Confocal measuring microscope with automatic focusing

A confocal measuring microscope including a spectrometer and autofocus system sharing common optical elements in which the intensity of light entering the spectrometer from a particular spot on a workpiece is used to determine a focus condition for the same spot. The microscope includes at least one light source, an illumination field stop, and a microscope objective that images the stop onto a workpiece supported by a movable platform. The objective also forms an image of the illuminated portion of the object. An aperture in a second stop and intersecting the image plane passes light from part of the image to the spectrometer, while viewing optics are used to view the image. In one embodiment, a detector is placed at the zero order position, while in another embodiment a laser is placed at the zero order position. In the later embodiment an integrator circuit connected to the detector array replaces the zero order detector for measuring the total intensity of light entering the spectrometer. A best focus condition occurs when the total intensity is a maximum for a positive confocal configuration, i.e. where source and detector are on opposite sides of their respective field stops from said workpiece, and a minimum for a negative confocal configuration, i.e. where the source and workpiece are on the same side of a reflective illumination field stop with aperture. The movable platform may be scanned axially to achieve and maintain object focus as the object is scanned transversely.