Measuring with microscope

Claim 1

An inspection or measurement microscope including means for producing and projecting a fiduciary image of fixed form onto the field of view of the microscope concurrently with means for projecting the image of an object to be measured and a calibrated mechanism adapted to translate the fiduciary image relative to the object image along a straight line to effect measurement of said object, said means for producing said fiduciary image adapted to produce said fiduciary image in the form of first and second pre-defined fixed boundaries each demarcating visually appreciable areas of relatively light and dark value, said boundaries being movable relative to the object image in the direction of said straight line and the sequence of light and dark areas at one of the boundaries being the reverse of the sequence at the other boundary, said calibrated mechanism enabling said fiduciary image to be relatively translated to determine between each said fiduciary boundary and a respective boundary of the image of said object a visually determinable null position when the boundary of said fiduciary image exactly coincides with the boundary of said object image as determined visually by the relative brightness of areas at said boundaries, said apparatus enabling measurement of the width of said object by determination of the position of said calibrated mechanism at said null positions thereby avoiding the need to split a beam into two object images and to move said images relatively.