Function introduction of optical microscope iris diaphragm
The variable diaphragm, also called the aperture, is located below the condenser and consists of more than a dozen metal sheets with a round hole in the center. Its function is to adjust the light intensity and adapt the numerical aperture of the condenser to the numerical aperture of the objective lens. The wider the iris is opened, the larger the numerical aperture (after observation, the aperture should be adjusted to the maximum).
Below the iris diaphragm, there is also a circular filter holder.
Note: In middle school laboratories, only teacher microscopes (1600× or 1500×) are equipped with condensers, while student microscopes (640× or 500×) are equipped with rotating diaphragms. It is a disc that can rotate in a circle and is placed closely under the stage. It is a rotating diaphragm (also called a shutter). There are round holes of different sizes on the diaphragm, which are called apertures. The diameters are 2, 3, 6, 12, and 16mm respectively. Turn the rotating diaphragm. Each aperture on the diaphragm can be aligned with the light hole, and the intensity of the light can be adjusted through apertures of different sizes.
What are the optical principles (bright field, dark field) of metallographic microscopes?
The main characteristics of bright field are based on the color and transmittance of the specimen. The specimen usually needs to be dyed to facilitate observation. Of course, narrowing the aperture or upper and lower condensers can also be used. Brightfield is the basis for all other optical microscopy. Dark field is a method designed based on the Tyndall effect principle to observe detection objects under dark background conditions. Under normal conditions, people cannot see indoor dust. This is because dust particles are exposed to strong direct light and diffraction. Interference But if we let the light pass through the window in dark indoor conditions, we can easily see it. This is because when the light is reflected or diffracted, the dust particles seem to increase in size. Dark field is a lens that uses a special method to prevent direct light from entering the objective lens. Instead, the direct light first passes through the dark field condenser and then changes its path so that it enters the object being measured obliquely. The surface reflects or diffracts the light into the objective lens to form a print on the object. Bright image on dark background
