First, the definition of optical microscope
Microscope is a precise optical instrument with a history of more than 300 years. Since the appearance of the microscope, people have seen many tiny creatures and cells, which are the basic units of organisms and were invisible in the past.
There are not only optical microscopes with a magnification of more than 1000 times, but also electron microscopes with a magnification of several hundred thousand times, which makes us have a further understanding of the law of life activities of organisms. Most of the experimental observation work is done by microscope, so the performance of microscope is the key to do a good job of observation experiment.
Second, historical development.
As early as the first century BC, people have found that when observing tiny objects through spherical transparent objects, the images can be enlarged. Later, I gradually realized that the surface energy of spherical glass magnifies the image of an object. In 1590, Dutch and Italian glasses manufacturers have built magnifying instruments similar to microscopes.
About 16 10 years ago, Galileo of Italy and Kepler of Germany changed the distance between the objective lens and the eyepiece and obtained a reasonable optical path structure of the microscope. At that time, optical craftsmen were engaged in the manufacture, promotion and improvement of microscopes.
Classification and main parameters of objective lens
1, classification of objective lens
The objective lens can be divided into dry objective lens and immersion objective lens according to different use conditions; Among them, immersion objective lens can be divided into immersion objective lens and oil-immersed objective lens (the common magnification is 90–100 times).
According to the different magnification, it can be divided into low-power objective (10 times or less), medium-power objective (about 20 times) and high-power objective (40-65 times).
According to aberration correction, it can be divided into achromatic objective lens (commonly used, which can correct the chromatic aberration of two colors in the spectrum) and apochromatic objective lens (which can correct the chromatic aberration of three colors in the spectrum, which is expensive and rarely used).
2. Main parameters of objective lens
The main parameters of the objective lens include magnification, numerical aperture and working distance.
(1) Magnification refers to the ratio of the size of the image seen by the eyes to the size of the corresponding specimen. It refers to the ratio of length, not the ratio of area. Example: The magnification is 100×, which refers to the specimen with the length of 1 μ m, and the length of the magnified image is100 μ m. If calculated by area, the magnification is 10000 times.
The total magnification of the microscope is equal to the product of the magnification of the objective lens and the eyepiece.
(2) Numerical aperture, also called aperture ratio, abbreviated as NA or A, is the main parameter of objective lens and condenser, which is directly proportional to the resolution of microscope. The numerical aperture of dry objective lens is 0.05–0.95, and the numerical aperture of oil-immersed objective lens (fragrant asphalt) is 1.25.
(3) The working distance refers to the distance from the lower part of the front lens of the objective lens to the upper part of the specimen cover glass when the specimen is most clearly observed.