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A spherometer is an instrument used for the precise measurement of the radius of curvature of a curved surface. Originally, these instruments were primarily used by opticians to measure the curvature of the surface of a lens .
Lens clock. A lens clock is a mechanical dial indicator that is used to measure the dioptric power of a lens.It is a specialized version of a spherometer.A lens clock measures the curvature of a surface, but gives the result as an optical power in diopters, assuming the lens is made of a material with a particular refractive index.
It is used extensively in architecture when calculating the arc necessary to span a certain height and distance and also in optics where it is used to find the depth of a spherical mirror or lens. The name comes directly from Latin sagitta , meaning an " arrow ".
Deep blue ray refers the radius of curvature and the red line segment is the sagitta of the curve (black).. In optics and especially telescope making, sagitta or sag is a measure of the glass removed to yield an optical curve.
A spherical lens or mirror surface has a center of curvature located either along or decentered from the system local optical axis. The vertex of the lens surface is located on the local optical axis. The distance from the vertex to the center of curvature is the radius of curvature of the surface.
In lens systems, aberrations can be minimized using combinations of convex and concave lenses, or by using aspheric lenses or aplanatic lenses. Lens systems with aberration correction are usually designed by numerical ray tracing. For simple designs, one can sometimes analytically calculate parameters that minimize spherical aberration.
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An aspheric biconvex lens. An aspheric lens or asphere (often labeled ASPH on eye pieces) is a lens whose surface profiles are not portions of a sphere or cylinder.In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.