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  2. Lens (hydrology) - Wikipedia

    en.wikipedia.org/wiki/Lens_(hydrology)

    A freshwater lens on an island. In hydrology, a lens, also called freshwater lens or Ghyben-Herzberg lens, is a convex-shaped layer of fresh groundwater that floats above the denser saltwater and is usually found on small coral or limestone islands and atolls.

  3. Numerical aperture - Wikipedia

    en.wikipedia.org/wiki/Numerical_aperture

    In microscopy, NA is important because it indicates the resolving power of a lens. The size of the finest detail that can be resolved (the resolution) is proportional to ⁠ λ / 2NA ⁠, where λ is the wavelength of the light. A lens with a larger numerical aperture will be able to visualize finer details than a lens with a smaller numerical ...

  4. Ball lens - Wikipedia

    en.wikipedia.org/wiki/Ball_lens

    The first lenses were likely spherical or cylindrical glass containers filled with water, which people noticed had the ability to focus light. Simple convex lenses have surfaces that are small sections of a sphere. A ball lens is just a simple lens where the surfaces' radii of curvature are equal to the radius of the lens itself.

  5. Lens (geometry) - Wikipedia

    en.wikipedia.org/wiki/Lens_(geometry)

    A lens contained between two circular arcs of radius R, and centers at O 1 and O 2. In 2-dimensional geometry, a lens is a convex region bounded by two circular arcs joined to each other at their endpoints. In order for this shape to be convex, both arcs must bow outwards (convex-convex). This shape can be formed as the intersection of two ...

  6. Fermat's principle - Wikipedia

    en.wikipedia.org/wiki/Fermat's_principle

    According to the "strong" form of Fermat's principle, the problem of finding the path of a light ray from point A in a medium of faster propagation, to point B in a medium of slower propagation , is analogous to the problem faced by a lifeguard in deciding where to enter the water in order to reach a drowning swimmer as soon as possible, given ...

  7. Ibn Sahl (mathematician) - Wikipedia

    en.wikipedia.org/wiki/Ibn_Sahl_(mathematician)

    The lower part of the figure shows a representation of a plano-convex lens (at the right) and its principal axis (the intersecting horizontal line). The curvature of the convex part of the lens brings all rays parallel to the horizontal axis (and approaching the lens from the right) to a focal point on the axis at the left.

  8. Total internal reflection - Wikipedia

    en.wikipedia.org/wiki/Total_internal_reflection

    Fig. 1: Underwater plants in a fish tank, and their inverted images (top) formed by total internal reflection in the water–air surface. In physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into ...

  9. Geometrical optics - Wikipedia

    en.wikipedia.org/wiki/Geometrical_optics

    Thin lenses produce focal points on either side that can be modeled using the lensmaker's equation. [5] In general, two types of lenses exist: convex lenses, which cause parallel light rays to converge, and concave lenses, which cause parallel light rays to diverge. The detailed prediction of how images are produced by these lenses can be made ...