This week’s photos are brought to you by the letter “F” for “Fresnel”.
(Weekly Photo – Week #06, February 5, 2014)
About this time last year, I visited the Ponce de Leon Lighthouse, situated at the Ponce de Leon Inlet on the Atlantic coast of Florida. It is one of the few working lighthouses in the United States and this was the first time in my life that I had an opportunity to visit a lighthouse up close, so close that I climbed the stairs to the top. Although fascinated by the lighthouse, I was drawn to the lighting system used at the top of the lighthouse. (Lighthouse – light – lens – photography – see the connection?)
Most lighthouses, past and present, use a nifty piece of technology called the Fresnel lens, first used in 1823 and developed specifically for lighthouses by the French physicist Augustin‑Jean Fresnel. The lens design permits the construction of large aperture lenses with a short focal length, and without the mass and volume that would be required with a conventional lens design. This makes them ideal for capturing a light source, which can then be made visible over a great distance. The Fresnel lens is divided into one of six orders, based on the size and focal length.
In addition to the Fresnel lens in the Ponce de Leon Lighthouse, a museum on the property depicts the history of Fresnel lenses, some of which I have displayed through my photos in this blog posting.
Here is some background on the actual lighthouse and property for anyone visiting the area.
Work started on the Ponce de Leon Lighthouse in 1884 and on November 1, 1887, the lighthouse was activated for the first time with a first order fixed Fresnel lens illuminated by a kerosene lantern. In 1933, the service was electrified and a rotating third order Fresnel lens was installed. By 1970, the US Coast Guard abandoned the lighthouse, replacing it with a beacon on the south side of the Ponce Inlet. In 1972, the Town of Ponce Inlet acquired the deed to the lighthouse and surrounding property and the complete facility was restored as a museum. In late 1982, the Coast Guard installed a modern beacon in the tower and the lighthouse was officially reactivated as an aid to marine navigation.
The Ponce de Leon Inlet Light Station is now a National Historic Landmark and they have a web site at http://ponceinlet.org/ and you can take a virtual tour of the Fresnel lens museum at http://ponceinlet.org/virtual-tour-lens-exhibit.