Concave and convex lenses Concave and convex curvatures of lenses bend, or refract, light in opposite ways, depending on the focal length of the lens and the distance between the lens and the object, thus giving either a smaller or a larger image of the object. (more) lens formula optics Ask the Chatbot a Question More Actions Share Share Share to social media Facebook X URL https://www.britannica.com/science/lens-formula Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article.

　　External Websites Ask the Chatbot a Question Also known as: lens equation Written and fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors. The Editors of Encyclopaedia Britannica Last Updated: Mar 26, 2025 • Article History Table of Contents Table of Contents Ask the Chatbot Also called: lens equation (Show more) { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : " What is the lens formula in optics? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "The lens formula in optics is 1/u + 1/f = 1/v, relating the object distance (u), image distance (v), and focal length (f)." } } , { "@type" : "Question", "name" : " What does the thin lens approximation assume? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "The thin lens approximation assumes that the thickness of the lens is much smaller than the radius of curvature of the lens surfaces." } } , { "@type" : "Question", "name" : " How does a convex lens form a real image? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "A convex lens forms a real image when the object is farther from the lens than the focal length, causing light to converge at the focal length." } } , { "@type" : "Question", "name" : " What is the sign of the focal length for a concave lens? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "The focal length for a concave lens is negative." } } , { "@type" : "Question", "name" : " What type of images are formed by a concave lens? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "A concave lens forms virtual images, with negative image distance (v)." } } ] } Top Questions What is the lens formula in optics? The lens formula in optics is 1/u + 1/f = 1/v, relating the object distance (u), image distance (v), and focal length (f).

　　What does the thin lens approximation assume? The thin lens approximation assumes that the thickness of the lens is much smaller than the radius of curvature of the lens surfaces.

　　How does a convex lens form a real image? A convex lens forms a real image when the object is farther from the lens than the focal length, causing light to converge at the focal length.

　　What is the sign of the focal length for a concave lens? The focal length for a concave lens is negative.

　　What type of images are formed by a concave lens? A concave lens forms virtual images, with negative image distance (v).

　　lens formula, in optics, a formula relating the distance (u) of an object from a lens, the distance (v) of the object’s image from the lens, and the focal length (f) of the lens. The formula is1/u + 1/f = 1/v.The formula follows the thin lens approximation in which the thickness of the lens is much smaller than the radius of curvature of the surfaces of the lens. This form of the lens equation also follows the Cartesian sign convention in which light travels from the object in a positive direction. This means that u ...(100 of 234 words)

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