Definition
A microscope is a precision observation instrument that uses optical or electronic principles to magnify tiny objects to the level that the human eye can discriminate. It realizes visual observation and recording of the microstructure of the sample through the combination of objective lens and eyepiece, or the interaction of electron beam with electromagnetic lens. As one of the basic tools in laboratories, microscopes play a key role in scientific research, industrial testing, and medical diagnosis.
Principle
Optical microscopes work based on the principles of geometric optics and physical optics. The light shines through the condenser to illuminate the sample, and the transmitted or reflected light forms a magnified real image through the objective lens, which is further magnified into a virtual image through the eyepiece for observation. Its magnification is the product of the objective lens and the eyepiece magnification, and the resolution is limited by the Abbe diffraction limit, and the formula is:d = λ/(2NA)where d represents the minimum resolution distance, λ is the wavelength of the light source, and NA is the numerical aperture of the objective lens. Electron microscopy uses electron beams instead of light sources, uses electromagnetic lenses to focus, and scatters electrons through samples for imaging, with resolutions up to the sub-nanometer level.
Measurement method
Microscopic measurements are usually calibrated in combination with eyepiece micrometers and objective micrometers. First, calibrate the eyepiece reticle plate using an objective micrometer with a known scale to determine the actual length corresponding to the unit scale. When measuring, the sample is placed on the stage, and the focus is adjusted to obtain a clear image, and the calibrated reticle plate is used to read the dimensions directly. For three-dimensional topography measurement, confocal scanning technology can be used to reconstruct layer by layer. Compositional analysis needs to be combined with accessories such as energy spectrometers to achieve elemental identification.
Influencing factors
The observation effect is affected by multiple factors. In terms of optical systems, the numerical aperture of the objective lens determines the light collection ability and resolution, and the illumination method (Kohler illumination or critical illumination) affects the imaging uniformity. During sample preparation, the slice thickness, staining contrast, and refractive index of the mounting medium will all change the imaging quality. Environmental factors such as mechanical vibration and temperature fluctuations can cause image drift. The operator's technical proficiency, including focusing accuracy and interpupillary distance adjustment, also directly affects observation efficiency.
Application
In the life sciences, microscopes are used for cell morphology observation, histopathological analysis, and microbial identification. In materials science, metal crystal phases, polymer cross-sections and composite interfaces can be studied. In terms of industrial inspection, it is used in semiconductor defect investigation, precision part dimensional measurement and surface roughness assessment. Geology analyzes mineral components with the help of polarizing microscopes, and forensic appraisal uses comparative microscopy to compare traces. With the development of digital imaging technology, microscopy systems can also enable dynamic process recording and quantitative image analysis.
Selection
The selection of the type should comprehensively consider the observation requirements and system configuration. The type of microscope is selected according to the characteristics of the sample: transmissive is suitable for transparent thin layer samples, and reflective is suitable for opaque materials such as metals. The magnification range should cover basic observation and detailed analysis, and the conventional configuration is 40x to 1000x. Consider configuring modular accessories such as fluorescence modules, phase contrast rings, or differential interference components to accommodate specific observation patterns. In terms of ergonomics, attention is paid to the number of eyepieces, the feel of the focusing mechanism and the comfort of long-term operation. System scalability includes support for digital imaging, image analysis software compatibility, and automation platform interfaces. Maintenance costs involve factors such as light source life, objective cleaning requirements, and calibration intervals.