一. The difference between light and dark field of microscope
The bright field of metallographic microscope is illuminated by coaxial light of microscope, and the light shines on the surface of the object, and then reflects back to the objective lens, which is observed by our naked eyes through the eyepiece. Under the eyepiece, the reflective part of the sample is bright, while other places that are scattered or unable to reflect light are black or dark.
The main differences are as follows:
1). Bright field is to let the light beam directly enter the objective lens after passing through the specimen, and the field of view is bright.
2). The dark field is a strong and narrow beam that irradiates the specimen without letting the beam directly enter the objective lens, but the particles in the specimen can scatter light, and some of these scattered light enters the objective lens, so the particles in the specimen can also be seen shining on the dark background.
二. The working principle of dark field microscope
Dark field microscope technology is to use oblique illumination to block the direct light passing through the details of the specimen, and to observe the specimen with reflected light and diffracted light. When the direct light passes through the specimen under the ordinary microscope, part of the light is absorbed, and the other part is transmitted or refracted, forming a true projection of the internal structure of the specimen details. Therefore, what is seen under the ordinary microscope is the shape and structure of the object. However, under the dark field microscope, the light beam irradiated from the side to the object diffracts or reflects, resulting in the silhouette of the object. Therefore, what is seen under the dark field microscope is only the outline of the object or the movement of the object.
The details of 0.45um can be seen under the ordinary microscope, but the tiny objects of 0.2-0.004um can be seen under the dark field microscope. The objects in this range are called sub-particles, so the dark field microscope can also be called the finch's microscope outside the crack limit.
Dark-field microscope is especially suitable for observing Brownian motion of solute particles in colloidal chemistry, flagella and pseudopodia motion of protozoa and bacteria, and medical laboratory science is suitable for observing spirochetes, urine tubes, crystals or various particles in human body fluids. In this regard, dark-field microscope is far superior to other kinds of microscopes.
三. The application of dark field microscope
Dark field microscope is mainly used to observe the edge, contour, boundary and refractive index gradient of objects, especially suitable for displaying tiny aquatic organisms, diatoms, small insects, bones, fibers, hair, undyed bacteria, yeast, tissue culture cells and protozoa.
Dark field microscope, also known as dark field microscope, is a special microscopic observation technology. Through special optical configuration, light or electrons outside the observed object enter the objective lens, so that the background of the field of view observed in the eyepiece is black and only the edge of the object is bright. This technique can observe particles as small as 4~200nm, and its resolution is 50 times higher than that of ordinary microscopy. Dark field illumination is especially suitable for displaying contours, edges, boundaries and refractive index gradients, so it is an ideal choice for displaying tiny objects.
Dark field microscope has a wide range of applications, including but not limited to:
Shows the details of minerals and chemical crystals.
Observe colloidal particles and dust count samples.
Show polymer and ceramic flakes containing fine inclusions, porosity differences or refractive index gradients.
In addition, the dark field microscope also has its unique role in material analysis, especially when it is necessary to observe small objects with high resolution. The dark field microscope provides higher definition and contrast than the traditional bright field observation, making the observed objects more clearly visible. This technology is not only suitable for scientific research, but also widely used in industrial detection, medical diagnosis and other fields.
