Depth of field

So what is depth of field? And why is it so important? You may have read something about this, or perhaps this is completely new ground for you. But you may have seen in movies you've watched that often the back- or foreground is blurry.
This is because the focus of the lens is on a different part of the shot. It's an effect that is created by the lens, and used extensively in movies. Watch any Oscar winning movie, and you'll see that in most of the shots not everything is in focus.
Now there are two main reasons why filmmakers want to have this blurriness in their shots. First of all because it looks more natural. You may have noticed that if you look very close at your fingers with your own eyes, that the background gets blurry. This happens because our own eyes can focus on only one point at the time. The exact same things happens with the lens on a camera. Therefore your lens behaves much more like your own eyes, and gives everything a much more natural look.

Changing the focus will change where your audience is looking

The second reason why filmmakers use this, is because it gives them the power to control where the audience is looking. You might for instance have a very busy shot, with lots of action happening in the background, but you want to show what's happening to the person in the foreground. If you focus with your lens on the character in the foreground, the background, will go blurry, and the audience's attention will automatically go to the character in focus. You can even use the focus of your lens as a storytelling tool.

Let's say for instance that you have place a character in the background, and keep the focus on the character, and change the focus to the foreground to reveal a key when he looks up to it. In this example, the character, doesn't even need to talk. Because without saying a word, we made it perfectly clear to the audience that he was looking for the key. This kind of effect is called a focus pull. Focus pulling is a frequently used filmtechnique to reveal or hide certain things in your movie. You can also use a focus pull to switch between talking characters depending on who is talking.

So once you understand how you can use the depth of field in your storytelling, now we can begin to focus on the technical side. Because how can you create this effect? Which camera do you use? And what do you need to look for in camera's and lenses?

F-stops on a lens

First of all it's important to understand that it's the lens that creates the effect. And the basic rule  here is, that the more light falls into your lens, the shallower depth of field you will have. So you want to have a lens that allows you to let as much light in the lens as possible, giving as much exposure as possible, in order to create a nice shallow depth of field. Now don't make the mistake in thinking that if you put the ISO (or ASA for filmcamera's) higher your lens will get in more light, because it doesn't. The ISO only over-exposes your footage after it passes the lens, so it will not actually give you a shallow depth of field. The only thing the ISO will do is over-expose your image, and therefore create a grainer image, which can look bad if you put the ISO too high.
What you need to so in order to let as much light in the lens as possible, the lens need to open as much as possible. Basically see your lens as your eye. If you close your eyes, no light is comming in, and you can't see anything. If you open up your eyes completely, you can let all te light in the room fall into your eyes, and you'll have maximum exposure. The same things goed for a lens. The more the lens opens up, the more light it lets in. How much a lens opens up to let light fall into a lens is called an F-stop. The F-stop controls how much light the lens let's into the camera, and therefore the exposure.

Higher ISO just means more grain

So we need a couple of things to create this effect when we're looking for a camera and lens which can achieve this. First of all we need to have a camera and a lens that allows you to control the F-stop. Most digital camera's won't allow this, except for DSLR camera's, the RED One camera and analogue camera's like 8mm, 16mm and 35 mm camera's. Obviously most of them are quite expensive, except for the DSLR camera's which can range in price from between 400 euro's to 5000 euro's max. Of course it's your pick to choose which camera you want, but remind yourself that a cheaper camera will also result in a smaller sensor in the camera, resulting in less quality (although the qualilty of any DSLR camera is still better than most digital camera's).

Now you can choose to buy a DSLR with a packaged zoom-lens, which is a nice starters-kit, but the zoom lens is not the kind of lens you want to work with when you're trying to do some nice shallow depth of field shots. That is because most of these lenses will begin with an F-stop of 3.5 going up to 22. To create a nice shallow depth of field you want to keep your F-stop below 4. This will mean that the zoom-lens will probably only give you a low F-stop when you're using wide shots, but when you zoom in the F-stop will go up, and you'll loose that shallow depth of field effect.
The best thing you can do is buy (or rent) a couple of prime lenses, lenses with a fixed size, that have a very low F-stop. These lenses will range in price going up from 99 euro's, and of course the question is how many lenses you want to buy versus how many lenses you need. Buying 10 lenses could become an expensive investment, so it's better to think about which lenses you need, using your storyboards to figure that out, and than buy stratergically lenses which you absolutely require.

4 different 50mm Canon lenses with 4 different F-stops

Remember with buying lenses that all of the lens sizes, in terms of perspective, are named in mm's. Which means a lower number of mm's is a wider shot, and a higher number of mm's is a tighter shot (like a close-up). Look carefully at the lenses you might want to buy at what mm they are, to match the type of shots you want (wide-shots, medium and close-ups), and combine that with looking for a lens with a low F-stop and of course something that fits within your budget.
You can also think about renting lenses for your movie, to spare yourself the costs of buying lenses you might not use every day. A good thing would be though to have a DSLR of your own with at least one prime-lens, so at least you have some experience with your camera before you go and shoot with it.

I hope this explains a lot to you, and if you do have any question, feel free to email them to me on: basilios85@gmail.com. Good luck and happy shooting!