optical fabrication and testing spans an enormous range of manufacturing procedures and optical test configurations. the manufacture of a conventional spherical lens typically begins with the generation of the optic's rough shape by grinding a glass blank. this can be done, for example, with ring tools. next, the lens surface is polished to its final form. typically this is done by lapping—rotating and rubbing the rough lens surface against a tool with the desired surface shape, with a .
a toric lens is a lens with different optical power and focal length in two orientations perpendicular to each other. one of the lens surfaces is shaped like a 'cap' from a torus see figure at right , and the other one is usually spherical. such a lens behaves like a combination of a spherical lens and a cylindrical lens.
the non-spherical curvature of an aspheric lens can also be created by blending from a spherical into an aspherical curvature by grinding the curvatures off-axis. dual rotating axis grinding can be used for high index glass that isn't easily spin molded, as the cr-39 resin lens is.
the geometry of the abrasive depends on the geometry of the workpiece surface; a stone rectangular shape is for cylindrical surfaces and cups and wheels are used for flat and spherical surfaces. a lubricant is used to minimize heat production, which can alter the metallurgical properties, and to carry away the swarf ; kerosene is a common lubricant.
viewing the mirror from behind the knife edge shows a pattern on the mirror surface. if the mirror surface is part of a perfect sphere, the mirror appears evenly lighted across the entire surface. if the mirror is spherical but with defects such as bumps or depressions, the defects appear greatly magnified in height.
a schmidt corrector plate is an aspheric lens which corrects the spherical aberration introduced by the spherical primary mirror of the schmidt or schmidt-cassegrain telescope designs. it was invented by bernhard schmidt in 1931, although it may have been independently invented by finnish astronomer yrjö väisälä in 1924 sometimes called the schmidt-väisälä camera as a result .
spherical aberration causes beams parallel to, but distant from, the lens axis to be focused in a slightly different place than beams close to the axis. this manifests itself as a blurring of the image. spherical aberration can be minimised with normal lens shapes by carefully choosing the surface curvatures for a particular application. for .
the newtonian telescope, . he later devised means for shaping and grinding the mirror and may have been the first to use a pitch lap to polish the optical surface. he chose a spherical shape for his mirror instead of a parabola to simplify construction; even though it would introduce spherical aberration, it would still correct chromatic aberration. he added to his reflector what is the .
that is, the curved shape would fit on the surface of a sphere. this is partly to do with the history of lens making but also because grinding and manufacturing of spherical surface lenses is relatively simple and cheap. however, spherical surfaces also give rise to lens aberrations and can lead to complicated lens designs of great size.
grinding produces higher dimensional accuracy of roundness and cylindricity. in addition, polished surface finishes of rz=0.3-0.8z cannot be achieved with hard turning alone. hard turning is appropriate for parts requiring a roundness accuracy of 0.5-12 micrometres, and/or surface roughness of rz 0.8–7.0 micrometres. it is used for gears .
the surface smoothness is measured in two ways: surface roughness and waviness. size refers to how tight are on the size, as measured by two parallel plates in contact with the ball surface. the starting size is the nominal ball diameter, which is the nominal, or theoretical, ball diameter.
spherical aberration causes beams parallel to, but distant from, the lens axis to be focused in a slightly different place than beams close to the axis. this manifests itself as a blurring of the image. spherical aberration can be minimised with normal lens shapes by carefully choosing the surface curvatures for a particular application.
lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. this can take two forms. the first type of lapping, involves rubbing a brittle material such as glass against a surface such as iron or glass itself with an abrasive such as aluminum oxide, jeweller's rouge, optician's rouge, emery, silicon carbide, diamond, etc., between them. this produces microscopic conchoidal fractures as the abrasive rolls about betwe
microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. for example, metal microparticles can be explosive in air. microspheres are spherical microparticles, and are used where consistent and predictable particle surface area is important.
a curved mirror is a mirror with a curved reflecting surface. the surface may be either convex or concave. most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. the most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. distorting mirrors are
surface finish of the part and the indenter do not have an effect on the hardness measurement, as long as the indentation is large compared to the surface roughness. this proves to be useful when measuring the hardness of practical surfaces. it also is helpful when leaving a shallow indentation, because a finely etched indenter leaves a much .
surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness. it comprises the small, local deviations of a surface from the perfectly flat ideal a true plane .