What is the magnification of the eyepiece and objective of an optical microscope
The magnification of an optical microscope is the product of the magnification of the objective lens and the magnification of the eyepiece, such as the objective lens being 10 ×， Eyepiece is 10 ×， Its magnification is 10 × 10=100.
Objective:
1. Classification of objective lenses:
Objective lenses can be divided into dry objective lenses and immersion objective lenses according to different usage conditions; The immersion objective can also be divided into water immersion objective and oil immersion objective (commonly used magnification is 90-100 times).
According to the different magnifications, it can be divided into low magnification objectives (below 10x), medium magnification objectives (around 20x), and high magnification objectives (40-65x).
According to the situation of aberration correction, it is divided into achromatic objective lenses (commonly used, objective lenses that can correct the color difference of two colors of light in the spectrum) and polychromatic objective lenses (objective lenses that can correct the color difference of three colors of light in the spectrum, which are expensive and rarely used).
2. Main parameters of the 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 eye to the size of the corresponding specimen. It refers to the ratio of length rather than the ratio of area. Example: Magnification factor of 100 ×， Refers to a length of 1 μ The length of the magnified specimen of m is 100 μ m. If calculated by area, it is magnified by 10000 times.
The total magnification of a microscope is equal to the product of the magnification of the objective and eyepiece.
② Numerical aperture, also known as aperture ratio, abbreviated as NA or A, is the main parameter of the objective lens and condenser, which is directly proportional to the resolution of the microscope. The numerical aperture of the dry objective is 0.05-0.95, and the numerical aperture of the oil immersed objective (cedar oil) is 1.25.
③ The working distance refers to the distance from the front lens of the objective lens to the cover glass of the specimen when the specimen is most clearly observed. The working distance of the objective lens is related to its focal length. The longer the focal length of the objective lens, the lower the magnification, and the longer its working distance. Example: A 10x objective is labeled with 10/0.25 and 160/0.17, where 10 is the magnification of the objective; 0.25 is the numerical aperture; 160 is the length of the lens tube (in mm); 0.17 is the standard thickness of the cover glass in millimeters. The effective working distance of a 10x objective is 6.5mm, and the effective working distance of a 40x objective is 0.48mm.
3. The function of the objective lens is to magnify the specimen for the first time, and it is the most important component that determines the performance of the microscope - the level of resolution.
Resolution is also known as resolution or resolving power. The magnitude of resolution is expressed by the numerical value of the resolution distance (the minimum distance between two object points that can be distinguished). At a clear distance of 25cm, two objects with a distance of 0.073mm can be clearly seen by the normal human eye. This value of 0.073mm is the resolution distance of the normal human eye. The smaller the resolution distance of a microscope, the higher its resolution and better its performance.
