It has no discriminating effect, just a magnifying glass in the microscope optical system. It enlarges the object image that has been enlarged and identified by the objective lens once again, making it easier to observe. Its basic structure is composed of 2 or 2 groups of lenses, divided into upper and lower parts. It is installed in a metal tube, as shown in Figure 3-lo. The upper lens (that is, the lens close to the eye) is called the eyepiece or active lens (also called the eyepiece); the factory lens is called the field lens (or the field lens, because it faces the field of view) or collection Mirror refers to its function of collecting preliminary object images from the field of view, also known as a negative lens. The magnification of the eyepiece is directly marked with the â€œÃ—â€ symbol (that is, the magnification). Generally there are: 4 Ã—, 5 Ã—, 6 Ã—, 8 Ã—, 10 Ã—, 12 Ã—, 15 Ã—, 16 Ã—, etc. But this is not fixed, it is mainly determined according to the needs and production conditions.
Three functions of the field lens in the eyepiece:
1. After the objective lens sent from the objective lens is concentrated by the field lens, it can be slightly tightened to increase its brightness; and the light at the edge of the field of view can be concentrated to the center to eliminate its aberration and chromatic aberration.
2. Cooperate with eyepiece to correct aberration and chromatic aberration.
3. It can correct the expansion distortion caused by receiving the objective lens.
Classification of eyepieces: According to the path of light, there are two categories:
1. Positive eyepieces. The positive eyepiece is characterized by the convex face of the eyepiece and the field lens. This eyepiece can be used as a kind of eyepiece for magnifying glass alone. The initial magnified image from the field of view first falls under the field lens, just like a simple magnifying glass. This type of positive eyepiece is often used for optical instruments for measurement, and sometimes for simple dissecting microscopes.
2. Negative eyepiece. It cannot be used alone as a magnifying glass, because the object image from the field of view falls between the eyepiece and the field lens, so it must be used in conjunction with the objective lens to see the object image. It is characterized by the co-directional field of view of the convex surface of the eyepiece and field lens.
There are generally four types of negative eyepieces: one is the Haigeng type eyepiece. The focal point of the field lens is generally 3 times that of the eyepiece. In order to eliminate chromatic aberration, the distance between the two lenses is installed at the average of the two focal points, that is, this arrangement causes the object image to fall within the focal point of the eyepiece.
The other is the positive format eyepieces. Neither the positive drawing eyepieces nor the Geng type eyepieces can be equipped with pointers. If the magnification is more than 10 times, the distance of the eye point is shorter, and it is more inconvenient to observe the object image, especially wearing glasses People.
The other two are compensating eyepieces and periscope lenses. As mentioned earlier, the eyepiece can correct the aberration and chromatic aberration caused by the objective lens. If a single lens is replaced by a double compound lens, but the field lens is still a single lens, the result is that The entire eyepiece has a large chromatic aberration and aberration, so it offsets the error caused by the objective lens, so it is called the compensation eyepiece. To know whether the eyepiece is a compensation interface lens, the simplest method is to put the eyepiece in front of your eyes to observe the sky or pane. If you find an orange edge, it is the compensation eyepiece, otherwise it is not.
In order to easily distinguish various eyepieces, they are all marked on the edge of the eyepiece frame, and also indicate the magnification of the eyepieces.
The code name of the domestic eyepiece:
Compensating eyepiece Bc
Flat field eyepiece PC
Wide Angle Eyepiece GJ
Projection eyepiece w
Photography eyepiece SY
Binocular eyepiece ST
Code for eyepieces of foreign products:
Haigeng Eyepiece H
Positive eyepiece o
Compensation eyepiece K
Plane eyepiece P
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