Introduction What is photography? The history of photography What this site will do for you Light: The most important element Why light is important to a photograph The many types of light Controlling light in your pictures The camera The basic function Types of cameras Choosing the right camera Putting the image together: the Lens How the lens bends light: a tutorial A brief introduction to apertures The variety of lenses Choosing a lens Exposure: a film tutorial How film records an image Understanding film speed Print vs. Slide film Film recommendations Taking Pictures Depth-of-field Apertures and shutter speeds Composition and experimentation: the basics Metering: when you can't guess The many types of picture-taking Photography with a point-and-shoot Accessories Tripods: for when you can't stay still Lens filters Post-processing: after development Scanning photos The digital darkroom Photo and equipment storage
The Lens is considered the "eye" of a camera. It bends light so that the image will appear properly on film. Without a lens, all that would appear on the picture would be a blur.
How the lens forms an image
No matter how complex, a lens is basically a piece (or pieces) of glass or plastic that bends passing light rays, which then form an inverted image on the surface (in photography, that would be the film). Moving the lens farther or closer from the film would sharpen or blur an area of the image. This is called focusing. The lens can also permit the amount of light that reaches the film, by the help of an aperture diaphragm. When the diaphragm widens, more light passes thorough the lens. When it closes, less light passes through. A lens can be as simple as a magnifying glass to as complex as an observatory telescope, but they all serve the same function: to form an image.
Elements: what the lens is made up of.
As said before, a lens can be simple or very complex. The complexity of a lens is mainly determined by the number of elements, or single pieces of glass, that make up a lens. A simple magnifying glass usually has one piece of glass on it, so that would mean it has only one element. In camera lenses, however, it is typical to have 6-8 elements. All of these make up one lens.