The invention relates to a lens system.
The German publication 24 36 230 discloses a lens system or objective containing a prism which rotates images. To minimize the size of the objective, the prism is integrated between two groups of lenses. Each group constitutes a converging lens group, and the prism lies on the optical axis. The structure of the German publication requires a real intermediate image, and hence an additional optical arrangement to produce the intermediate image. Accordingly, the cost and length of the objective are relatively great.
Another optical system for effecting image rotation is known from the European patent application 0 157 325. Here, the image is produced by a normal objective. A Porroprism arrangement is used for image rotation, and such arrangement is located outside of the objective, and thus also outside of the focal point. This requires the prisms to be greatly oversized relative to the focal point, particularly for larger projection angles and for the avoidance of vignetting, thereby causing the optical system to be large.