Reflectance probe

Claim 1

In a process for monitoring the extent to which a background of fog develops in a non-silver free radical film in which an image is developed by blanket exposure of said film to radiant energy of a suitable wavelength after said film has been subjected to a latent image forming exposure by exposure to a pattern of radiation wherein said film comprises a clear base layer and a photosensitive coating on said base layer, the improvement which comprises: while said image is being developed by said blanket exposure, traversing a non-image area of said film coating with radiation from a light emitting diode, acting as a probe and insufficient to produce any appreciable fogging of said film coating, said radiation being projected to strike said film coating at an angle so that one portion of the probe radiation is reflected from the interface between the film coating and the film base layer and a second portion is reflected from the interface between the film base layer and the surface on which the film base layer is supported; providing radiation sensing means to receive the combination of both of said reflected radiations and to produce a signal indicative of the extent of fogging in said film coating, as a result of said exposure; and causing said blanket exposure for development to be discontinued when the base plus fog reaches the desired level.