenting with f-stops similar to those above, keeping all other factors the same, you’ll be able to see how the DOF changes.
If you were to combine all of these factors into two math equations, they would probably look a little like this:
Wider Aperture + Longer Focal Length + Lesser Camera-to-Subject Distance = Shallow DOF
Narrower Aperture + Shorter Focal Length + Greater Camera-to-Subject Distance = Deeper DOF
(The image above was shot using a short focal length of 16mm and a narrow f-stop of 11, which resulted in a deep DOF.)
Thanks for reading and please leave your questions, if you have any, in the comments section below. Next time I’ll talk about bokeh, which comes from the Japanese word boke and literally translates as “blur.” Stay tuned!