Plasmat lens
Encyclopedia
The Plasmat lens is a widely used and long-established lens
type, especially common in large format
photography. It provides high correction of aberrations with a moderate maximum aperture
(e.g. ). It is a specific instance of the Dagor type Double-Meniscus anastigmat. Double-meniscus anastigmats use widely separated positive and negative surfaces, generally thick meniscus lenses, to achieve a flat field. The most basic form is two sharply curved meniscus elements located symmetrically about a stop. Further refinement of the form replaces the two simple meniscus lenses with achromats for chromatic correction. The Dagor type further refines these achromats into triplets with the following design parameters: a high-index, doubly convex (DCX) lens cemented to a medium-index, doubly concave (DCV) lens cemented to a low-index meniscus lens. Up to this point, all refinements have maintained symmetry about the stop. The Plasmat further refines the Dagor form by uncementing the meniscus allowing for placement away from the first two elements and removing the criteria of symmetry.
In its most basic form it is symmetrical and consists of two cemented groups of three lenses each. The innermost element in each group is a positive meniscus, the outermost is biconvex, and there is a biconcave element between them.
The Plasmat lens is made in many variants, e.g. departing from exact symmetry, adding a lens to one or both groups, or separating the innermost or outermost element from the rest of the group.
Standard lenses for large format cameras are generally of the Plasmat type, as are many macro lenses. Convertible lenses for large format photography often consist of Plasmat cells.
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
type, especially common in large format
Large format
Large format refers to any imaging format of 4×5 inches or larger. Large format is larger than "medium format", the 6×6 cm or 6×9 cm size of Hasselblad, Rollei, Kowa, Pentax etc cameras , and much larger than the 24×36 mm frame of 35 mm format.The main advantage...
photography. It provides high correction of aberrations with a moderate maximum aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
(e.g. ). It is a specific instance of the Dagor type Double-Meniscus anastigmat. Double-meniscus anastigmats use widely separated positive and negative surfaces, generally thick meniscus lenses, to achieve a flat field. The most basic form is two sharply curved meniscus elements located symmetrically about a stop. Further refinement of the form replaces the two simple meniscus lenses with achromats for chromatic correction. The Dagor type further refines these achromats into triplets with the following design parameters: a high-index, doubly convex (DCX) lens cemented to a medium-index, doubly concave (DCV) lens cemented to a low-index meniscus lens. Up to this point, all refinements have maintained symmetry about the stop. The Plasmat further refines the Dagor form by uncementing the meniscus allowing for placement away from the first two elements and removing the criteria of symmetry.
In its most basic form it is symmetrical and consists of two cemented groups of three lenses each. The innermost element in each group is a positive meniscus, the outermost is biconvex, and there is a biconcave element between them.
The Plasmat lens is made in many variants, e.g. departing from exact symmetry, adding a lens to one or both groups, or separating the innermost or outermost element from the rest of the group.
Standard lenses for large format cameras are generally of the Plasmat type, as are many macro lenses. Convertible lenses for large format photography often consist of Plasmat cells.