| 摘要 |
A variable length telescoping viewfinder for cameras that provides a variably adjustable eye viewing distance relative to the camera without changing the focus or magnification of the scene being photographed throughout the telescoping movement of the viewfinder. The light rays of the real image supplied to the viewfinder directly or indirectly from the camera are passed through a field lens, Pechan prism, relay lens system forming collimated light rays from the fixed front module to the movable rear module wherein lens elements form an intermediate image that is viewed through an eyepiece lens group. The front module is weakly powered and of a substantial effective optical length because of the inclusion of the Pechan prism. The image forming lens group of the rear module is weakly powered whereby relative telescopic movement between the front and rear modules does not adversely affect the location, focus or magnification of the intermediate image throughout the range of movement. A magnification lens group is provided for selectively magnifying the intermediate image by moving the magnification lens group into and off the optical axis. The Pechan prism also allows proper orientation of the image. The eyepiece lens group may include a movable lens subgroup for precise focusing.
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