The structure of a metallographic microscope is mainly divided into three parts.
mechanical part
1. The mirror holder is the base of the entire metallographic microscope. It is usually horseshoe shaped or rectangular, used to support the smoothness of the entire mirror body. Some microscopes are equipped with illumination devices inside the mirror holder.
2 . The mirror post is the upright part above the mirror holder, used to connect and support the mirror arm.
3 . The mirror arm is the curved part of the mirror column facing upwards. Some microscopes held during use have a movable joint called the tilt joint between the mirror arm and the mirror holder. The mirror can be tilted backwards for easier observation.
4. A cylindrical tube connected to the front of the mirror arm, generally 160mm in length. Some tubes are fixed and immovable, while others can move up and down. An eyepiece is installed at the upper end of the tube, and an objective converter is connected at the lower end.
5. The adjuster is a spiral of two sizes installed on the mirror arm or column. When rotated, it can move the lens barrel or stage up and down to adjust the distance between the objective lens and the specimen, that is, to adjust the focal length. When the coarse adjustment screw rotates, the range of up and down movement is large, which can quickly adjust the distance between the objective lens and the specimen to present the object image in the field of view. When the fine adjustment screw rotates, the amplitude of up and down movement is small. Generally, on the basis of using the coarse adjustment screw for focusing or when using a high-power lens, it is used for comparative adjustment to obtain a completely clear object image and to observe the structure of the specimen at different levels and depths.
6. The objective lens converter (rotating disc) is connected to a freely rotatable disc at the lower end of the lens barrel, and has
3-4 circular holes, the objective lens is installed in these circular holes, and rotating the rotating disc can exchange the objective lens with different magnifications. When the objective lens is rotated to the working position (i.e. aligned with the optical axis), it is necessary to fasten the notch on the edge of the rotating disc to the fixed buckle on the base, otherwise the specimen cannot be observed.
7. The metallographic microscope stage is a square or circular platform located below the lens barrel, used to place glass slide specimens. There is a circular light hole in the center of the platform, through which light from below shines onto the specimen. The stage is equipped with a specimen pusher, and the curved spring clip on the left side is used to fix the specimen. By rotating the two screws on the right side, the specimen can be moved forward, backward, left, and right. Some thrusters also have scales on them, which can calculate the distance traveled by the specimen and determine its position.
Lighting section
1. A reflector is a double-sided mirror with one side flat and the other side concave, installed at the base of the mirror holder and can rotate in any direction. Its function is to change the direction of the light source and reflect it onto the collecting mirror, and then illuminate the specimen through the light hole. The concave surface of a reflector has strong focusing power and is suitable for use in low light conditions. When the light is strong, a flat mirror is recommended.
2. A collector, also known as a condenser, is located on a bracket below the stage and consists of a collector mirror and an iris aperture. The adjustment screw under the mirror platform can be used to control its lifting and lowering, in order to adjust the strength of the light.
Optical part
1. Eyepiece, also known as eyepiece, is installed at the upper end of the lens barrel and usually consists of two lenses. There is a metal diaphragm installed between the upper and lower lenses or below the lower lens, which determines the size of the field of view, hence it is called a field diaphragm. An eyepiece micrometer can also be installed on the surface of the aperture, and a pointer can be attached to the aperture using human hair to indicate the observation target. A microscope usually has 2-3 eyepieces engraved with symbols such as 5x, 10x, 15x to indicate its magnification, which can be selected for use. The commonly used eyepiece magnification is 10x.
2. The objective lens, also known as the connecting objective lens, is mounted on the objective lens converter and generally has 3-4 lenses. The objective lens is a set of lenses consisting of several convex and concave lenses, which are strictly combined. It is a key component for determining the resolution performance of a microscope. Usually, the main performance indicators are marked on the objective lens - magnification and aperture ratio (such as 10/0.25, 40/0.65, and 100/1.25), barrel length, and required cover glass thickness (such as 160/0.17). According to different magnification factors, it is customary to refer to lenses below 10 times as low magnification lenses, lenses below 40 times as high magnification lenses, and oil immersion lenses at 90 or 100 times as oil immersion lenses. For easy differentiation, a circle of different colored lines is commonly used as a special symbol on high magnification mirrors and oil mirrors.
