How to read the magnification of the eyepiece and objective lens 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 lens. For example, if the objective lens is 10 x and the eyepiece lens is 10 x, the magnification is 10 x 10=100.
One objective lens:
1. Classification of objective lenses:
Objective lenses can be divided into dry objectives and immersion objectives according to different usage conditions; Among them, immersion lenses can be divided into water immersion lenses and oil immersion lenses (commonly used magnification is 90-100 times).
According to different magnification factors, it can be divided into low magnification objectives (below 10x), medium magnification objectives (around 20x), and high magnification objectives (40-65x).
According to the aberration correction situation, it is divided into achromatic objective lenses (commonly used, which can correct the color difference of two colors in the spectrum) and chromatic aberration objective lenses (which can correct the color difference of three colors in the spectrum, 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 eyes to the corresponding specimen size. It refers to the ratio of length rather than the ratio of area. Example: A magnification of 100 times refers to a specimen with a length of 1 μ m. The length of the magnified image is 100 μ m. If calculated by area, it is magnified 10000 times.
The total magnification of a microscope is equal to the product of the magnification of the objective lens and eyepiece lens.
② Numerical aperture, also known as aperture ratio, abbreviated as NA or A, is the main parameter of the objective lens and condenser, directly proportional to the resolution of the microscope. The numerical aperture of the dry objective lens is 0.05-0.95, and the numerical aperture of the oil immersed objective lens (cedarwood 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 observed specimen is at its clearest. The working distance of the objective lens is related to its focal length. The longer the focal length of the objective lens and the lower the magnification, the longer its working distance. Example: The 10x objective lens is marked with 10/0.25 and 160/0.17, where 10 is the magnification of the objective lens; 0.25 is the numerical aperture; 160 is the length of the lens barrel (in millimeters); 0.17 is the standard thickness of cover glass (in millimeters). The effective working distance of a 10x objective lens is 6.5mm, and the effective working distance of a 40x objective lens is 0.48mm.
