Ever wonder why your video just doesn’t have the same look and feel that you’re used to on the big screen? It might be because you’re not manipulating the depth of field.
Every lens focuses at a single point. There’s an area in front of and behind that point that’s “acceptably sharp” — not perfect focus, but in focus enough. That’s the depth of field. A deep depth of field gives you a wide area of acceptable focus (great for landscapes, for example), a shallow depth of field gives you a narrower area of acceptable focus, and incidentally, those nice blurry backgrounds we associate with a cinematic look.
There are a couple of ways to get a shallow depth of field, but first let’s be clear — just because you can shoot an image with a shallow depth of field, doesn’t mean you should. It’s great for closeups, for example, but not all of them. Depending on your story and what you’re trying to achieve, a deeper depth of field might be more appropriate. But that’s a topic for another article.
2 Ways to Achieve Shallow Depth of Field
Again, shallow depth of field isn’t the only way to get a cinematic look (nor should it be your only consideration), but it’s a good start.
- Open the aperture. Changing the size and shape of the aperture changes how the light is focused (or more accurately, the convergence of the light), narrowing or broadening the range where your image will be acceptably sharp. The wider your aperture, the more narrow this range becomes, giving you a nice, blurry background. Make sense? Here’s a video that explains depth of field pretty well.
- Use a longer lens. Longer lenses have narrower focal lengths, so it’s easier to get a blurred background just like you do with a wider aperture. Though you can get the same effect with a shorter lens by moving your camera closer to the subject, a longer lens will compress the 3D space of your image (bring the background closer) so the shallow depth of field will be more noticeable.*
There’s a big caveat here. Sensor size affects depth of field. This was largely a non-issue in the past, as everyone — especially still photographers — was shooting on pretty much the same size film. But digital sensors are different sizes. The Black Magic Cinema Camera is slightly larger than a Super 16mm and my Nikon D7000 is an APS-C sensor (between Super 35mm and a full-frame still). Smaller sensors, in general, will give you a deeper depth of field and make it a little more difficult to get a blurry background. My guess, however, is that the difference is so negligible you won’t really notice.
*Mathematically the DOF is the same for any given lens at a certain aperture when the images are cropped to keep the subject the same size, but again — without the compression of a longer lens, this isn’t as noticeable and really, not as applicable to film as it is to still photography.