When the first multi-lens microscopes were invented in 1590, scientists marveled at their new ability to see small objects and features in the natural world that were previously invisible to the eye and therefore seemingly nonexistent. With the constant miniaturization of parts and products in automated manufacturing over the past five decades, the use of microscopes has spread increasingly from science to industry. Today microscopes are found in a multitude of assembly and inspection applications wherever visualization and measurement of miniscule features are required.
The images now available to us are large, sharp and brilliantly illuminated. With such impressive imaging it’s easy to assume that the displays we see are dimensionally accurate, but this is not necessarily so. When studying a point whose distance from the lens is not precisely known or that is not located directly on the optical axis of a microscope’s lens system, fundamental principles of optics can introduce distortions that lead to observational and measurement errors. Standard optics can be sufficient for inspection of very two-dimensional objects such as the traces on a printed circuit board, or for qualitative analysis of non-flat objects. However, for precise measurement or comparison of features on a three-dimensional object, such as the curved surface of an injection molded part, such errors are problematic.