Description: A lens is an optical device that, due to refraction, bends light so that it either focuses or disperses. Lenses are typically made from glass, plastic, or some other transparent material. Convex lenses focus light, drawing a parallel beam of light together to a point. Concave lenses spread a parallel beam of light so that it appears to originate from a point.

Lenses are the main components in refracting telescopes as well as binoculars. Even if an astronomical telescope is a reflecting telescope (one that uses mirrors to focus light), it is likely that the cameras and spectrographs attached to the telescope will use one or more lenses.

A massive object can be referred to as a "gravitational lens" when it induces optical distortion in the image of another background object. This distortion is due to bending of light from the background object due to the gravity of the massive foreground object; this phenomenon is referred to as gravitational lensing.

Related Terms:

• Gravitational Lens
• Optics
• Reflecting Telescope
• Refracting Telescope
• Refraction
• Spectrograph
• Mirror

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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