1.Problem:Regarding ND18, How`s the NA (Numerical aperture) of the collimator lens, what kind of data does it represent?
2.Analysis:Numerical aperture, that is, clear aperture. The numerical aperture is the main technical parameter of the lens and the condenser, and it is important to judge the performance of both (especially for the objective lens) (that is, the ability to eliminate positional chromatic aberration, and Zeiss’s numerical aperture represents the ability to eliminate positional chromatic aberration and magnification). Sign. The numerical value is marked on the shell of the objective lens and condenser lens. The numerical aperture (NA) is the product of the refractive index (n) of the medium between the lens and the object to be inspected and the sine of the half of the aperture angle (2α). The formula is as follows: NA = n * sin α. The aperture angle, also known as the “lens aperture angle”, is the angle formed by the object point on the optical axis of the lens and the effective diameter of the front lens of the objective lens. The larger the aperture angle, the greater the luminous flux entering the lens, which is proportional to the effective diameter of the lens and inversely proportional to the distance of the focal point.