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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.
These lenses are generally used for plus (hyperopic) corrections at about 12 diopters or higher. A similar sort of eyeglass lens is the myodisc, sometimes termed a minus lenticular lens, used for very high negative corrections. More aesthetic aspheric lens designs are sometimes fitted. [3]
The effects of extended contact lens wear on the cornea have been studied extensively and are well-documented. When determining the effects of long-term contact lens use on the cornea, many studies do not differentiate between users of hard and soft contact lenses, while studies that have made this differentiation have found similar results.
Wichterle thought pHEMA might be a suitable material for contact lenses and gained his first patent for soft contact lenses. In 1954 this material was first used as an orbital implant. In 1957 Wichterle produced around 100 soft lenses from closed polystyrene molds but the edges split and tore as the lenses were removed. In addition, they ...
The original Vitessa was introduced in 1950 with a fast Ultron 50 mm f /2.0 lens. [2] It was joined later by a version with a Color-Skopar 50 mm f /3.5 (Tessar-type) lens.. Contemporary marketing materials emphasized the rapid operation of the camera: by pressing the shutter release button, positioned on the top deck for the photographer's right index finger, the camera doors opened and the ...
The flashlight contains five lenses in the tailcap, consisting of two red lenses, a blue lens, a white lens, and a diffuser lens (earlier models utilized three red lenses and omitted the blue and green lenses). This feature enables soldiers to send color-coded signals or to preserve night vision. As the flashlight's focus is non-adjustable, the ...
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