Principles and features of dark-field microscopy
Dark-field microscope, also called dark-field microscope, is a special microscope to distinguish the details of samples by observing the scattered light produced when the samples are irradiated by lateral light.
1,The principle and structural characteristics of dark-field microscope
Dark-field microscope and general bright-field microscope is the difference between the two concentrator is different, dark-field microscope is equipped with a central darkening of the concentrator, so that the light can not pass through the concentrator, but only from the concentrator around the edges and not darkened parts of the oblique radiation to the specimen on the slide. Because the light is oblique, can not enter the objective lens, so the observation of the field of view is dark, and the concentrator oblique light to the bacterium, due to light scattering effect and make the bacterium emit bright light, reflected back to the objective lens, so that in the microscope can be seen in the dark field of view of the bright object image.
Dark field microscope is mainly used to check the morphology and motility of unstained specimens.
2,Methods of operation
①Use the research darkfield microscope, or remove the condenser on the ordinary optical microscope and replace it with the darkfield condenser.
② Whether using a dry objective or an oil-immersion objective, a large drop of cedar oil should be added to the upper lens of the concentrator during microscopy.
③ Place the prepared slice of the hanging drop specimen on the carrier table and raise the concentrator to the top to bring the oil into contact with the slide.
④ Magnify the light source .
⑤ Perform the concentrator optical axis adjustment and focusing. Use 10 * objective lens to find the object to be examined, close the concentrator iris aperture to the field of view can be seen in the field of view of the outline of the field of view diaphragm, and then slowly adjust the concentrator up and down, which will make the field of view diaphragm of the image of a clear, such as the field of view diaphragm is not in the centre of the field, the use of the two adjusting knobs to adjust the concentrator on the outside of the field of view when the bright spot adjusted to the centre of the field of view, and then open it up, you can carry out the observation.
3,Precautions
① dark field observation with the objective lens value of the aperture should be in 1.00-1.25 or so, too high, but the effect is not good, * it is better to use with the field of view diaphragm objective lens, turn the middle of the adjusting ring of the objective lens, you can change the value of the size of the aperture.
The slides and coverslips used must be free of scratches and dust, and the lens in front of the objective lens must be clean and dust-free. The thickness of slides and coverslips should be in accordance with the standard. The slide is too thick, the focus of the concentrator will fall in the slide, can not reach the plane of the object to be examined; the use of oil lenses, due to the working distance of the objective lens is very short, and even can not focus, so that you can not see or can not see the object to be examined.
③ The room should be dark during the microscopic examination; if there is no such condition, a light-shielding device should be used as far as possible to prevent the light around the eyepiece from coming in.
④ In the oil mirror mirror inspection, due to the diffuse reflection of the impurities and bubbles within the oil, it will hinder the field of view of the mirror effect, so it is required to get rid of the impurities and bubbles within the oil as much as possible.
