Overview of Microscopic Objectives
The objective lens is the most important optical component of a microscope, which uses light to create the first image of the object being tested. Therefore, it directly affects and affects the quality of the image and various optical technical parameters, and is the primary standard for measuring the quality of a microscope.
The structure of objective lenses is complex and precise, usually composed of a combination of lens groups, with each lens separated by a certain distance to reduce the difference. Each group of lenses is made by gluing one or several lenses with different materials and parameters. There are many specific requirements for objective lenses, such as axial alignment and confocal alignment.
Modern microscopic objectives have reached a high level of perfection, with their numerical aperture approaching its limit, and the difference between the resolution of the field center and the theoretical value is negligible. However, there is still a possibility to continue increasing the field of view of the microscope objective and improving the imaging quality of the field edge, and this research work is still ongoing to this day.
Confocal imaging is not only used in microscopic examination, but also when the image is clearly observed using a certain magnification objective lens. When converting to another magnification objective lens, the imaging should also be basically clear, and the center deviation of the image should also be within a certain range, which is the degree of axial alignment. The quality of confocal performance and the degree of alignment are important indicators of microscope quality, which are related to the quality of the objective lens itself and the accuracy of the objective lens converter.
The aberration related to a wide beam of light is spherical aberration, coma aberration, and positional chromatic aberration; The aberrations related to the field of view are astigmatism, field curvature, distortion, and magnification packet aberration.
Microscopic objectives and eyepieces differ in their involvement in imaging. The objective is the most complex and important part of a microscope, operating in a wide beam of light (with a large aperture), but with a smaller inclination angle to the optical axis (with a smaller field of view); The eyepiece operates in a narrow beam of light, but its inclination angle is large (with a large field of view). When calculating the objective and eyepiece, there is a significant difference in eliminating aberration.
A microscopic objective is a system for eliminating spherical aberration. This means that when a pair of conjugate points on the axis eliminate spherical aberration and achieve sinusoidal conditions, each objective has only two such spherical aberration. Therefore, any change in the calculated position of the object and image results in an increase in aberration. On the rotator installed at the bottom of the lens barrel, there are generally 3-4 objective lenses, with the shortest one engraved with "10 ×” The symbol is a low-power mirror, and the longer one is engraved with "40 ×” The symbol is a high-power mirror, and the longest one is engraved with "100 ×” The symbol is oil mirror, and in addition, a circle of different colors is often added on the high-power mirror and oil mirror to indicate the difference.
