China Microscope - Wang Liang: 010-82967128 13910386343 The basic optical principle of the microscope
Basic optical principle of a microscope Dried Garlic Products,Dried Garlic Flakes,Dried Garlic Puree,Dried Garlic Slice Huaiyang County Wanyuan Garlic Foods Processing Industries Co.,Ltd , https://www.wanyuangarlicfood.com
(1) Refraction and refractive index
Light is transmitted in a uniform isotropic medium in a straight line between two points. When passing through transparent objects of different density medium, refraction occurs due to the different propagation speeds of light in different media. When light that is not perpendicular to the transparent object is incident on a transparent object (such as glass) by air, the light changes direction at its interface and forms a refraction angle with the normal.
(two) the performance of the lens
The lens is the basic optical component of the Zui that constitutes the microscope optical system, and the components such as the objective lens and the condensing mirror are composed of single and multiple lenses. Depending on its shape, it can be divided into convex lens (positive lens) and concave lens (negative lens).
When a beam of light parallel to the optical axis passes through the convex lens and intersects at a point, this point is called the "focus", passing through the intersection and perpendicular to the plane of the optical axis, called the "focal plane". There are two focal points, the focus of the object space, called the "object focus", the focal plane of the object, called the "object focal plane"; conversely, the focus of the image space, called the "image focus", The focal plane at the point is called "image square focal plane".
After the light passes through the concave lens, it becomes an erect virtual image, and the convex lens becomes an erect real image. The real image can appear on the screen, and the virtual image cannot.
(III) Five imaging laws of convex lenses
1. When the object is located outside the focal length of the lens object, a reduced inverted real image is formed within the focal length of the image and beyond the focus;
2. When the object is located at twice the focal length of the object of the lens, an inverted image of the same size is formed on the image twice the focal length;
3. When the object is located within twice the focal length of the object of the lens, and outside the focus, an enlarged inverted real image is formed outside the focal length of the image;
4. When the object is located at the focal point of the object of the lens, then the image cannot be imaged;
5. When the object is located within the focus of the object of the lens, then the image is formed without image, and an enlarged erect virtual image is formed at a position farther from the object on the same side of the object.
Third, the optical microscope imaging (geometric imaging) principle
Only when the opening angle of the object to the human eye is not less than a certain value, the naked eye can distinguish its various details, which is called the visual resolution ε. Under the good condition of Zui, that is, the illuminance of the object is 50~70lx and the contrast is large, it can reach 1'. For ease of observation, this amount is generally increased to 2' and taken as the average eyepiece resolution.
The size of the object's viewing angle is related to the length of the object and the distance from the object to the eye. There is a formula y=Lε
The distance L cannot be made small because there is a limit to the adjustment ability of the eye, especially when the eye is working close to the limit of the adjustment ability, the vision is extremely fatigued. For the standard (front view), Zui's line of sight is specified to be 250 mm (clear viewing distance). This means that in the absence of an instrument, an eye with a visual resolution of ε = 2' can clearly distinguish the details of an object with a size of 0.15 mm.
When observing an object with a viewing angle of less than 1', an amplifying instrument must be used. Magnifiers and microscopes are used to observe objects placed in the vicinity of the observer.
(1) Imaging principle of magnifying glass
An optical lens made of curved glass or other transparent material can magnify and image the object. The optical path diagram is shown in Figure 1. The object AB, located within the object focus F, has a size of y, which is magnified by a magnifying glass into a virtual image A'B' of size y'.
Magnifying glass magnification
Γ=250/f'
250--the apparent distance, in mm
f'--Magnifying glass focal length in mm
The magnification refers to the ratio of the angle of view of the object image observed with a magnifying glass within a distance of 250 mm to the angle of view of the object observed without the magnifying glass.
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Optical microscope composition The optical microscope generally consists of a stage, a concentrated illumination system, an objective lens, an eyepiece and a focusing mechanism. The stage is used to hold the object being observed. The focusing knob can be used to drive the focusing mechanism, so that the stage can be coarsely adjusted and fine-tuned, so that the observed object can be clearly imaged. Its upper layer can be precisely moved and rotated in the horizontal plane, and the observed part is generally placed in the center of the field of view.
The concentrating illumination system consists of a light source and a concentrating mirror. The function of the concentrating mirror is to concentrate more light energy on the observed part. The spectral characteristics of the illuminator must be compatible with the operating band of the microscope's receiver.
The objective lens is located near the object to be observed and is a lens that achieves * level magnification. The objective lens converter is equipped with several objective lenses of different magnifications at the same time. Rotating the converter allows the objective lenses of different magnifications to enter the working optical path, and the magnification of the objective lens is usually 5 to 100 times.
The objective lens is an optical component that plays a decisive role in the quality of the image in the microscope. Commonly used are achromatic objectives that can correct the chromatic aberration of the two colors; the higher quality is the apochromatic objective lens which can correct the chromatic aberration of the three color lights; the entire image plane of the objective lens can be ensured to improve the field of view. Flat image field objective for edge imaging quality. In the high-power objective lens, an immersion objective lens is used, that is, a liquid having a refractive index of about 1.5 is filled between the lower surface of the objective lens and the upper surface of the specimen sheet, which can significantly improve the resolution of microscopic observation.
The eyepiece is a lens that achieves second-level magnification near the human eye. The magnification of the mirror is usually 5 to 20 times. According to the size of the field of view that can be seen, the eyepiece can be divided into two types: the ordinary eyepiece with a small field of view and the large field of view eyepiece (or wide-angle eyepiece) with a larger field of view.
Both the stage and the objective lens must be able to move relative to each other along the optical axis of the objective lens to achieve focusing and obtain a clear image. When working with a high power objective, the allowable focusing range is often less than micrometers, so the microscope must have an extremely precise micro-focusing mechanism.
The limit of the magnification of the microscope is the effective magnification. The resolution of the microscope refers to the small spacing of the two points that can be clearly distinguished by the microscope. Resolution and magnification are two different but different concepts.
When the selected numerical aperture of the objective lens is not large enough, that is, the resolution is not high enough, the microscope cannot distinguish the fine structure of the object. Even if the magnification is excessively increased, only an image with large outline but unclear details can be obtained. , called invalid magnification. On the other hand, if the resolution is sufficient and the magnification is insufficient, the microscope has the ability to distinguish, but the image is too small to be clearly seen by the human eye. Therefore, in order to give full play to the resolving power of the microscope, the numerical aperture should be reasonably matched with the total magnification of the microscope.
The concentrating illumination system has a great influence on the imaging performance of the microscope, but it is also a part that is easily overlooked by the user. Its function is to provide a sufficient and uniform surface illumination. The beam from the condenser should be able to fill the aperture angle of the objective lens, otherwise the high resolution of the Zui can be fully utilized. For this purpose, a variable aperture stop, similar in photographic objectives, that adjusts the size of the opening, is provided in the concentrating mirror for adjusting the illumination beam aperture to match the aperture angle of the objective lens.
By changing the way of illumination, you can get different observations such as dark objects on a bright background (called bright field illumination) or bright points on a dark background (called dark field illumination) to better find in different situations. And observe the fine structure.