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Focusing > Focusing Methods - Pg. 114

PART 3 Visualizing the Story perspective. In Figure 7.36, you can actually see that the camera moved down the aisle, show- ing more information to the viewer than is possible with a zoom shot. Zooming is seldom a completely convincing substitute for moving the camera. EXTENDER LENS Some zoom lens systems include a built-in supplementary lens that is called a 2x extender. The extender can be flipped in or out of use and is available in sizes other than 2x, but that is the most common configuration. The 2x extender doubles the focal length of the lens, allowing the camera operator to zoom in much closer to the subject (Figure 7.37). There are a few drawbacks to using an extender lens: The extender lens cannot be switched in or out when shooting because it disrupts the visual image. It must be changed between shots. There can be a substantial loss of light when utiliz- ing an extender, which causes camera operators to adjust their aperture. The minimum focusing distance on the zoom lens can substantially change when switching in the extender. A zoom lens generally focuses on closer subjects when not using the extender. FIGURE 7.37 A 2x extender doubles the focal length of the zoom. (Photo courtesy of Canon) Focusing When you focus the camera, you are adjusting the lens to produce the sharpest possible image of the subject. With a prime lens, this involves altering the distance between the lens and the camera's sensor chip. With the zoom lens, focus adjustment is done by readjusting the posi- tions of internal lens elements. 114 WHY FOCUS? Simple photographic cameras do not have a focus control, yet everything in the shot looks reasonably sharp. Why do television cameras need to be continually focused? There are several reasons why fixed-focus systems do not work with television cameras: They do not provide maximum sharpness of the subject. Because the lens aperture is reduced (small stop) in order to provide a large depth of field, high light levels are needed for good images. Everything in the shot is equally sharp. That means there is no differ- ential focusing in which subjects can be made to stand out against a defocused background (Figure 7.38). The camera cannot focus on close subjects (although a supplementary lens may help). FIGURE 7.38 Focusing with a shallow depth of field will allow you to make your subject stand out against a defocused background. If needed, a camera can be put into fixed focus by using a lens with as wide an angle as possible and using the smallest possible aperture. This combination will give you the best images your camera can provide in that situation. FOCUSING METHODS Two different methods are generally used to focus the camera's lens system: Focus ring: Lens systems on handheld and lightweight cameras can be focused by turning a ring on the lens barrel, until subject details are as sharp as possible (Figure 7.39).