Techniques For Video

 

Wide Camera and Tight Camera

 

Focus, DOF, Aperture, Sensor Size

Hyperfocal Distance, Near Distance and Far Distance

The point you focus on is called the Hyperfocal distance, The Hyperfocal Distance is the first distance in front of the lens which will be in focus all the way out to infinity. The wider the lens setting the closer to the lens is this starting point.

Depth of Field (DOF)

This is the distance range in front of the lens which is acceptably sharp to be considered in focus. The focus starts at the Near Distance point and goes to the Far Distance. The point at which your camera is focused is about 1/3- of the way in from the Near Distance point, leaving about 2/3 of the Near-to-Far distance remaining.

Concepts	Formulae
Hyperfocal distance ( H )
Near distance - acceptable sharpness ( Dn )
Far distance - acceptable sharpness ( Df )
Depth of Field Increases When Focal length decreases (i.e. wide angle) Distance increases F-Number increases (iris becomes smaller) Decreases When    Focal length increases (i.e. telephoto) Distance decreases - gets closer F-Number decreases (iris becomes larger)	H is the hyperfocal distance, mm f is the lens focal length, mm s is the focus distance Dn is the near distance for acceptable sharpness Df is the far distance for acceptable sharpness N is the f-number c is the circle of confusion, mm

F-Stop (Aperture or Iris Opening)

An F-Stop refers to the diameter of the iris through which light passes. The F-Number is the number of times the diameter of the iris will go into the focal length of the lens. F/16 means that the diameter of the lens is 1/16-th of the focal length of the lens. F/2 means the diameter of the iris is 1/2 the focal length of the lens.

That is why F/2 is so much larger than f/16. When you see an F-Number think of it as a fraction.

Depth of Field

Factors Affecting Depth of Field

 

 

Using Autofocus

Autofocus is a love/hate thing with me. There are times I really need it and other times I curse it. Still, because most video cameras you will use do not have distance settings on the lens you are pretty much stuck with using autofocus at least intermittently to set the focus.

 

When the lights go out and you are on autofocus.

As fast as you can zoom out, all the way (wide). This won't put you in focus as far as the hyperfocal spot goes but it will give you a better depth of field, minimizing the the bloom of an unfocused lens. When a small-size chip camera is zoomed out as far as it can go, the depth of the area in front of the camera is increased dramatically. When the lights are brought up your frame will most likely be in focus. Then you can zoom in to the subject and the camera will follow the focus all the way in.

If you are still zoomed out when the lights return the chances are that your image will be a big moving soft blob or blobs and will refuse for (what seems) the longest time to find a focus.

To avoid this as much as possible. Use autofocus while the lights are still bright. When you are zoomed as far in to the action as you want and when the dancers are at a typical distance from camera to stage, hit the button to toggle on manual zoom. Now, when the lights go off you are pre-focused for the next piece. Just pre-point the camera to the stage location where the dancer or dancers will be when the lights come up.