Introduction to the function of optical microscope variable aperture
Variable aperture, also known as aperture, is located below the condenser lens and consists of more than ten thin metal sheets, with a circular hole formed in the center. Its function is to adjust the light intensity and make the numerical aperture of the condenser lens compatible with the numerical aperture of the objective lens. The larger the aperture of the variable aperture, the larger the numerical aperture (after observation, the aperture should be adjusted to the maximum).
Under the variable aperture, there is also a circular filter holder.
Explanation: In high school laboratories, only teachers use microscopes (1600 × or 1500 ×) equipped with concentrators, while students use microscopes (640 × or 500 ×) equipped with rotating light bars. A circular disk that can rotate in a circular motion and is tightly attached to the stage. The rotating light bar (also known as a shutter) has circular holes of varying sizes on the light bar, called aperture. The diameters are 2, 3, 6, 12, and 16mm respectively. By rotating the light bar, each aperture on the light bar can be aligned with the light hole, and the intensity of the light can be adjusted by varying the size of the aperture.
What is the optical principle (bright field, dark field) of a metallographic microscope? The main characteristics of a bright field are based on the color and transmittance of the specimen, which usually requires staining for easy observation. Of course, reducing the aperture or upper and lower concentrators can also be used. The bright field is the foundation of all other optical microscopes. Dark field is a method designed based on the principle of the Tyndall effect to observe and detect objects in a dark background. Under normal conditions, people cannot see indoor dust because dust particles are interfered by factors such as direct sunlight and diffraction. However, if light passes through a window in a dark indoor environment, we can easily see it because when light reflects or diffracts, fine dust particles seem to increase in volume. Dark field refers to the use of special methods to prevent direct light from entering the objective lens. Instead, the direct light passes through a dark field condenser and changes its path, causing it to obliquely enter the object being measured. The surface produces reflected or diffracted light that enters the objective lens, forming a bright image with a background in the dark
