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A triplet lens is a 
The three lenses may be cemented together, as in the Steinheil triplet (optimized for finite conjugate ratio) or the Hastings triplet (optimized for infinite conjugate ratio). Or a triplet may be designed with three spaced glasses, as in the
compound lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
consisting of three single lenses
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
. The triplet design is the simplest to give the required number of degrees of freedom
In many scientific fields, the degrees of freedom of a system is the number of parameters of the system that may vary independently. For example, a point in the plane has two degrees of freedom for translation: its two coordinates; a non-infinite ...
to allow the lens designer to overcome all Seidel aberration
In optics, aberration is a property of optical systems, such as lenses and mirrors, that causes the ''image'' created by the optical system to not be a faithful reproduction of the ''object'' being observed. Aberrations cause the image formed by ...
s.
The three lenses may be cemented together, as in the Steinheil triplet (optimized for finite conjugate ratio) or the Hastings triplet (optimized for infinite conjugate ratio). Or a triplet may be designed with three spaced glasses, as in the Cooke triplet
The ''Cooke triplet'' is a photographic lens designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York. It was the first lens system that allowed the elimination of most of the optical distort ...
. The former has the advantage of higher optical throughput due to fewer air-glass interfaces, but the latter provides greater flexibility in aberration control, as the internal surfaces are not confined to have the same radii of curvature.
Jewellers' loupe
A loupe ( ) is a simple, small magnification device used to see small details more closely. They generally have higher magnification than a magnifying glass, and are designed to be held or worn close to the eye. A loupe does not have an attached ...
s typically use a triplet lens.
See also
*Doublet (lens)
In optics, a doublet is a type of lens made up of two simple lenses paired together. Such an arrangement allows more optical surfaces, thicknesses, and formulations, especially as the space between lenses may be considered an "element". With a ...
*Achromatic lens
An achromatic lens or achromat is a lens (optics), lens that is designed to limit the effects of chromatic aberration, chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into ...
*Apochromatic lens
An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses.
The prefix ''apo-'' comes from the Greek preposition ''ἀπ ...
* The five Seidel aberrations
*Mangin mirror
In optics, a Mangin mirror is a negative meniscus lens with the reflective surface on the rear side of the glass forming a curved mirror that reflects light without spherical aberration if certain conditions are met. This reflector was invented i ...
References
Lenses 3 (number) {{optics-stub