How Does a Camera Lens Work?
The Camera's Eye
A camera lens is the "eye" of a camera, allowing it to see the outside world. It also works a lot like a human eye, in that light passes through the lens and is focused on the film or image sensor of a digital camera. This light carries the images that both you and camera see.
A lens has several elements inside a metal barrel. Each element is actually a simple lens itself--a piece of carefully shaped and polished glass. The glass elements in the lens are what focuses the image for the film or sensor.
Focal Length
Lens have different focal lengths, the distance between the lens and the film or image sensor. This distance is measured in millimeters. To focus on something close, the lens is moved farther from the film or sensor. This is why a lens moves back and forth as it focuses.
A standard lens has a focal length of 50 mm, which closely approximates what the human eye sees. This is a "fixed" lens, with no zoom.
A zoom lens can vary it s focal length. A common zoom has a focal length of 28 mm or 80 mm. It is used to bring a subject closer (like binoculars) without the photographer moving.
A wide angle lens is also fixed, but typically has a focal length of 28 mm. A wide angle lens enlarges the image, and are useful for portrait photography. You can focus tightly on the subject with a wide angle lens while remains a respectful distance away (and out of the way of the studio lights).
SLR, LCD or Point and Shoot?
A SLR (Single Lens Reflex) lens allows the photographer to look directly through the lens and see exactly what the camera sees. In film days, this was the lens of choice for professional photographers, and is still popular with today's pros.
A digital camera with an LCD screen shows the photographer what the sensor is seeing through the lens.
A "point and shoot" camera generally uses a separate lens for the photographer to look through. On disposable film cameras, this is just a window to line up the shot. Most good digital "point and shoot" camera's have both a separate viewing lens and a LCD screen.
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