The objective lens is the most important optical component of the microscope. It uses light to image the inspected object for the first time. Therefore, it is directly related to and affects the quality of imaging and various optical technical parameters. It is the primary standard for measuring the quality of a microscope.
The structure of the objective lens is complex and the production is precise, and it is usually composed of lens groups, and the lenses are separated by a certain distance from each other to reduce the aberration. Each group of lenses is made of one or several lenses of different materials and parameters cemented together. Objectives have many specific requirements, such as co-axial, parfocal.
Modern microscope objectives have reached a high degree of perfection, and their numerical apertures are close to the limit, and the difference between the resolution at the center of the field of view and the theoretical value is very small. However, the possibility of continuing to increase the field of view of the microscope objective and to improve the imaging quality at the edge of the field of view still exists, and this research work is still in progress.
Parfocal is not only in the microscope inspection, when the image is clear with an objective lens of a certain magnification, when the objective lens of another magnification is converted, the imaging should be basically clear, and the center deviation of the image should also be within a certain range. , that is, the degree of co-axiality. The quality of the parfocal performance and the degree of co-axiality are an important indicator of the quality of the microscope, which is related to the quality of the objective lens itself and the accuracy of the objective lens converter.
Aberrations related to broad beams are spherical aberration, coma, and positional chromatic aberration; field-related aberrations are astigmatism, field curvature, distortion, and magnification packet aberration.
Microscope objectives differ from eyepieces in that they participate in imaging. Objectives are the most complex and important part of the microscope, working in wide beams (large aperture), but these beams are less inclined to the optical axis (viewing angle). Small field); the eyepiece works in a narrow beam, but its inclination angle is large (large field of view). When calculating the objective lens and the eyepiece, there is a big difference in eliminating aberrations.
The microscope objective is an aspheric system. This means that, with respect to a pair of conjugate points on the axis, when spherical aberration is eliminated and the sinusoidal condition is achieved, there are only two such aspheric points per objective. Therefore, any change in the calculated position of the object and the image results in a larger aberration. Installed on the rotator at the lower end of the lens barrel, there are generally 3-4 objective lenses, of which the shortest one with a "10×" symbol is a low-power mirror, the longer one with a "40×" symbol is a high-power mirror, and the most The long one engraved with the "100×" symbol is the oil mirror. In addition, a circle of different colors is often added to the high power mirror and the oil mirror to show the difference.
