Explanation of the structure of the illumination part of an optical microscope
It is installed below the stage and consists of a reflector (or light source), a condenser, and an aperture.
1) Reflector: Early optical microscopes used natural light to examine objects, and a reflector was installed on the mirror base. A reflector is a mirror composed of a flat surface and another concave surface, which can reflect the light projected on it onto the condenser lens for illuminating the specimen. A concave mirror can also be used to focus light. Modern optical microscopes generally use electric light sources, no reflective mirrors, and can adjust the intensity of light.
2) Concentrator: The condenser is located below the stage and is composed of a set of condensing lenses and lifting screws. The condenser is installed under the stage, and its function is to focus the light reflected by the light source through the reflector on the sample, in order to obtain the strongest illumination and achieve a bright and clear effect on the object image. The height of the condenser can be adjusted so that the focus falls on the object being tested to obtain maximum brightness. The focus of a general condenser is 1.25mm above it, and its lifting limit is 0.1mm below the plane of the stage. Therefore, it is required that the thickness of the glass slide used should be between 0.8~1.2mm, otherwise the tested sample is not in the focal point, which affects the microscopic inspection effect.
3) Aperture: There is also a rainbow aperture in front of the front lens group of the condenser, which can be opened and closed to control the amount of light passing through, thereby affecting the resolution and contrast of imaging. If the rainbow aperture is opened too large, exceeding the numerical aperture of the objective lens, a light spot is generated; If the iris aperture is too small, the resolution decreases and the contrast increases. Therefore, during observation, by adjusting the iris aperture, the field of view aperture (microscope with field of view aperture) is opened to the outer tangent of the perimeter of the field of view, so that no light can be illuminated outside the field of view to avoid interference from scattered light.
