What is the principle of lens imaging? What is the imaging principle of a convex lens?

The imaging law of convex lens is one of the compulsory test points in the high school entrance examination.

The principle of convex lens imaging is a magnifying glass and microscope made of the principle of refraction of light and the principle of linear propagation of light, which is used to observe objects that should be magnified when placed near the observer. The optical lens made of glass or other transparent materials with a curved surface can magnify the object, the imaging principle of the magnifying glass, the object AB within F, its size is Y, and it is magnified by the magnifying glass into a size Y'The virtual image of A'b'。Magnification of the magnifier = 250 f'where 250 - photopic distance, the unit is mm f'--Magnifier focal length, in mm This magnification refers to the ratio of the angle of view of the object image observed with a magnifying glass to the angle of view of an object observed without a magnifying glass at a distance of 250mm.

Transmission electron microscopy, also known as transmission electron microscopy, is a type of electron microscope. Electron microscope is a high-precision electron optical instrument, which has high resolution ability and magnification, and is an important tool for observing and studying the microstructure of matter.

Electron microscope is an instrument that replaces light beams and optical lenses with electron beams and electron lenses according to the principle of electron optics to image the fine structure of matter at very high magnification. The resolving power of an electron microscope is expressed in terms of the minimum distance between two adjacent points that it can resolve. In the 70s of the 20th century, the resolution of transmission electron microscopy was about nanometers (the resolution of the human eye was about millimeters).

At present, the maximum magnification of electron microscopes is more than 3 million times, while the maximum magnification of optical microscopes is about 2000 times, so it is possible to directly observe the atoms of certain heavy metals and the neatly arranged atomic lattices in crystals through electron microscopes.

In 1931, Knorr-Bremse and Ruska in Germany modified a high-voltage oscilloscope with a cold cathode discharge electron source and three electron lenses, and obtained images magnified more than ten times, confirming the possibility of electron microscope magnification. In 1932, after Ruska's improvement, the resolution of the electron microscope reached 50 nanometers, which was about ten times the resolution of the optical microscope at that time, so the electron microscope began to attract people's attention. In the 40s of the twentieth century, Hill of the United States used an image dispersion device to compensate for the rotational asymmetry of the electron lens, which made a new breakthrough in the resolving ability of the electron microscope and gradually reached the modern level.

In China, a transmission electron microscope was successfully developed in 1958 with a resolution of 3 nanometers, and in 1979, a large electron microscope with a resolution of nanometers was made.

Although the resolution of electron microscopes is far superior to that of optical microscopes, electron microscopes are difficult to observe living organisms because they need to work under vacuum conditions, and biological samples can also be damaged by irradiation due to the irradiation of electron beams. Other issues, such as the improvement of the brightness of the electron gun and the quality of the electronic lens, also need to be further studied.

The imaging principle of transmission electron microscopy is that the electron beam with a certain aperture angle and intensity provided by the illuminated part is projected parallel to the sample at the plane of the objective lens, and the diffraction amplitude maximum is formed on the rear focal plane of the objective lens through the electron beam of the sample and the objective lens, that is, the first diffraction spectrum. These diffraction beams interfere with each other in the image plane of the objective to form the first electronic image that reflects the micro-characteristics of the specimen. By focusing (adjusting the excitation current of the objective lens), the image plane of the objective lens is consistent with the object plane of the intermediate mirror, the image plane of the intermediate mirror is consistent with the object plane of the projection mirror, and the image plane of the projection mirror is consistent with the fluorescent screen, so that an electronic image with a certain contrast and magnification after magnification by the objective lens, the intermediate mirror and the projection mirror can be observed on the fluorescent screen.

Due to the difference in the thickness, atomic number, crystal structure or crystal orientation of each microregion of the sample, the electron beam intensity of the specimen and the objective lens is different, so the microscopic electron image of the micro-area characteristics of the specimen reflected by the difference between dark and light is displayed on the phosphor screen. The magnification of an electronic image is the magnification of the objective, intermediate, and projection mirrors.

Transmission electron microscope is a high-resolution, high-magnification electron-optical instrument that uses an electron beam with a very short wavelength as the illumination source to focus the imaging with an electromagnetic lens. Transmission electron microscopy projects an accelerated and concentrated beam of electrons onto a very thin sample (sheet< 100 nm, particle < 2 um), and the electrons collide with the atoms in the sample and change direction, resulting in solid angle scattering. **The difference in light and dark (black, white and gray) is related to the atomic number, electron density, thickness and other aspects of the sample.

The imaging method is similar to that of an optical microscope, except that electrons are used instead of photons, electromagnetic lenses are used instead of glass lenses, and the magnified electron image is displayed on a phosphor screen.

