The Hypnotic Effect of Depth of Field

mainSo you have questions, problems. Do not fear. First, you must gaze...deep..., deeper into my lens.

Things are getting blurry, you are having trouble focusing. Never fear you are safe. You have merely dove deeper into...the Depth of Field.

Is Depth of Field a mystery to you? Are you hypnotized by the beauty of the softness but just seem to drift in and out of it from time to time not knowing how or why you got there? If so, you are very confused and I am here to help.

Depth of field is a very simple process to achieve. You could say it's as easy as counting backwards. There are basically only three things you must do. But you must also remember that each one of those things affects the other. Do all three every time and you will have your viewing audience in a trance.

Zooooooom
 
When ever you shoot, shoot as zoomed in as possible. The longer your lens, the higher the millimeter, the tighter the shot, and the softer the background will be. If youra framing seems too close, back away from the subject. If your shot becomes too wide, try zooming in as you back away to maintain your framing. There may need to be a compromise here, considering your location. If you are inside, sooner or later you will run into a wall. If that is the case, consider shooting diagonally across the room. If you are doing an interview and your guest seems too far away from your interviewer, try moving the interviewer closer to the guest but keep them just outside of the field of view. The camera may seem a bit out of place but if shallow depth of field is what you want, back is better. If you are outside doing dramatic or cinematic scenes then shooting long on the lens probably won't be an issue, however holding focus as your talent moves will be. When you are working with a short depth of field, moving subjects become a real challenge. Be sure to measure from the sensor plane to the points at which your talent will land. You can also try using a laser measuring device. It's fast and can even be done while the shot is happening if the framing is not too wide. Otherwise you can always reverse the process by switching to a wider lens and moving in.

Open your Mind
 
bAnd your iris. Set your aperture/iris/F-stop to as open as you can get it, (a.k.a. the smallest number possible.) The wider open you set your iris, the blurrier the background will get. Think of it this way. The smaller the pixels, the more of them you can fit on a chip and the sharper the image is. Like in HD, 1080 is sharper than 720. If you shut your F-stop down, the opening gets smaller, hence letting in tiny beams of light. So conversely, opening up and therefore making the iris larger, makes the image softer.

Scientifically we use a much more detailed explanation of this, called "Circles of Confusion" and I would go into all that explanation but shall we say..., it's a little confusing. Well that's all great if you have a manual iris, but what about if your camera only has an auto iris. If that is the case, then try lighting your subject a little darker or engaging the ND (Neutral Density) filters on your camera. This will open it as well.

TIP: Even if you have a manual iris using an ND filter helps a lot. You won't need much. If you don't have one on your camera or own one, I would suggest getting a set. The Tiffen Company is one that makes a wide array of neutral density filters in all shapes and sizes. They also sell sets of ND kits that have a ND3, ND6, and ND9 so it will cover all your bases weather you are in or outdoors. Remember, open is better.

Push em' Back, Push em' Back, Way Back
 
Away from the background that is. The farther away from the background your subject is positioned the better. This gives you lots of space for the focus to fall off. Byc far, this section of learning about depth of field is the third and hardest part. You will need to concentrate about what I am about to say. Listen to my words. The hardest part of getting good depth of field is positioning, because the area of focus moves. That's right. It grows and shrinks depending on the factors we have discussed so far. Think of the area of things in focus, like the musical instrument, the accordion.

When you use a wide angle lens the accordion is pulled wide apart. Increasing what is in focus. As you zoom in, the area of focus decreases or crushes just as if you were squeezing the accordion. Also too if you open your iris, it has the same effect. By doing both the iris and zoom at the same time you magnify it even more making the area of what is in focus, very small. One thing you must be careful of however is that when you do both of these things, it is very possible that your subject will move out of the area that is in focus.

Think of it as if the musician with the accordion walked away from the camera, taking with him his accordion, hence what is in focus. If he has expanded his arms really wide, your focus may still be clear. However if he has crushed the accordion, your subject may no longer be in the area that is in focus. So what you will have to do is move your subject or your camera to place them back within the musicians arms reach (i.e. the depth of field). Sometimes depth of field can be as little as a few inches, so place carefully.

Know Cheating

There is another way to cheat and get a short depth of field, if you don't have the room. You can place a stretched single net, a few feet directly behind your subject. This will make the focus of the background drop immediately to a nice soft look. A "net", sometimes also called a "scrim", is a professional fabric that comes in a wide array of sizes and densities. It is typically used in lighting to decrease the amount of light without softening it or changing its color temperature. However this focus trick is another way to use it.

The net is very similar to the black fabric used on screen doors and windows. In fact I have even seen screen material used in place of nets. The pro versions, however, are much more versatile. They come in single, double, and triple layers and can be as large a 20'x40' or more. A company called Chimera has a portable 6'x6' aluminum frame that breaks down for travel called a Panel Frame and a single layer scrim that will work perfectly for a single person interview. Don't forget, you will need it to be placed a few feet in behind the subject and then stretch it tight over the frame. Also your shot must be small enough so as not to see it. Otherwise you will give the trick away.

Now it is time for you to return to the real world. On the count of three you will awaken. You will have learned much. 3...2...,1..., open yours eyes. Are things still blurry? Good! Now you know you have good depth of field.


Michael Reff is Director of Photography at Turner Broadcasting.