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The Abbe diagram is created to compare various glass types based on Abbe number and refractive index for a certain wavelength. A high Abbe number indicates low chromatic aberration, and a low Abbe number indicates high chromatic aberration. The Abbe number is inversely related to the amount of chromatic aberration. Also known as the V-number, the Abbe number combines the refractive indices of a material at three wavelengths (486.1 nm blue from hydrogen, 589.2 nm yellow from sodium, and 656.3 nm red from hydrogen) to approximate the amount of chromatic aberration a material will have when visible light passes through it (Figure 3). In the late 1800s, German physicist Ernst Abbe, a colleague of Carl Zeiss, created the Abbe number, a measure of the magnitude of chromatic dispersion for the visible spectrum. Calculation of the Abbe number to describe the amount of chromatic dispersion for a medium. This can be visualized on images at bright to dark boundaries as “fringes” of color. Each wavelength of light will thus be focused at a different distance away from the lens. In Figure 2, a single lens demonstrates chromatic aberration as different wavelengths of light have different focal lengths after passing through the lens. As a result, the index of refraction for a given medium will vary based on the wavelength of light going through it. When a single beam composed of multiple wavelengths of light passes through a lens, each wavelength of light will change direction and speed to different extents. The interaction of the particular wavelength of light with electrons in the medium gives rise to this phenomenon. Chromatic DispersionĬhromatic dispersion, also referred to as chromatic aberration, is a phenomenon where the speed and direction of light propagation in an optical medium depends on the wavelength of light. Chromatic aberration results in a single beam of light to have a different focal point for each wavelength. Lens Material Properties Index of Refractionįigure 2. Critical lens properties include refractive index, Abbe number (chromatic dispersion), specific gravity, and ultraviolet absorption. Lenses can be produced using a variety of materials and designed with several optical profiles to optimize use in specific applications. Eyeglasses also serve an important role in protecting the eyes from physical trauma and harmful radiation. Both lenses and prisms are also frequently used to improve eye alignment and treat diplopia in strabismus.
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Corrective spherocylindrical lenses are commonly used to treat refractive errors such as myopia, hyperopia, presbyopia, and astigmatism.