Afocal zoom for use in microscopes

Abstract

The invention relates to an afocal zoom (1) for use in microscopes of high resolution and high zoom factors having a tube lens (11), the zoom comprising four successive optical assemblies (G1, G2, G3, G4) when viewed from the object end, the first assembly (G1) having a positive focal length (f1), the second assembly (G2) a negative focal length (f2), the third assembly (G3) a positive focal length (f3), and the fourth assembly (G4) a negative focal length (f4), and the first and the fourth assembly (G1, G4) being arranged in stationary fashion and the second and the third assembly (G2, G3) being arranged movably for modifying the magnification of the zoom (1), the zoom magnification decreasing with increasing distance (D23) between the two assemblies (G2, G3). The zoom operates in the range of “useful magnification” of the microscope with sufficient contrast if the zoom meets the following condition (B1) VZO≦41×ENP/fT, where ENP denotes the diameter of the zoom entrance pupil at maximum zoom magnification, and fT the focal length of the tube lens (11) of the microscope, and where ENP>21 mm. It is guaranteed that the zoom operates in the range of useful magnification of the microscope and with a sufficient field-of-view diameter if the condition(B2) is met: tan(w1)≧0.268×z/ENP, where w1 denotes the entrance field angle of the zoom at minimum zoom magnification and z denotes the zoom factor, and where ENP>21 mm and z>15.

Dependencies are inferred from the claim text.