Focal Length: Focal length is a measure of the distance (in millimeters) from the optical center of a camera's lens to its focal point, which is located on the image sensor. Because digital cameras' focal lengths are measured differently than traditional film cameras, manufacturers usually give a '35mm equivalent' focal length in their specs. This helps 35mm film photographers get a better idea of just how wide-angle or telephoto a digital camera will be in relation to their film cam. A typical digital camera's 35mm equivalent focal length might be 28-280mm, while its actual focal length measures 4.6-46mm. The reason that a range of numbers is given here (28mm to 280mm) is due to the fact that most digital cameras have a zoom lens, which can change focal lengths. A fixed lens has only one focal length. A camera lens's focal length can tell you a lot about what kinds of pictures it will be able to take well. With a long focal length, like 280mm, a camera is better able to capture far-off subjects (such a lens is also known as 'telephoto'). With a short focal length, like 28mm, a camera can capture the scene immediately before it more completely (this kind of lens is considered 'wide-angle').

 

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Focal Length: The distance from the lens' optical center to its focal point, usually measured in millimeters. There are three conventional types of focal length: wide angle, normal, and telephoto.

Fixed Focal Length: Camera system whose lens cannot be interchanged for a lens of different focal length.

Zoom Lens (Variable Focal Length): A lens with a variable focal length, allowing the operator to shift immediately and continuously from wide angle to telephoto (or vice versa) without switching lenses.

Equivalent Focal Length: Distance in a lens between the front nodal point and the focal plane when the lens is set to focus a subject at infinity. In a telephoto lens the equivalent focal length is shorter than the . . . View Full Definition