Depth of field: What is it and is it useful to me?In my article on how to make video look like film I mention "Depth of Field". It's a complex sounding term which many people struggle to come to grips with.Lorraine Grula from Videoproductiontips.com has put together an excellent little article explaining more about depth of field and how to work with it in video. Thanks to Lorraine for her excellent work here. Pop over to her site for more tutorials, editorials and videos! Depth of Field Depth of field is a photographic term that refers to the amount of the picture that is in focus. Depth of field is not fixed for any particular shot; it is controllable within limits if you know how. Professional photographers often like to control depth of field in order to make the subject of the picture stand out better. For example, any portrait is probably better if the background is out of focus. An out-of-focus background does not compete with your subject, so it creates a better portrait. If you minimize your depth of field, you can achieve an out of focus background. On the other hand, you might want to maximize depth of field so more of the picture is in focus. Let’s say you are videotaping a soccer game. Players are running to and fro rapidly. If you maximize your depth of field, players will stay in focus as they run. Without a large depth of field, the players will go in and out of focus as they run further away or closer to the camera. Several factors affect depth of field. You, as the photographer, can control many of these and thereby control your depth of field. First, let’s start with a more in-depth definition of depth of field. Focus is measured from the distance of the camera to the subject. If you look at the focusing ring of any camera, it is marked in feet/inches and or meters/millimeters. To focus, you turn the ring to the correct measurement of how far the subject is from the camera. Then, there will be an area in front of, and behind the subject that is also in focus. It is that in-focus area that is your depth of field. THINGS THAT AFFECT DEPTH OF FIELD There are three main things that affect depth of field.
Probably the easiest thing to control is the focal length of the lens being used. Most video cameras have a zoom lens, which is also known as a variable focal length lens. A zoom lens has both a wide angle setting, a telephoto setting and all settings in-between. A telephoto lens has a shallow depth of field. The longer the lens, the less depth of field. So a 400 mm lens has virtually no depth of field whereas a modest telephoto, like an 80 mm, will have a slight depth of field. A wide angle lens has a deep depth of field. The wider the lens, the larger the depth of field. An extreme wide angle lens has an infinite depth of field. It is almost impossible for any part of an extreme wide angle shot to be out of focus because the depth of field is so great. This means if you are videotaping with your wide angle setting, the majority of your picture will be in focus. If you are using a telephoto setting, your focus must be precise because the depth of field is so shallow. So depending on whether you want a deep depth of field or a shallow one, either walk up close to your subject and shoot wide or put it on a tripod and shoot from a distance, zoomed all the way in. The amount of light and your f-stop setting also affect depth of field. Now obviously, your f-stop setting is related to the amount of light you have. But both things affect depth of field on their own. In low light you have a shallow d-o-f, and in bright light you have deep d-o-f. If you are videotaping in a controlled environment, add more light for a greater depth of field and darken it up for a shallow one. If your f-stop is wide open, your depth of field will be less. Stopped all the way down, your depth of field increases. So an extreme telephoto lens in a dark environment opened all the way up will have virtually no depth of field. Getting your subject in focus would be a challenge in this situation. On the other hand, videotaping with a wide angle lens on a bright day stopped all the way down will have virtually infinite focus. Besides controlling the amount of actual light, you can add a neutral density filter to make the camera think there is less light. (A neutral density filter decreases the amount of light coming into your camera but it does not change the color temperature of your light). Some high priced video cameras will have a built in neutral density filter. For lesser priced cameras, you would need to screw one on to the front of the lens. Controlling depth of field is an advanced technique. On an artistic level, depth of field can make a huge difference in the quality and meaning of your shot. Return from Depth of field to Technical editing
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