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Using a positive lens of focal length f, a virtual image results when S 1 < f, the lens thus being used as a magnifying glass (rather than if S 1 ≫ f as for a camera). Using a negative lens (f < 0) with a real object (S 1 > 0) can only produce a virtual image (S 2 < 0), according to the above formula.
The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
The Gauss lens is a compound achromatic lens that uses two uncemented elements; in its most basic form, a positive meniscus lens on the object side and a negative meniscus lens on the image side.
Converging lenses have positive optical power, while diverging lenses have negative power. When a lens is immersed in a refractive medium, its optical power and focal length change. For two or more thin lenses close together, the optical power of the combined lenses is approximately equal to the sum of the optical powers of each lens: P = P 1 ...
If the vertex lies to the left of the center of curvature, the radius of curvature is positive. If the vertex lies to the right of the center of curvature, the radius of curvature is negative. Thus when viewing a biconvex lens from the side, the left surface radius of curvature is positive, and the right radius of curvature is negative.
Other lenses for the Contax included the Biotar, Biogon, Orthometar, and various Tessars and Triotars. The last important Zeiss innovation before the Second World War was the technique of applying anti-reflective coating to lens surfaces invented by Olexander Smakula in 1935. [8] A lens so treated was marked with a red "T", short for "Transparent".
The earliest double Gauss lens, patented by Alvan Graham Clark in 1888, consists of two symmetrically-arranged Gauss lenses. Each Gauss lens is a two-element achromatic lens with a positive meniscus lens on the object side and a negative meniscus lens on the image side. In Clark's symmetric arrangement, this makes four elements in four groups ...
A sign convention is used such that and (the image distance from the lens) are positive for real object and image, respectively, and negative for virtual object and images, respectively. f {\textstyle f} of a converging lens is positive while for a diverging lens it is negative.