What are the functions of microscope objective lens
The function of the objective lens is to magnify the specimen for the first time, and it is the most important part that determines the performance of the microscope - the resolution.
Resolution is also called resolution or resolving power. The size of the resolution is expressed by the value of the resolution distance (the minimum distance between two object points that can be resolved). At the photopic distance (25cm), normal human eyes can clearly see two object points that are 0.073mm apart. The value of 0.073mm is the resolution distance of normal human eyes. The smaller the resolution distance of the microscope, the higher its resolution, and the better its performance.
The size of the resolution of the microscope is determined by the resolution of the objective lens, and the resolution of the objective lens is determined by its numerical aperture and the wavelength of the illumination light.
When using the common central illumination method (the photopic illumination method that allows the light to pass through the specimen evenly), the resolution distance of the microscope is d=0.61λ/NA where d——the resolution distance of the objective lens, in nm. λ—wavelength of illumination light, unit nm. NA ——the numerical aperture of the objective lens, for example, the numerical aperture of the oil immersion objective lens is 1.25, and the visible light wavelength range is 400-700nm. If the average wavelength is 550 nm, then d=270 nm, which is about half the wavelength of the illumination light. In general, the limit of resolution of microscopes illuminated with visible light is 0.2 μm.
