The known stereoscopic arrangements are based on two separate microscopic beam paths for respective eyes of the viewer. The conventional arrangements are the Greenough type and the Galilei type. Both types have the disadvantage which is the limitation of microscopic resolution so that apertures greater than 0.1 are possible only with substantial complexity. This comes about because large working distances are desired in stereo arrangements and since, for conventional arrangements, only limited aperture space is present because of the following: the required angle for the stereo viewing, the two separate beam paths and the frame parts of the two beam paths with manipulable dimensioning.
It is further known to insert half diaphragms in the form of polarization filters in the condenser of a single-objective microscope in order to obtain a stereoscopic effect. The polarization directions of the polarization filters are mutually perpendicular and correspondingly orientated polarization filters must be provided in the two tubes. In this connection, reference can be made to the “Journal of Microscopy”, volume 153, February 1989, pages 181 to 186.
Published German patent application 4,311,603 discloses a stereomicroscope having a high magnification wherein an object translator is provided in the beam path on the object side of a single-objective light microscope in the object plane. A beam switchover device is mounted in the beam path on the image side. Disadvantageous is here the object translator because the movement of the translator can lead to vibrations of the entire microscope, especially for objects having a large mass.
U.S. Pat. Nos. 4,561,731 and 4,806,776 disclose that a pseudo stereoscopic effect can be generated with the aid of a so-called differential polarization illumination. For the illumination, two separate light sources are provided and polarizers are mounted downstream thereof for generating different polarization directions.
U.S. Pat. No. 4,561,731 shows in FIG. 10 thereof and in the description corresponding thereto that a proper stereoscopic image can be generated in that polarizers are mounted in the light path of the oculars and a double refracting plate is mounted between objective and object. The single illuminating beam path is alternately polarized differently.
A similar arrangement is described in PCT patent publication WO 94/02872. Here too, two light sources and two beam paths are utilized.
This also applies to a surgical microscope disclosed in published German patent application DD-A5 290,278. Two illuminating systems lying diametrically opposite to each other are inclined to the optical axis and the image viewed in the right ocular is assigned to the first illuminating system and the image viewed with the left ocular is assigned to the second illuminating system.
A method for generating stereoscopic images of an object is described in U.S. Pat. No. 5,835,264, incorporated herein by reference. This method includes the steps of illuminating an object with an illuminating beam; masking the illuminating beam to generate a first component beam to illuminate the object at a first angle and provide a first image of the object to a first viewing eye; again masking the illuminating beam to generate a second component beam to illuminate the object at a second angle and to provide a second image of the object to a second viewing eye; and, alternately repeating the last two steps at a frequency above the flicker frequency of the human eye.
The arrangement for carrying out the above method includes a beam generating device for alternately generating first and second illuminating beam components which illuminate the object via illuminating optics at respectively different angles to produce respective images of the object. A directing device alternately directs the images to the left and right eyes of a viewer at a frequency above the flicker frequency of the human eye.
Stereoscopic viewing has as a condition precedent that the viewing is through both eyes. It is based on the fact that, because of the spacing of the eyes, the viewing direction toward an object is different for each eye and therefore the two retinal images are not identical. It is only in the brain that the two images are processed to a single total impression which leads to a spatial display.
In conventional one-objective microscopes, one views also only one plane when using a binocular tube, namely, the focal plane, that is, a narrow range of depth which corresponds to the depth of field. The objects, which are visible simultaneously within this region, appear all to be projected into the same plane because both eyes see the same image.
In order to arrive at a spatial image in microscopy, each eye must be offered a different microscopic image. The above can be two microscopic images which either are viewed for each eye at a different angle or are illuminated for each eye at a different angle. This stereo angle lies essentially in the region from approximately ±7° to ±15°.
An example for the utilization of the stereo observation at two different illuminating angles is a modification of the half-diaphragm method of Ernst Abbe as set forth in the text of H. Beyer entitled “Handbuch der Mikroskopie”, second edition, VEB Verlag der Technik, Berlin, 1977, page 345, which is incorporated herein by reference.
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