The microscope objective is a spherical aberration elimination system. This means that, with respect to a pair of conjugate points on the axis, when spherical aberration is eliminated and sinusoidal conditions are achieved, each objective has only two such spherical aberration elimination points. Therefore, any change in the calculated position of the object and image will result in an increase in aberration. On the rotator installed at the lower end of the lens barrel, there are usually 3-4 objective lenses, among which the shortest one engraved with the "10 ×" symbol is the low magnification lens, the longer one engraved with the "40 ×" symbol is the high magnification lens, and the longest one engraved with the "100 ×" symbol is the oil lens. In addition, a circle of different colored lines is often added to distinguish between the high magnification lens and the oil lens.