Zoomobjectives for Microscope with short Overall-Length

A most common way for changing magnifications in microscopes is to change objectives by rotating nosepiece or to change tube lenses with different focal lengths, by which vibrations perpendicular to the optical axis could appear, or illuminance on image plane could vary abruptly or the found region of interest on specimen could go lost. Another way is adopting a zoom unit in tube systems, and this increases the microscope's complexity, size and costs as consequence. As an alternative approach we realized a few designs for zoom objective with an overall length around 60mm. All embodiments have two shifting lens groups. Magnifications range from 5x to 20x or from 10x to 40x, and could be changed continuously. At any magnification objectives are corrected to a "diffraction limited" state, i.e. Strehl ratios remain greater than 81%. All designs do not require explicit aperture stops. Ray bundles are only limited by clear diameters of lenses in dependence of magnification. So the numerical aperture changes with the magnification correspondingly. Without using the aperture stop is a significant simplification, that helps reducing manufacturing costs.