What is the purpose of the microscope objective lens?
Objective lens is the most important optical components of the microscope, the use of light to make the object being examined for the first time into the image, and therefore directly related to and affect the quality of the image and the optical technical parameters, is a measure of the quality of a microscope is the primary standard.
Objective lens structure is complex, precision production, usually by the combination of lens group, the lenses are separated from each other by a certain distance to reduce the phase difference. Each group of lenses is made of different materials, different parameters of one or several pieces of lenses glued together. Objective lenses have many specific requirements, such as co-axiality, focusing.
Modern microscope objective lens has reached a high degree of perfection, its numerical aperture is close to the limit, the resolution of the centre of the field of view and the difference between the theoretical value has been minimal. But continue to increase the field of view of the microscope objective lens and improve the image quality of the edge of the field of view of the possibility still exists, this research work, is still in progress.
Zifocal both in the mirror, when a certain magnification of the objective lens to observe the image is clear, in the conversion of another magnification of the objective lens, the image should be basically clear, and the centre of the elephant deviation should be within a certain range, that is, the degree of co-axial. The quality of the focusing performance and the degree of co-axiality is an important symbol of the quality of the microscope, which is related to the quality of the objective lens itself and the precision of the objective lens converter.
The aberrations related to the wide beam are spherical aberration, coma aberration and positional chromatic aberration; the aberrations related to the field of view are dispersion, field curvature, aberration and magnification packet aberration.
There is a difference between the microscope objective lens and the eyepiece in terms of their involvement in imaging. The objective lens is the most complex and important part of the microscope, working in wide beams (large aperture), but these beams have a small inclination to the optical axis (small field of view); the eyepiece works in narrow beams, but its inclination is large (large field of view). When calculating objective and eyepieces, there is a big difference in the elimination of aberration.
The microscope objective is a spherical aberration cancellation system. This means that for a pair of conjugate points on the axis, when spherical aberration is eliminated and the sinusoidal condition is achieved, there are only two such spherical aberration points per objective. Therefore, any change in the calculated position of the object in relation to the image results in a larger aberration. On the rotator mounted on the lower end of the barrel, there are generally 3-4 objectives, the shortest of which is engraved with the symbol "10×" for low magnification, the longer with the symbol "40×" for high magnification, and the longest with the symbol "100×" for high magnification. "100 ×" symbol for the oil lens, in addition, in the high-magnification lens and oil lens is often added a circle of different colours of the line, to show the difference.
