Dark field microscopy
Dark field microscopy
A dark field microscope, also known as a dark field microscope, is a special microscope that distinguishes the details of a sample by observing the scattered light generated when the sample is illuminated by lateral light.
1. The principle and structural characteristics of a dark field microscope
The difference between a dark field microscope and a general bright field microscope lies in the difference in their condenser. A dark field microscope is equipped with a central darkened condenser, which prevents light from passing through the condenser and can only slant from the periphery of the condenser and the unshaded area to the specimen on the slide. Due to the fact that light is angled and cannot enter the objective lens, the field of view for observation is dark. However, the light that is angled by the condenser onto the mycelium emits bright light due to light scattering, which is reflected into the objective lens. This way, bright objects in the dark field can be seen in the microscope.
The dark field microscope is mainly used to examine the morphology and motor ability of unstained specimens.
2. Operation method
① Use a research dark field microscope or remove the condenser from a regular optical microscope and replace it with a dark field condenser.
② Whether using a dry objective or an oil immersed objective, a large drop of tar should be added to the upper lens of the condenser during microscopic examination.
③ Place the prepared suspension sample slide on the stage and raise the condenser to the top to allow the oil to come into contact with the slide.
④ Zoom in on the light source.
⑤ Adjust and focus the optical axis of the condenser. Use a 10 objective lens to locate the object being examined, turn down the iris aperture of the condenser until the outline of the field of view diaphragm can be seen in the field of view, and then slowly adjust the condenser up and down to make the image of the field of view diaphragm clearer. If the field of view diaphragm is not in the center, use the two adjustment buttons on the outside of the condenser to adjust it. When the bright spot is adjusted to the center of the field, turn it up again to observe.
3. Precautions
① The numerical aperture of the objective lens used for dark field observation should be around 1.00-1.25. If it is too high, the effect may not be good. It is best to use an objective lens with a field of view aperture, and rotate the adjustment ring in the middle of the animal lens to freely change the size of the numerical aperture.
② The required slide and cover glass must be scratch free and dust-free, and the front lens of the objective lens must also be clean and dust-free. The thickness of the slide and cover glass should meet the standard. If the slide is too thick, the focus of the condenser will fall inside the slide and cannot reach the plane of the object being tested; When using an oil lens, due to the short working distance of the objective lens, it is even impossible to focus, resulting in the inability to see or clearly see the object being tested.
③ During mirror inspection, the room should be dark. If such conditions do not exist, shading devices should be used as much as possible to prevent light from entering the area around the eyepiece.
④ When conducting oil mirror inspection, due to the diffuse reflection of impurities and bubbles in the oil, it is required to remove as much impurities and bubbles as possible from the oil, which can hinder the inspection effect of the field of view
