Top Ten in Up Close To A Lighthouse Lamp Challenge, 14-Jul-2013
This beautiful lens is at the Beavertail Light museum on Conanicut Island in Rhode Island.
Beavertail Lighthouse, built in 1749, was and still is the premier lighthouse in Rhode Island, USA, especially for entrance into Narragansett Bay. The 45-foot (14 m) lighthouse lies on the southernmost point of Conanicut Island in the town of Jamestown, Rhode Island in Beavertail State Park.
In 1989, following a joint effort by the US Coast Guard, Rhode Island Parks Management, the Rhode Island Department of Environmental Management, and the town of Jamestown, the building was restored and reopened to the public. In 1993, Beavertail Lighthouse Museum Association (BLMA) was established to oversee the operations of the Beavertail Lighthouse Museum, which is located in the assistant keeper’s house. The museum includes a Fresnel lens (which I photographed and have displayed here), and the history of, models and photos of many Rhode Island lighthouses.
A Fresnel lens is a type of compact lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.
The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances.
According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary; its light could be seen from more than 20 miles (32 km) out. Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses.
for full info you can go to the Wikipedia page on Fresnel lens:
The Fresnel lens displayed here is a third order lens, focal length of 500mm, 1.576m height.