focal distance
Noun: The distance from the optical center of a lens (or a curved mirror) to its focal point, where light rays parallel to the principal axis converge. It is a fundamental property determining the lens's power to bend light.
This term is used in the precise context of optics, physics, and photography to specify a key measurement of a lens system. * The focal distance of a magnifying glass determines how far you must hold it from an object to get a clear, enlarged image. * A lens with a short focal distance has strong converging power. * In the camera's specifications, the focal distance of the primary lens is 50mm.
- Effective Focal Length: In complex lens systems with multiple elements, the focal distance often refers to the effective focal length (EFL), which is the distance from the principal plane to the focal point.
- Back Focal Distance: This is a related but distinct term, referring to the distance from the last surface of a lens to its focal point.
- Focal Length: This is the most common and preferred synonym for focal distance in modern technical English.
- Focal Point (n): The point where light rays converge, not the distance to it.
- Focal Plane (n): The plane perpendicular to the axis that contains the focal point.
- Focal length
The term focal distance has a single, specific meaning in technical optics. It is not used in general or figurative contexts.
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the distance from a lens to its focus
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