I am going to explain two methods of controlling the portions of your shot that are in focus. This is done for artistic effect and can greatly enhance the caliber of your visual communication skills.
Usually, you think of focus as a practical thing…your shot better be in focus or your video will look terrible! Yes, that’s very true, but once you get to be a bit more advanced with your videography, you can play with focus to make your shot more meaningful or simply prettier.
There are two basic ways to do this when making video.
- Roll focus
- Depth of Field (d-o-f)
A roll focus is where you start the shot with one thing in focus, then change the focus in the middle of your shot to something else. Let’s say you want to emphasize the fact that your character is an alcoholic. You can do that visually in about 3 seconds with a good roll focus.
Start your shot with a whiskey bottle in the foreground and your character in the background, completely out of focus. Then, roll the focus so your character is in focus and the whiskey bottle is out of focus. If you time it right, the expression on your actor’s face will peak at the exact same moment the focus changes.
You will see roll focus shots used quite frequently in movies and TV shows. It is an advanced technique that is not hard at all, assuming you have manual control of your focus. Roll focus shots are a great way to say things visually instead of verbally. And that, of course, is what visual communication is all about.
The other method I am going to talk about is depth-of-field. Depth-of-field is a little more complex.
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. This baby picture of my daughter is my favorite example of depth of field. She’s now in college so I have been using this picture as an example for a long time!
See how both the foreground and the background are both out of focus? Only Ondrea is in focus. Even her shoulder is slightly out of focus. That makes her stand out.
This is an example of a very shallow depth of field. If I had taken the picture differently, both the foreground and the background would be in focus and the shot would not be nearly as good. My daughter would still be cute of course, but she would blend in with the foreground and background. I took this shot with a semi-telephoto lens in a low light situation with the f-stop opened wide. All three of those things contribute to the low depth of field.
Professional photographers often like to control depth of field in order to make the subject of the picture stand out better. Just like the baby picture 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. The exact same thing is true for a video portrait, usually called a talking head or interview. If you minimize your depth of field, you can achieve an out of focus background.
In a completely different situation, you might want to maximize depth of field. Let’s say you are videotaping a basketball game. Players are running all over the place. If you maximize your depth of field, everyone will stay in focus as they run. Without a large depth of field, the players will go in and out of focus and your video will look terrible.
Several factors affect depth of field. You, as the video photographer, can control many of these and thereby control your depth of field.
THINGS THAT AFFECT DEPTH OF FIELD
There are three main things that affect depth of field.
- The focal length of the lens being used
- The amount of light
- The f-stop setting
Probably the easiest one to control is the focal length of the lens being used. Focal length refers to whether it is a wide angle or telephoto lens. Most video cameras have a zoom lens, which is also known as a variable focal length lens. This means it has a wide angle setting, a telephoto setting and all settings in-between. As you zoom in and out, you are changing focal length.
By its very nature, a telephoto lens has a shallow depth of field. The longer the lens, the less depth of field. 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 a wide angle shot to be out of focus because the depth of field is so great. It almost does not matter where your focus is actually set, everything will be in focus.
I advise people to use this to their advantage by shooting on the wide angle portion of the lens instead of zooming in because focusing is so much easier on a wide angle setting.
As you videotape on a wide angle setting, the majority of your picture will always be in focus. Zoom in to a telephoto setting and your focus must be precise because the depth of field is so shallow.
OTHER FACTORS THAT AFFECT DEPTH OF FIELD
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.
Low light gives you a shallow depth of field. Bright light creates a 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.
At the same time, having your f-stop wide open creates a shallow depth of field. Conversely, closing your f-stop all the way down increases your depth of field.
Outside of 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. If you are videotaping outside on a bright day, adding a neutral density filter will give you some control over your depth-of-field.
Controlling depth of field and using a roll focus are both advanced techniques that can take your video production skills to a higher level. On an artistic level, both make a huge difference in the quality and meaning of your shot. However, if you are just learning, honestly I would advise you to not worry about it, although it is good to know.
Thanks for reading Video Production Tips
Internet Video Gal