Modern CCD cameras that are typically produced in high volume for consumer and machine vision applications can be used as precisely calibrated image sensors. New CCD chips with on-chip micro lens arrays, however, have some characteristics that limit design choices where precise illumination uniformity is required. The micro lenses cause vignetting and limit the angular aperture of each pixel. This paper measures vignetting and consequent shading for a typical micro lensed CCD chip. Nevertheless, when properly designed, camera system employed these advanced CCd chips can be precisely calibrated with respect to face plate irradiance.
Most imaging optical systems require a fixed and stable relationship between the object and the image. Tilting and decentering of optical components due to manufacturing tolerances or thermal expansion will cause the image to move or tilt about the desired position. A method of modeling imaging optical systems is presented which uses affine transformations based on the paraxial optical equations. The method uses matrix and vector equations which are easily input, usually exactly as they are written, into many of today's math software programs for personal computers. Structural influence coefficients, or sensitivities, are derived for several common optical components. The resulting sensitivities can be computed and used in optomechanical tolerance budgeting. The equations can also be used as stabilization equations in actively controlled optical systems.
In any optical imaging system, tilting and decentering of optical components will cause the relationship between the object and image to change. Many precision imaging systems require the image to have a fixed relationship to the object within a certain tolerance. To obtain an object-to-image relationship within a specified tolerance, each of the possibly many components must in turn be positioned within certain tolerances. The allowable tilt and decenter of each component depends upon the sensitivity of the image position to that component's motion. This sensitivity is often referred to as a structural influence coefficient. A method is presented for the derivation and calculation of structural influence coefficients for finite conjugate optical imaging systems. A special differential rotation operator is introduced to model tilts of optical components. The method most easily results in numerical coefficients with the use of a personal computer and almost any common mathematical software package.
The basis of confocal microprobes, in general, is that light or other radiation is focused to a point where it is scattered by some material under study and then collected by a lens and detector system which is also focused on that point. The amount of radiation collected at the detector is then indicative of the scattering properties of the material at the common focus. This paper describes a family of related microprobes using optical fibers for delivering light to and from the focus. A novel arrangement is described wherein the focal points of the source and detector are not confocal but adjacent. This quasi-confocal arrangement has some very useful properties for detecting surfaces and investigating surface topography.
When machine vision utilizing pattern recognition for precise position measurement is used, special emphasis on spatial filtering, stability, and repeatability of the optical image is required. The opposing requirements of a large field of view, which provides for rapid searching, and a high magnification, which provides for higher accuracy, can be mutually exclusive when the image detector is a small CCD array with a finite pixel size. A video microscope for machine vision is described whose key design requirements were appropriate resolution, low cost, a given small space of predetermined shape, two fixed and precise magnifications to be achieved with given object-to-image distances, illumination evenness of 5% or better, and having both dark and bright field illumination.
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