An important technical element of storytelling in film and video is depth-of-field. Here’s a brief overview of what it is, what it does, and some basics on using it. Before I go any further, a slight disclaimer:

Depth-of-field (DOF) is comprised of three elements: aperture (iris), focal length, and sensor size.

Aperture, or iris, controls how much light hits a camera’s sensor. The more open the iris (and thus, the more light hitting the image plane or sensor), the shallower the DOF. Shallow DOF equals less that is in focus. The more closed the iris is, the broader the DOF is, thus giving crisp focus over a larger distance. In technical terms, the lower the f-stop, the shallower the DOF (f2.8 would give shallower DOF than f9.6, for instance).

Focal length, boiled down to uber-simple beginner terms (so I can understand…) is equivalent to zoom. If you’re zoomed out all the way, the angle is wider (the focal length is short), and if you’re zoomed in all the way, the angle is narrower (the focal length is long). The longer the focal length, the shallower the DOF; the shorter the focal length, the DOF is broader.

Sensor size is exactly what it sounds like. The larger the sensor size, the shallower the DOF, and the smaller the sensor size, DOF is broader. Unfortunately, this is the one element of DOF that us videographers lose out on, as most consumer and prosumer-grade cameras have fairly small sensor sizes compared to, say, a 35mm frame of film. The only solution to combat this problem and still stay digital is to pay gobs of money for a digital cinema camera (RED One, anybody?).

DOF is quite useful in storytelling, because it gives a focus to the image. It separates the subject from the background, and can be used to draw the audience’s eyes to what we want them to see.

Since those of us who use digital video are severely handicapped in this area by our small sensors, we have to employ other means of getting the kind of DOF film gets. And why do we want to get that? Because first, it is an important tool in our storytelling toolbox, and second, because it boosts production value.

So how do we go about getting good DOF using DV cameras? One solution is the 35mm adapter, which gives us the capability to put 35mm lenses on the front of our cameras. While a somewhat costly solution (one could easily spend three thousand dollars to put together a rig for one camera), it’s the best way to get the kind of DOF film gets. (For more info and an overview on adapters, check out this article by Kyle Prohaska, producer/director of the upcoming film, Standing Firm!)

But if you’re someone like me who doesn’t have a bunch of money to be buying fancy equipment, it’s nice to know that there are some other practical ways to get as good DOF as we can… And while they’re still not as good as film DOF, it helps.

It’s really as simple as knowing how to use the other two elements of DOF to your advantage (iris and focal length). Remember that the more open the iris, the shallower the DOF, and the longer the focal length, the shallower the DOF? If you keep those two things in mind, it’s easy to figure out how to get shallower depth-of-field when you need it.

Allow me to demonstrate.

Wide focal length. The iris is completely open here.

Narrow focal length. Notice the shallow DOF?

Focal length short, iris open. The focus is mostly on the crisper side throughout.

Focal length long, iris open. The background is blurred, and while it’s not as much as say, 35mm, it’s better than plain ol’ plain ol’.

So using focal length and iris, you can have a little more control of the DOF you get, even without having the advantage of a large image sensor. Of course, if you’re wanting to do more, there are two more things I can think of that one can do to get shallower DOF.

The first thing, I would heartily not recommend. When shooting my last short, Precious Treasure, I made the mistake of becoming obsessed with getting DOF without using 35mm adapters… When I figured out that if I attached my wide-angle lenses and zoomed all the way in, the DOF was shallower, I thought it was the perfect solution. But alas! It was a terrible solution, not worthy of being called a solution in the first place.

I didn’t realize until way too late that all those lenses were giving me was a nasty edge blur. Not pretty. It distracts from the shot, and I was more inclined to frame things wrong, because anything not in the center of the shot would be blurry. Thankfully, I didn’t use the lenses for too many shots…

The second solution, while painstakingly slow, can be worth it sometimes: compositing DOF. It’s not fun, and I don’t recommend doing it unless you absolutely have to. I was going to go through the majority of the shots in Precious Treasure and do this, until a friend talked me out of it (thank you, Stefan!!!). But I did do a few shots, mostly in one of the first scenes. It actually helped out in some of the shots, in my opinion.

My favorite DOF-composited shot (this is one of the ones that worked really well, I think):

At any rate, I figured that I’d just try to share what little I know thus far about depth-of-field with whoever might read this. I hope you find this helpful!

Just remember: open iris, long focal length = shallow DOF; more closed iris, short focal length = broad DOF.