What should users pay attention to when using a dark field microscope
1. When making a dark field light barrier, if the diameter of the light barrier is too small or the center position of the light barrier is not correct, it cannot completely block out direct light, the field of view is not dark, and the contrast between the sample and the background is not obvious; If the diameter of the light barrier is too large, the light focused on the sample is insufficient, resulting in poor brightness of the sample observed by the dark field microscope, which affects the observation effect.
2. When using a dark field microscope, the illumination intensity of the light source should be high, otherwise the reflected light intensity of the sample is not enough, which affects the observation effect.
3. If the contrast between the sample and the background in the field of view is not strong, the position of the spotlight can be adjusted up and down to increase the contrast in the field of view.
4. The required glass slides and cover slips 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 glass 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.
5. The numerical aperture of the objective lens must be smaller than the numerical aperture of the condenser, otherwise, due to the aperture angle of the objective lens being greater than the angle of the central dark area of the illumination beam formed by the condenser of the dark field microscope, some illumination light may enter the objective lens, damaging or reducing the illumination of the dark field.
6. The thickness of the glass slide should be appropriate. After the illumination beam passes through the concentrator of the dark field microscope, a hollow illumination cone is generated, with the center being the dark area. The focus of the reflected light is on the surface of the lens on the condenser, at a short distance. Therefore, the appropriate thickness for glass slides is 0.8-1.2mm.
7. When using a dark field microscope for examination, the room should be dark. If such conditions are not available, shading devices should be used as much as possible to prevent the light around the eyepiece from entering.
8. When conducting oil mirror inspection, due to the diffuse reflection of impurities and bubbles in the oil, it will hinder the inspection effect of the dark field microscope. Therefore, it is required to remove impurities and bubbles in the oil as much as possible.
