Articles and videos throw around the term “depth of field” quite casually, as if everyone already knows what it means. Depth of Field (DOF from here on out) could actually also be called “depth of focus” or maybe even “focus field”. DOF is all about focus, so it’s strange to me that “focus” isn’t part of the name. But whatever, it’s called DOF, and here’s what it means and how you can use it.
The simplest definition I can come up with is this:
Depth of Field is the distance between the nearest and furthest areas of a photograph that are considered to be in focus.
And that is not a very intuitive definition, I should say. And frankly, DOF is hard to describe outside of the context of whether or not a given image has a “shallow” or “deep” DOF.
An image with a Shallow Depth of Field has a very narrow zone that is in focus sharply, and focus falls off quickly the further from this zone of sharpness anything in the image is situated.
Wow, that was a mouthful, too. So let me show an actual example of a shallow DOF instead of blathering on with too many words. The gallery below shows the same subject/composition over a range of f/16 through f/1.8 using a Nikon D3300 body (my review is here) and Nikkor 35mm f/1.8G lens.
How to Control Depth of Field
There are a few factors to adjusting how deep or shallow the DOF is for a given composition, but here are the three that are the most common and easiest to control: aperture, distance to subject, and focal length of lens. And really, the last two are directly related.
The wider the aperture (smaller number f/stop), the narrower the DOF. It’s that simple. There’s some physics behind it, but I’m an English major, so somebody else will have to explain.
Distance to Subject / Background
The closer the camera is the subject, the shallower the depth of field will be. This is doubly true as the background gets further from the subject.
The longer the focal length of a lens, the shallower the depth of field at any given aperture. This is essentially the same thing as moving closer to the subject.
When to Use Shallow or Deep DOF?
For portraiture, shallow DOF is generally a requirement. Blurring the background forces a viewer to be drawn to your subject. Other sorts of still life compositions also benefit from shallow DOF. And, it also just looks cool in a lot of contexts.
Many point-n-shoot cameras and smart phone cameras are designed to optimize around a very deep DOF. This is partially because cheaper lenses tend to have smaller maximum apertures, and because a deeper DOF lessens the chance of a soft-focused image. As a result, most of the images made from these types of cameras are 100% in focus everywhere, which while useful in some ways, it certainly does not look very “artsy”.
So if you want to avoid that tourist-with-a-cheap-camera look, use a shallow(er) DOF. All the hipsters will think you are cool.
A deeper DOF is useful for landscape and architectural photography, as well as certain types of product photography. There are various reason you may want most or all of an image in focus and crisp. If so, crank down that aperture to f/8 or smaller and revel in the widespread detail.
Technical Article on Depth of Field (Wikipedia)
How to Calculate DOF Manually (DOFmaster)
Online DOF Calculator (DOFmaster)