Winn L. Rosch Hardware Bible, Sixth Edition

Zoom

Technically speaking, a zoom lens is one that allows you to change its focal length within a given range. For most people, however, the results of the zooming process are more important. Zooming lets you change the size of the image in your viewfinder and in your files. You zoom in to make things bigger, as if you had stepped closer to whatever you're photographing. Zooming out makes things smaller so you can fit more of your subject into the frame. Zooming also has aesthetic effects, such as changing the depth of field and compressing distance.

Optical Zooming

The classic zoom is optical. The lens creates the entire zoom effect by changing the path light beams take through the lens. The optical principle is actually simple. A zoom lens ...