The Fresnel Lens Posted August 31, 2018 One of the plano-convex lenses that make up Old Mackinac Point’s original lens. These simple lenses, sometimes called bullseyes, could be grouped together to project multiple beams of light. Fresnel lenses served as the heart of lighthouses around the world, including at Old Mackinac Point. Invented by French scientist Augustin-Jean Fresnel in 1819, these brass and glass beehives bent, magnified, and focused light to project brilliant beams for miles. (more…)
Coming Soon to Old Mackinac Point Posted February 9, 2018 Although the museums and historic sites are closed, winter is a busy time here at Mackinac State Historic Parks! One of many projects currently taking place is the installation of a new science and technology exhibit at the Old Mackinac Point Lighthouse in Mackinaw City. (more…)
What’s Missing at Old Mackinac Point? Posted June 2, 2017 When you visit the Old Mackinac Point Light Station today, you are stepping back in time to the early years of the 20th century. Since 2004, Mackinac State Historic Parks has been working to return the station grounds to their appearance just over 100 years ago. Three original buildings- the 1892 keepers’ quarters and tower, the 1906 fog signal building, and the 1892 barn- have all been restored to their original appearance, while the 1890 warehouse was reconstructed to match the original in 2014. The station looks complete, but there are still a few elements missing. (more…)
Lamps and Lenses: How Old Mackinac Point Shed its Light Posted December 17, 2012 What puts the light in a lighthouse? Until 1913, a single lamp provided the light for the beacon at the Old Mackinac Point Lighthouse. This lamp is similar to the one used in the first 20 years of the lighthouse’s existence. It was eventually replaced with a gas lamp and then an electric light. This diagram shows how even a small amount of light from the lamp could be magnified using a number of prisms in a Fresnel lens. (Click to enlarge) Like most other lighthouses in the United States, Old Mackinac Point used a kerosene lantern not unlike those still found in many homes today. Keeper George Marshall’s duties included regularly fueling the lamp, as it burned over 5 ounces of kerosene per hour. A red glass lamp chimney originally produced a red light, helping sailors identify Old Mackinac Point. Both the kerosene lamp and red light were replaced in 1913, when the U.S. Lighthouse Service installed an incandescent oil vapor mechanism, which produces a white light similar to a modern camping lantern. While the kerosene lamp itself shone brightly, a fourth-order Fresnel lens amplified the Old Mackinac Point light until it was visible to a distance of 16 miles. The lens contained a series of stacked magnifying glasses around its center, with each glass focusing the light from the one beneath it. Prisms ringed the lens above and below the magnifying glasses. These prisms caught and bent more light, focusing it into the central beam created by the magnifiers. The entire lens rotated around the lamp, creating a flashing signature (one flash every 10 seconds) unique to Old Mackinac Point.
