Because the opening angle of the same object to the eye is related to the distance between the object and the eye, the magnification of the image at a distance of 25 cm (apparent distance) from the eye is generally specified as the magnification of the instrument. When observing an object with a microscope, the viewing angle is usually very small, so the ratio of viewing angles can be replaced by the ratio of tangents.
Extended data
Optical parts structure:
(1) spectacle lens: it is installed at the upper end of the lens barrel, and usually has 2-3 eyepieces, on which symbols of 5×, 10× or 15× are engraved to indicate its magnification. General installation 10× eyepiece.
(2) Objective lens: installed on the rotating body at the lower end of the lens barrel, there are generally 3-4 objective lenses, of which the shortest one engraved with the symbol "10X" is a low-power mirror, the longer one engraved with the symbol "40X" is a high-power mirror, and the longest one engraved with the symbol "10x" is an oil mirror. Besides,
The magnification of microscope is the product of the magnification of objective lens and the magnification of eyepiece. For example, if the objective lens is 10× the eyepiece is 10×, the magnification is10×/kloc-0 =100.
The length of microscope eyepiece is negatively correlated with magnification, and the length of objective lens is positively correlated with magnification. That is, the longer the eyepiece length, the lower the magnification; The longer the length of the objective lens, the higher the magnification.
Baidu encyclopedia-optical microscope
Baidu encyclopedia-microscope