The numerical aperture of the microscope
Numerical aperture is abbreviated as NA. Numerical aperture is the main technical parameter of objective lens and condenser lens, and it is an important indicator to judge the performance of both (especially for objective lens). The size of its numerical value is marked on the shell of the objective lens and the condenser lens respectively.
Numerical aperture (NA) is the product of the refractive index (n) of the medium between the front lens of the objective and the object to be inspected and the sine of half the aperture angle (u). The formula is expressed as follows: NA=nsinu/2
Aperture angle, also known as "mirror angle", is the angle formed by the object point on the optical axis of the objective lens and the effective diameter of the front lens of the objective lens. The larger the aperture angle, the brighter the light entering the objective, which is proportional to the effective diameter of the objective and inversely proportional to the distance from the focal point.
In microscope observation, if you want to increase the NA value, the aperture angle cannot be increased, and the only way is to increase the refractive index n value of the medium. Based on this principle, the water immersion objective lens and the oil immersion objective lens are produced. Since the refractive index n of the medium is greater than 1, the NA value can be greater than 1.
