Aspects of Camera Lenses: Optical Centre
Camera lenses, like all lenses, possess an optical center. On simple lenses, like a single, curved piece of glass, light bends as it travels slower through the transparent material. A viewer behind the lens will then see objects in front of the lens as distorted. However, there is a spot directly in the middle of the lens where light strikes the lens at 90 degrees. Here, although the light is slowed, there is no bending because the light outside and the light inside the lens form a perfectly straight line.
Camera lenses are formed from multiple simple lenses. These pieces of glass may not be symmetrical, identical or even similar to one another. However, they come together to form what is functionally the same as a simple lens.
Significance of the Optical Center
The concept of the optical center comes in play with zoom lenses. If a photographer puts an object in the center of the frame and then adjusts the zoom, the object stays approximately the same size while everything around the object changes size. If the object is large enough, then only the center spot on the object stays the same, while everything else changes size, creating the illusion of moving farther or closer to the object. This process is referred to as zooming in or zooming out.