Cylindrical lenses have at least one surface that is formed like a portion of a cylinder. Cylindrical lenses are used to correct astigmatism in the eye, and, in rangefinders, to produce astigmatism, stretching a point of light into a line. Some styles of cylindrical lenses have antireflective coatings to increase the transmission of light through the lens.
Cylindrical lenses are available in either plano-concave or plano-convex configurations. Plano-concave lenses have a negative focal length and are used for image reduction or to spread light. Plano-convex lenses have a positive focal length, which makes them ideal for collecting and focusing light for many imaging applications.
Cylindrical lenses have at least one surface that is formed like a portion of a cylinder. Cylindrical lenses are used to correct astigmatism in the eye, and, in rangefinders, to produce astigmatism, stretching a point of light into a line. Some styles of cylindrical lenses have antireflective coatings to increase the transmission of light through the lens.
Cylindrical lenses are available in either plano-concave or plano-convex configurations. Plano-concave lenses have a negative focal length and are used for image reduction or to spread light. Plano-convex lenses have a positive focal length, which makes them ideal for collecting and focusing light for many imaging applications.
Three main material types are used in the design of cylindrical lenses. These include glass materials, plastics and a wide “other” grouping. Glass is a popular material because it tends to reflect in the infrared range. Within this grouping, crown glass and flint glass are the principle types. Crown glass is harder than flint glass, and has a lower index of refraction and lower dispersion. Both types are used in the production of compound lenses. Crown glass has an Abbe v-value larger than 50 or 55, depending on its index. It generally has an index of refraction of 1.495-1.54. Flint glass is softer than crown glass, has a higher dispersion and usually a higher refractive index. Flint glass has an Abbe v-value of 35-40. It generally has an index of refraction of 1.595-1.64.
Plastic cylindrical lenses tend to absorb light in the ultraviolet range. Some of the more common types of plastics used include acrylics, amorphous polyolefin, polycarbonate, and polystyrene.
Other materials used for cylindrical lenses are preferred for their applications in a particular area of the spectrum or for a wide transmission bandpass. Some of these “other” materials include calcium fluoride (transmission from 150nm through 7000nm), germanium (transmission in the infrared from 2000nm to 4000nm), sapphire (transmission range extending from 150 nm to 6000nm), zinc selenide (transmission from .69m to 18m), and UV grade fused silica (improved transmission in the ultraviolet region compared with crown glass).
