Friday, April 12, 2013

Fresnel Lens

Ocracoke Lighthouse was built in 1823. One year before that, French physicist Augustin-Jean Fresnel invented the compact lighthouse lens that bears his name. The Fresnel Lens is actually a remarkable series of prisms that capture and focus light, allowing a lighthouse beam to be visible many miles off shore.

Originally the Ocracoke Lighthouse was equipped with a simple reflecting illuminating apparatus. By 1854 the superiority of the Fresnel Lens was acknowledged, and such a new lens was installed.

Ocracoke's 4th Order Fresnel Lens


















Ocracoke's light is magnified by a fourth order Fresnel Lens with a focal length of 250 mm. Although the lighthouse was originally built to guide mariners through Ocracoke Inlet and into deeper waters of Pamlico Sound, its steady beam can be seen 14 miles to sea.

Our latest Ocracoke Newsletter is a video of Philip Howard telling the story of the 1861 wreck of the Black Squall. You can watch it here: http://www.villagecraftsmen.com/news032113.htm.

13 comments:

  1. And the Fresnel lens is used on aricraft carriers as a visual landing aid, replacing the mirror system orignally invented by the British Navy. If a pilot adjusts his rate of descent to keep the "meatball" reflection right between the green datun lights on either side, the airplane is exactly on a glide path which will result in catching a wire. Thanks Augustin-Jean; especially at night!

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  2. Anonymous11:29 AM

    Did the Fresnel lens upgrade still keep the lighthouse "under budget"

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    1. US lighthouses then were managed and maintained by the Treasury Department. Like any structure (private or public), lighthouses and keeper's quarters needed periodic maintenance and repair. The first major Ocracoke lighthouse expense that I am aware of was the installation of the Fresnel lens in 1854. That was 31 years after construction. In March of the next year "the keepers dwelling and tower at this station were thoroughly repaired." I do not know what the 1854/1855 Treasury Department budget was.

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  3. Wesley12:04 PM

    Fresnel lenses are beautiful things. I was able to make arrangements and visit the Aids to Navigation Museum at the Coast Guard Training Center in Yorktown, VA some years back. They have a beautiful collection of Fresnel lenses. I have photos posted online at http://www.megley.com/photos/trips/naton/ if anyone wants to take a look...

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    Replies
    1. Thanks for sharing. They truly are beautiful.

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  4. Anonymous1:52 PM

    Thanks from me as well-this is quite a collection. They are functional art that's for sure. Would love to have one in one of the yard gardens but what would the neighbors say?! SueM

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    Replies
    1. Wesley12:49 PM

      Careful...if the sun hits it just right, it's liable to start a fire! :-)

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  5. Anonymous5:06 PM

    From Kevin Duffus:

    Fresnel's original lens was a circular band of polygonal bulls-eye flash panels with rows of angled mirrors above and below mounted on an iron drum-like frame that rotated around a single light source. Essentially, the flashing light produced by a single oil lamp was the radical improvement of Fresnel's design

    Over the two decades following Fresnel’s untimely death, many other lens makers and lighthouse engineers improved his design, including the famous Stevenson family of Scotland who introduced crown glass prisms to replace Fresnel's mirrors. It should truly be named the "Fresnel-Stevenson" lens. The classical Fresnel lens was truly a miracle of Victorian-era ingenuity, producing a brilliant projection of light using more than 80% of the light source and producing significantly less heat and using less fuel.

    Kevin Duffus, author of "The Lost Light-A Civil War Mystery"

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  6. Anonymous5:48 PM

    Will the shops and restaurants still be open the last week of October?

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    Replies
    1. Many of the shops and restaurants are normally open the last week of October. I am guessing that will be true this year.

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  7. Anonymous5:06 PM

    Thanks for the information!

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  8. Anonymous1:21 PM

    Careful...if the sun hits it just right, it's liable to start a fire! :-)

    ReplyDelete
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