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Hyper-radial or hyperradiant Fresnel lenses are Fresnel lenses used in lighthouses. They are larger than "first-order" lenses , having a focal length (radius) of 1330 mm (52.36 inches). The idea was mentioned by Thomas Stevenson in 1869 [ 1 ] and first proposed by John Richardson Wigham in 1872, and again proposed by Thomas Stevenson in 1885 ...
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.
The lens floated in a mercury bath to provide very low turning friction. These massive lenses are 81.46 inches (2,069 mm) high, with a focal length of 27.6 inches (700 mm). It weighed 3,530 pounds (1,600 kg). Relative to a sixth-order Fresnel, it was 11.54 times brighter, and would have a useful range of up to 20 nautical miles (37 km; 23 mi).
Close-up view of a flat Fresnel lens. This thin, lightweight, non-fragile and low-cost lens can be used as burning-glass in emergency situations. A makeshift burning glass, using the eyepiece of a telescope, being used to burn a leaf. Burning glasses (often called fire lenses) are still used to light fires in outdoor and primitive settings. [14]
The presence and continuous use of the original Third Order Fresnel lens makes this a relatively rare light. This is one of only seventy such lenses that are still operational in the United States, sixteen of which are use on the Great Lakes of which eight are in Michigan. [23] [24] It is listed on the National Register of Historic Places.
Augustin Fresnel invented a superior way of focusing light in the early 1850s and most lighthouses in the U.S. was converted to the Fresnel Lens, with Pemaquid Point receiving a fourth order Fresnel in 1856. The lens is one of only six Fresnel lenses still in service in Maine. [4] The keeper's house was built in 1857.
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