Microscopes of this kind are offered as basic equipment by many microscope manufacturers. An inverted and reversed image is provided in the ocular because of the simple configuration which enables transmission of an image via two fixed deflections by a Bauernfeind prism. In this configuration, the movement of the object and of the ocular intermediate-image are mutually opposing and the users of these apparatus have become accustomed thereto.
For ergonomic reasons, there is a need for the user to have the viewing elevation and viewing angle so as to be changeable. For this purpose, many solutions for microscopes having objectives corrected to form an image in a finite focal plane are known wherein a variation of viewing elevation and viewing angle is provided. These apparatus have a common mirror surface which is also pivoted by about half of the angle when pivoting the binocular viewing unit containing the ocular. In this connection, reference can be made to German published patent application 3,334,690 as well as German Patent 1,098,233, German patent publication 218,692 and German utility model registration 7,931,427. Reference can also be made to U.S. Pat. Nos. 4,798,451; 4,643,541; and 4,576,450. A binocular viewing unit of this kind, which is configured in a simple manner, is disclosed in European published patent application 0,627,642 for a stereomicroscope; however, here too, the objective is without a tube lens and is corrected to form an image in a finite focal plane.
Except for different basic configurations, all these solutions however have at least one of the following disadvantages:
(a) a high number of optical elements and the complexity associated therewith as well as possible image errors and contrast reduction; PA1 (b) an additional intermediate image which is required because of the long optical path whereby the ocular intermediate image is generated so as to be erect and laterally correct in an unaccustomed manner; PA1 (c) high mechanical complexity because several elements on different axes must be moved coupled to each other and at precise angles; PA1 (d) a tube factor of greater than 1 because the path to the intermediate image is too long; and, PA1 (e) the inability to realize an output for a camera in a simple manner.
One problem in this context is that conventional single-lens tube lenses, which are adapted to the microscope, have a focal length in the range of approximately 160 to 200 mm with a body magnification of 1 being pregiven. This relatively high focal length is countered by the requirement that an adapter between the body tube of the microscope and the camera should be realized with the shortest structural length possible.
The focal intercept (approximately 160 mm) of the tube lenses which are conventional for this type of microscope does not permit the image to be transmitted into the intermediate image plane when additional optical planar surfaces such as mirrors or prisms are required for pivoting the binocular viewing unit.