Definition

Noun: A Fresnel lens is a type of optical lens composed of a series of concentric, thin, annular sections. This design allows for the construction of a large-aperture and short-focal-length lens that is much thinner and lighter than a conventional solid lens of comparable power.

Usage

The term "Fresnel lens" is used to describe this specific optical component. It is a compound noun, always used as a singular noun, though it can be pluralized as "Fresnel lenses."

Examples

• The Fresnel lens in the lighthouse magnified the light beam, making it visible from many miles away.
• Large-screen projection televisions often use a Fresnel lens to focus the image.
• The engineer replaced the damaged Fresnel lens on the traffic signal.
• Modern Fresnel lenses are made from molded plastic, making them inexpensive to produce.

Advanced Usage

• The design principle is based on the Fresnel zone concept in wave optics, which is named after the physicist Augustin-Jean Fresnel. The lens effectively collapses the volume of a standard convex lens into a flat profile by breaking the continuous surface into discrete rings, each with the same angle of refraction as the corresponding section of the original thick lens.

Variants and Related Words

• Fresnel (proper noun): The surname of the French physicist Augustin-Jean Fresnel, after whom the lens is named. It is often used attributively (e.g., Fresnel principle, Fresnel diffraction).
• Compound Lens (noun): A general term for a lens system made from multiple simple lenses. A Fresnel lens is a specific type of compound lens.
• Flat Lens (noun): A broad category that includes Fresnel lenses and other thin optical devices.

Synonyms

• Stepped Lens: A descriptive synonym highlighting the lens's terraced, concentric ring structure.
• Zone Plate: A related optical device that operates on a similar principle of concentric rings but uses diffraction rather than refraction. It is not a perfect synonym but is conceptually linked.

Related Phrases and Terms

• Fresnel Number: A dimensionless number used in optics to characterize Fresnel diffraction.
• Focal Length: The distance over which collimated rays are brought to a focus, a key property of a Fresnel lens.
• Collimate: To make rays of light parallel. Fresnel lenses are often used in collimation or focusing applications.

Noun

1. lens composed of a number of small lenses arranged to make a lightweight lens of large diameter and short focal length