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By convention, for magnifying glasses and optical microscopes, where the size of the object is a linear dimension and the apparent size is an angle, the magnification is the ratio between the apparent (angular) size as seen in the eyepiece and the angular size of the object when placed at the conventional closest distance of distinct vision: 25 ...
A Fresnel lens (/ ˈ f r eɪ n ɛ l,-n əl / FRAY-nel, -nəl; / ˈ f r ɛ n ɛ l,-əl / FREN-el, -əl; or / f r eɪ ˈ n ɛ l / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
The magnifying power V of a simple magnifying glass is related to its optical power φ by V = 0.25 m × φ + 1 {\displaystyle V=0.25\ \mathrm {m} \times \varphi +1} . This is approximately the magnification observed when a person with normal vision holds the magnifying glass close to his or her eye.
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. A magnifying glass can be used to focus light, such as to concentrate the Sun's radiation to create a hot spot at the focus for fire starting. A plastic Fresnel lens sold as a TV-screen magnifier
A Coddington magnifier is a magnifying glass consisting of a single very thick lens with a central deep groove diaphragm at the equator, thus limiting the rays to those close to the axis, which minimizes spherical aberration. This allows for greater magnification than a conventional magnifying glass, typically 10× up to 20×. Most single lens ...
Cone of light behind an achromatic doublet objective lens (A) without (red) and with (green) a Barlow lens optical element (B). The Barlow lens, named after Peter Barlow, is a diverging lens which, used in series with other optics in an optical system, increases the effective focal length of an optical system as perceived by all components that are after it in the system.
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