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How We See: The Light Microscope, Visual Routines, and the Microscopist


2022, Volume 69:4, pp. 147 – 159


Russ Crutcher and Heidie Crutcher

This paper addresses three critical aspects of analysis using the light microscope: 1) the human visual system, 2) the versatility of the light microscope, and 3) the importance of training and visual routines. The image of a particle produced by the light microscope is only an image, but it reveals important information about the shape, chemistry, and ontology of the particle. Changing the configuration of the microscope alters the image and provides additional information about the particle itself. While other analytical equipment generates graphs, tables, and charts, the microscope generates an image in the eye and brain of the microscopist. The microscopist is the detector for the microscope and the analyst of the signal generated by the detector. This is a two-part process. A fitting analogy is the concept of visual routines as used in the fields of computer vision and artificial intelligence. It refers to program modules that take raw images and process them into something intelligible. The term visual routines is being used here in this paper to address the relationship between the image generated by the retina, mental manipulation of the image, and by a specific configuration of the microscope. The microscopist needs to be trained to appreciate the analytical significance of different images of an object as the illumination system is changed. The addition of two polarizing filters to a transmitted brightfield image is one example. Understanding the light microscope as a sophisticated optical bench is part of the approach. Polarized light microscopy (PLM) and phase contrast microscopy (PCM) are limiting configurations but useful as two tools in the microscopist’s toolbox. There are many more transmitted light systems before even considering reflected light systems. An optimized light microscope is equipped with both a transmitted and reflected light system.

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