micrometria

Micrometria, or micrometry, is the field within metrology that deals with measuring the dimensions of objects visible only under a microscope. Measurements are typically expressed in micrometres, and in some cases nanometres, after appropriate calibration. The practice combines optical techniques, reference scales, and image analysis to obtain quantitative size information about microscopic features.

In light microscopy, micrometry relies on two key tools: an ocular micrometer, a scale etched into the eyepiece, and a stage micrometer, a slide with a precisely known scale. By imaging any slide with a known magnification, a conversion factor is established (micrometres per ocular division). In electron microscopy, calibration uses known standards or calibration grids to convert image dimensions, often expressed as a pixel size at a given magnification. Calibration is essential for accurate, comparable measurements and for traceability to recognized length standards.

Measurement procedures typically involve selecting the appropriate magnification, calibrating the scale, and then measuring features by counting divisions or using digital image analysis. For area or volume, planimetric methods or segmentation in images may be used, followed by computation from the calibrated dimensions. Image analysis can increase throughput and repeatability but depends on proper segmentation and correction for optical distortion.

Applications of micrometria span biology (cell size, pollen grains, organelles), histology, materials science (grain size, layer thickness, fiber dimensions), geology, and quality control. Limitations include optical distortion, refractive index effects, depth of field, sample preparation, and the need for rigorous calibration and uncertainty estimation to ensure measurement reliability.