Transmission electron microscopy is classified according to the accelerating voltage, which can usually be divided into conventional electron microscopy (100kV), high-voltage electron microscope (300kV) and ultra-high-voltage electron microscope (above 500kV). Increasing the acceleration voltage can increase the energy of the incident electrons, which is conducive to improving the resolution of the electron microscope on the one hand. At the same time, it can improve the ability to penetrate the specimen.

Transmission electron microscopy (TEM) projects an accelerated and concentrated beam of electrons onto a very thin sample, and the electrons collide with the atoms in the sample and change direction, resulting in solid angle scattering. The magnitude of the scattering angle is related to the density and thickness of the sample, so that different light and dark images can be formed, and the images will be magnified and focused and displayed on imaging devices such as phosphor screens, films, and photosensitive coupling components.

The principle of transmission electron microscopy imaging, because the de Broglie wavelength of electrons is very short, the resolution of transmission electron microscope is much higher than that of optical microscope, and the magnification can be tens of millions of times. Therefore, the use of TEM can be used to observe the fine structure of a sample, even a column of atoms, tens of thousands of times smaller than the z-smallest structure that can be observed with an optical microscope. TEM is an important analytical method in many scientific fields related to physics and biology, such as cancer research, virology, materials science, as well as nanotechnology, semiconductor research, and so on.

When the magnification is low, the contrast of transmission electron microscopy imaging is mainly caused by the different thickness and composition of the material. However, when the magnification is high, the complex fluctuation will cause the brightness of the image to differ, so specialized knowledge is required to analyze the obtained image. By using the different modes of TEM, the sample can be imaged by the chemical properties of the substance, the crystal orientation, the electronic structure, the electron phase shift caused by the sample, and the usual electron absorption.

The imaging principle of transmission electron microscopy can be divided into three cases:

Absorption image: When electrons are emitted to a massive, dense sample, the main phase formation is scattering. The scattering angle of electrons on the sample is large where the mass thickness is large, fewer electrons pass through, and the brightness of the image is darker. Early TEMs were based on this principle.

Diffraction image: After the electron beam is diffracted by the sample, the amplitude distribution of the diffracted wave at different positions of the sample corresponds to the different diffraction ability of each part of the crystal in the sample, and when the crystal defect appears, the diffraction ability of the defective part is different from that of the complete area, so that the amplitude distribution of the diffracted wave is uneven, reflecting the distribution of crystal defects.

Phase image: When the sample is less than 100 thin, electrons can pass through the sample, the amplitude change of the wave is negligible, and the imaging comes from the change in phase.

The incident light is emitted from the luminous point S, and after being refracted by a convex lens, the refracted rays converge to form the image S of the luminous point S'There are three important rays of light when making a light path diagram:

1) The incident ray parallel to the main optical axis of the convex lens, after being refracted by the convex lens, the refracted light is emitted through the focal point on the other side of the convex lens;

2) The incident ray passing through the optical center of the convex lens, after being refracted by the convex lens, the refracted light keeps the original direction of incidence unchanged and is emitted from the other side of the convex lens;

3) The incident light passing through the focal point on one side of the convex lens, after being refracted by the convex lens, the refracted light rays are emitted from the other side of the convex lens parallel to the main optical axis.

The specific optical path diagram is as follows:

Convex lens imaging principle: the object is placed outside the focus, and the other side of the convex lens becomes an inverted real image, and the real image has three types: reduction, equal size, and magnification. The smaller the object distance, the larger the image distance, and the larger the real image. The object is placed in focus, and the virtual image is magnified upright on the same side of the convex lens.

The larger the object distance, the larger the image distance, and the larger the virtual image. No imaging when in focus. At 2x focal length, it will be an inverted real image.

In optics, the image formed by the convergence of actual light is called a real image, which can be undertaken by an optical screen; Otherwise, it is called an illusion and can only be perceived by the eyes. Experienced physics teachers, when talking about the difference between real and virtual images, often mention such a way to distinguish between real and virtual images: "Real images are inverted, while virtual images are upright."

Optical microscopes and telescopes (including some astronomical telescopes) are made using the principle of refraction of light and the straight-line propagation of light. Magnifiers and microscopes are convex lenses used to observe objects placed in close proximity to the observer that should be magnified.

Microscopes and magnifying glasses serve the same purpose, that is, to make a magnified image of a small object in the near distance for the human eye to observe. It's just that a microscope can have a higher magnification than a magnifying glass.

Imaging principles and applications of convex lenses:

Object distance (u) Nature of image Image distance (v) Application example.

u > 2f handstand, zoomed out, real image f 2f slide projector.

u = f does not image --

u < f upright, magnifying, virtual image v > u magnifying glass, reading glasses.

I hope it helps you, and if you have any questions, you can ask them

I wish you progress in your studies and go to the next level! (*

The imaging law of convex lens is one of the compulsory test points in the high school entrance examination.

The imaging principle of a convex lens is that light travels in a straight line.

In the actual environment of this kind of optics, the data analysis of the imaging principle of this optical lens is generated.