In high-quality microscopy, it is of great significance that the object information is transmitted to the image plane free of so-called image errors (aberrations). If deviations from the calculated ideal conditions occur, aberrations are generated. One form of such aberrations are, e.g., necessary system tolerances, which are unavoidable for the manufacture of a cost-efficient microscope. The aberrations generated by the tolerances are, as a rule, eliminated with suitable adjustment options. However, during the everyday use of the microscope, there are also influences on the ideal conditions that cannot be changed with adjustments and lead to aberrations, which visibly degrade the optical image. Examples of such aberrations are thermal influences or tolerance deviations of the cover glasses to be used. For example, a deviation of the cover glass thickness by merely 0.01 mm can lead to a significant spherical aberration in high-aperture microscope objectives.
For applications in “live cell” microscopy, it is advantageous to operate with temperatures of up to 37 degrees Celsius. Once again, spherical aberrations occur. In order to create good working conditions for these applications as well, microscope objectives with a corrective function for eliminating the spherical aberration have been developed. This corrective function is realized using adjustable air gaps or air gap combinations between the optical elements of the microscope objective. E.g., such a solution is introduced in U.S. Pat. No. 5,940,220. Here, the distance changes are only allowed to influence the image error, which is generated by the type of application and supposed to be eliminated. This requires that such distance effects be specifically produced during the development phase of the optical system.
In modern microscopy, focusing into the sample is the increasingly preferred method. This changes the immersion condition, for which a special objective has been developed. Due to the spectral changes of the refractive index between the immersion and the sample, significant longitudinal chromatic aberrations, in addition to spherical aberrations, can occur even in the axis region which destroy the achromatic and apochromatic properties of a microscope objective, and therefore considerably degrade the chromatic image.
The same condition occurs when objectives with different immersions are used. Once the dispersive properties of the immersions deviate from one another, an additional longitudinal chromatic aberration is generated and the achromatic and apochromatic properties of a microscope objective are therefore also lost.