Slope control exposure control apparatus

Claim 1

In document reproducing apparatus including illumination means for projecting light upon a document to expose a medium having a predetermined spectral response to actinic light reflected from such document, actuable means effective when actuated to terminate medium exposure, and non-linear exposure control means including photosensitive means disposed to receive light from the illumination means along, (1) a first path directly from the illumination means, and (2) a second path in which reflected light is received from a portion of such document, said photosensitive means having a parameter the magnitude of which varies as a function of the intensity and spectrum of light received along said first and second paths, the improvement comprising: a. filter means disposed in said first and second paths in optical alignment with said photosensitive means for passing light along said first and second paths to said photosensitive means, said filter means having a predetermined spectral response which modifies the spectrum of the passing light to cause the parameter of said photosensitive means to correlate with the spectral response of such medium; b. a control circuit having charging means coupled to said photosensitive means and responsive to the parameter for producing a charge level which is a function of the magnitude of the parameter; and c. means responsive to a predetermined charge level of said charging means for actuating said actuable means to terminate medium exposure.