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Confocal optical microscopy offers major improvements and usefull investigative capabilities, over conventional microscopical
imaging, expecially when high contrast and focal plane discrimination are required. Confocal operation implies space selective
illumination and light detection. Potential uses can be both in the field of transmitted-light analysis of absorbing specimens or with
incident-light configurations. Provisions for spatial scanning have to be included in the instrument and a variety of electromechanical
solutions have been suggested by others, adaptable to incident-light work. Point illumination and detection is typical of
proposed instruments and of their commercialy available versions, being principally suited to reflectance and fluorescence
investigations. In current designs , intermediate deflection devices provide two dimensional scanning of the object, using a spot of
concentrated light. The illuminated position of the object, is imaged back by the same optics on the spatial filter ( pin hole) placed
in front of a photo-detecting device. Instruments of this type are of limited utility, in transmitted light work, since the scanning
configuration doesn't permit to perform transmitted light confocal imaging. In fact an intrinsic limitation is due to the difficulty of
designing and constructing a scanning device that guarants precise and stable correspondence between the position illuminated and the
position detected which, in the case of transmission analysis reside on the opposite halves in the optical path, with respect to the
specimen.
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