Lens--Lilia

Lens

The lens is one of the most vital parts of a camera. The light enters through the lens, and this is where the photo process begins. Lenses can be either fixed permanently to the body or interchangeable. They can also vary in focal length, aperture, and other details.

Source: http://www.steves-digicams.com/knowledge-center/how-tos/photography-tips/10-basic-camera-parts.html#b