Focal plane detecting device

Abstract

A focal plane detecting device is disclosed which uses an optical fiber system located within a rotating motor shaft or the like to scan an image plane and to deliver the scanned light to a stationary means, such as a photoconductor for developing a contrast signal. The optical system includes at least one optical fiber having its light incident end a fixed distance away from the axis of rotation of the shaft, but facing in the axial direction so as to scan a circular-like pattern of the plane wherein the light incident surface exists. The optical fiber extends through the shaft and exits in such a manner as to direct light therefrom upon a light detector at least part of the time that the shaft is rotating. Preferably the optical system includes a pair of optical fibers each having light incident ends symmetrically about the axis of rotation of the shaft and separated by a distance of .DELTA.Z along the axis of rotation. The axial separation results in the two optical fibers scanning corresponding potions of two image planes separated by .DELTA.Z. This permits the development of image signals representing the slightly separated planes and the comparison of said signals with each other to determine the position of the focal plane relative to the two image planes.