Common methods of observation used with optical microscopes
A light microscope is an optical instrument that uses light as a source to magnify and observe tiny structures that are invisible to the naked eye. *The earliest microscope was made by an optician in 1604.
Over the past two decades, scientists have discovered that optical microscopes can be used to detect, track, and image objects that are smaller than half the wavelength of conventional visible light, or a few hundred nanometers.
Because optical microscopes have not traditionally been used to study the nanometer scale, they often lack calibrated comparisons to standards to check that the results are correct for accurate information at that scale. A microscope can** consistently indicate the same position of an individual molecule or nanoparticle. However, at the same time, it can be highly inaccurate, and the position of an object identified by a microscope to within a billionth of a meter may in fact be a millionth of a meter, because there is no error.
Optical microscopes are common in laboratory instruments and can easily magnify different samples, from delicate biological samples to electrical and mechanical devices. Similarly, optical microscopes are becoming increasingly capable and affordable as they combine the lights in your smartphone with a scientific version of a video camera.
Common Observation Methods for Optical Microscopes
Differential Interference (DIC) observation method
Principle
Polarized light is broken up into mutually perpendicular, equal-intensity beams by means of a special prism. The beams pass through the examined object at two extremely close points (smaller than the resolution of the microscope), thus differing slightly in phase, giving the image a stereoscopic three-dimensional feel.
Features
Can make the examined object produce three-dimensional three-dimensional feeling observation effect is more intuitive. No special objective lens is required, and it works better with fluorescence observation, and the color change of the background and the object can be adjusted to achieve the desired effect.
Darkfield Observation Method
Dark field is actually dark field illumination. It is different from bright field in that it does not directly observe the illuminated light, but the light reflected or diffracted from the object being examined. As a result, the field of view is a dark background, while the examined object presents a bright image.
The principle of dark field of view is based on the Tyndall phenomenon in optics, where fine dust cannot be observed by the human eye in the case of a strong direct light passing through it, which is caused by the strong light being directed around it. If light is directed at it obliquely, the particles seem to increase in size due to the reflection of light and become visible to the human eye. A special accessory required for dark-field observation is a dark-field spotting scope. It is characterized by not letting the light beam pass through the examined object from bottom to top, but changing the path of the light so that it is directed obliquely towards the examined object, so that the illuminating light does not enter directly into the objective lens, and a bright image is formed by using the reflected or diffracted light from the surface of the examined object. The resolution of dark-field observation is much higher than bright-field observation, reaching 0.02-0.004μm.
