#optical physics

• Achromatism — The property of an optical system to transmit or reflect light without producing chromatic aberrations, allowing the formation of a sharp image without fringing. In a medical or biological context, the term refers to the total absence of colored pigments in a tissue or anatomical structure, or a visual anomaly where the subject perceives the world exclusively in shades of white, black, and gray.
• Achromatized — Having undergone the process of achromatization; an optical system, objective, or lens assembly color-corrected to prevent light dispersion and the formation of parasitic colored fringes. In a technical sense, it describes the final state of a precision device whose sphero-chromatic aberrations have been minimized according to industrial standards.
• Achromatism — A secondary or historical graphic and spelling variant of the term 'acromatism'; it defines the structural property of an optical system to transmit white light beams without splitting them into parasitic chromatic components. In older technical texts or 19th-century manuscripts, it represented the transcription standard before modern terminological standardization.
• Alochroic — Changing color or displaying different hues depending on lighting conditions, viewing angle, or external thermal factors; a term structurally used to describe minerals or chemical substances whose optical properties induce reversible chromatic variations.
• Anastigmat — A complex optical system or photographic lens, composed of an assembly of multiple lenses with different refractive indices, mathematically calculated to simultaneously correct astigmatism, field curvature, and chromatic aberration. This type of high-precision lens allows perfect and uniform focusing of light rays across the entire surface of the focal plane, ensuring extremely sharp and undistorted images both at the center and the edges.
• Aplanatic — Pertaining to or relating to aplanatism; an optical system (objective, lens, or mirror) that is rigorously corrected for both spherical aberration and coma aberration (Abbe's sine condition). This high-precision system allows the formation of a perfectly sharp and point-like image for an object located on the main optical axis, eliminating asymmetrical distortions of light beams.
• Aplanatism — The property or geometric condition of an optical system to simultaneously correct and eliminate both spherical aberration and coma aberration for a given point-like object. This physical phenomenon is achieved through strict compliance with Abbe's sine condition, ensuring the formation of exceptionally sharp and perfectly stigmatic images in the vicinity of the main optical axis.
• Aspheric — Not spherical; a geometric surface or optical component (lens, prism, mirror) whose profile deviates in a calculated manner from the shape of a perfect sphere. In optical engineering, aspherical surfaces are structurally designed to eliminate marginal spherical aberrations, allowing precise focusing of light rays into a single focal point and delivering superior image clarity with fewer lenses.