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.

 

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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

Afocal Lens: Lens attachment that alters the focal length of the camera lens without disturbing the distance between the lens and the film plane.

Focal Plane: The plane within a film camera where the light strikes the film.

Focal Plane Shutter: Shutter which lies just in front of the focal plane. Light sensitive film positioned at the focal plane is progressively exposed as the shutter blinds move across it.

Focal Point: In a camera lens, that spot where the light rays, bent by the lens, converge before expanding again and striking the film or electronic pickup at the focal plane.

Crown Lengthening: A surgical procedure exposing more tooth for restorative purposes.

Arms-Length Transactions: Business dealings between independent and rational parties who are looking out for their own interests.