optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

, a Mangin mirror is a negative meniscus lens with the reflective surface on the rear side of the glass forming a

curved mirror A curved mirror is a mirror with a curved reflecting surface. The surface may be either ''convex'' (bulging outward) or ''concave'' (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are ...

that reflects light without

spherical aberration In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. Lenses and curved mirrors are prime examples, because this shape is easier to manufacture. Light rays that strik ...

if certain conditions are met. This reflector was invented in 1876 by a French officer Alphonse Mangin as an improved catadioptric reflector for

search light A searchlight (or spotlight) is an apparatus that combines an extremely bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular dir ...

s and is also used in other optical devices.

Description

The Mangin mirror's construction consists of a concave ( negative meniscus) lens made of crown glass with spherical surfaces of different radii with the reflective coating on the shallower rear surface. The

normally produced by the simple spherical mirror surface is canceled out by the opposite spherical aberration produced by the light traveling through the negative lens. Since light passes through the glass twice, the overall system acts like a

triplet lens A triplet lens is a compound lens consisting of three single lenses. The triplet design is the simplest to give the required number of degrees of freedom to allow the lens designer to overcome all Seidel aberrations. The three lenses may be cem ...

. The Mangin mirror was invented in 1876 by a French military engineer named Colonel Alphonse Mangin as a substitute for the more difficult to manufacture parabolic reflecting mirror for use in searchlights. Since the catadioptric design eliminated most of the off-axis aberration found in parabolic mirrors, Mangin mirrors had the added advantage of producing a nearly true parallel beam of light. They saw use in the late 19th century as reflectors for

naval A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. It inclu ...

search lights. Its use in military applications was limited, since glass reflectors of any kind were thought to be too fragile and susceptible to enemy gunfire.

Applications

Mangin mirrors are used in illumination and image forming optics such as

headlamp A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term for ...

s, aircraft gunsights and head-mounted displays. Many catadioptric telescopes use negative lenses with a reflective coating on the back surface that are referred to as "Mangin mirrors", although they are not single-element objectives like the original Mangin, and some, like the Hamiltonian telescope, predate the Mangin's invention by over 60 years. Catadioptric mirrors similar to the Mangin are found in the Klevtsov–Cassegrain, Argunov–Cassegrain telescopes, and Ludwig Schupmann's Schupmann medial telescope. They are also used in compact catadioptric photographic lens designs that save on mass since aberration can be corrected by the mirror, itself. Mangin mirrors are also used in null correctors, which are used to fabricate large aspheric mirrors. p. 168.

Notes

{{reflist

External links

Applications of Mangin mirrors
Mirrors