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Zoom Lens > Zoom Lens Controls - Pg. 111

CHAPTER 7 What the Camera Can Do Zoom Lens Let's take a closer look at the operating features of the zoom lens. Its main advantage is that you can select or change between any focal lengths within its range without interrupting the shot. You can zoom out to get an overall view of the action and zoom in to examine details (Figures 7.32 and 7.33). The fact that in the pro- cess you are playing around with the spatial impres- sions your picture conveys is usually incidental to the convenience of getting shot variations from a camera viewpoint. In order to alter the focal length of a zoom lens, it is nec- essary to move specific lens elements to adjust the overall magnification while still maintaining sharp focus. This involves very precise mechanical readjustments. If the focal length of the lens when zoomed completely in (telephoto) is, for example, 14 times that when fully zoomed out (wide angle), it has a zoom ratio of "fourteen to one." This can be written in a number of different ways such as 143 or 14:1. With this lens, you can change the size of a subject's image size in a picture by a magnification factor of 14. You might, FIGURE 7.32 Zooming in progressively fills the screen with a smaller segment of the scene.