eclectic echoes
Red Light Fresnel
A shot through the red fresnel lens on the Ledge Lighthouse's light.
I love optics - reflection, refraction, diffraction and polarization are all properties of light and light transmission that Augustin Fresnel studied and described mathematically. The fresnel lens he invented in 1822 has saved countless lives and is still used today. Previous lighthouse technology used mirrors to focus and "throw" light at most a few miles. With the fresnel lens a decent light can be seen up to 20 miles or more away and more importantly, it can be seen in heavy fog, where a mirror thrown light often can't.
The fresnel lens essentially works by becoming a giant magnifying glass. But to construct a magnifying glass large enough to fit a lighthouse lamp window would be prohibitively thick and expensive, requiring pretty tight manufacturin tolerances. Fresnel discovered that the important aspect of the magnifying lens is the curvature of the lens surfaces. The fresnel lens essentially duplicates the magnifying glass's curved front surface, but in small sectiona and it removes the "excess" material behind it. The resulting lens of concentric rings has the same focal length and magnification power of a traditional magnifying glass of the same size, but with a fraction of the wieght.
Fresnel lenses are not without problems, primarily the intersections between rings causes focus issues that makes them unusable for most imaging applications. The grooves at each ring junction also creates severe chromatic abberation, again making fresnel lenses unsuited to most imaging purposes. However, if you work in multispectral or hyperspectral imaging you can take advantage of these abberations and by tuning the grooves, predictably split out the spectra along an axis with sensors to pick them up. Tunable, high magnification hyper-spectral sensor array. From an 1822 design made by and named for one of optics early geniuses.
I LOVE SCIENCE!!
Red Light Fresnel
A shot through the red fresnel lens on the Ledge Lighthouse's light.
I love optics - reflection, refraction, diffraction and polarization are all properties of light and light transmission that Augustin Fresnel studied and described mathematically. The fresnel lens he invented in 1822 has saved countless lives and is still used today. Previous lighthouse technology used mirrors to focus and "throw" light at most a few miles. With the fresnel lens a decent light can be seen up to 20 miles or more away and more importantly, it can be seen in heavy fog, where a mirror thrown light often can't.
The fresnel lens essentially works by becoming a giant magnifying glass. But to construct a magnifying glass large enough to fit a lighthouse lamp window would be prohibitively thick and expensive, requiring pretty tight manufacturin tolerances. Fresnel discovered that the important aspect of the magnifying lens is the curvature of the lens surfaces. The fresnel lens essentially duplicates the magnifying glass's curved front surface, but in small sectiona and it removes the "excess" material behind it. The resulting lens of concentric rings has the same focal length and magnification power of a traditional magnifying glass of the same size, but with a fraction of the wieght.
Fresnel lenses are not without problems, primarily the intersections between rings causes focus issues that makes them unusable for most imaging applications. The grooves at each ring junction also creates severe chromatic abberation, again making fresnel lenses unsuited to most imaging purposes. However, if you work in multispectral or hyperspectral imaging you can take advantage of these abberations and by tuning the grooves, predictably split out the spectra along an axis with sensors to pick them up. Tunable, high magnification hyper-spectral sensor array. From an 1822 design made by and named for one of optics early geniuses.
I LOVE SCIENCE!!