Half tone imaging system

An electrophotographic printing machine for reproducing an original document, including:

• a photoconductive member;
• means for charging at least a portion of said photoconductive member to a substantially uniform level;
• means for exposing the charged portion of said photoconductive member to a light image of the original document recording thereon an electrostatic latent image corresponding thereto;
• a screen comprising a substantially transparent member, and a plurality of grooves formed in said transparent member, the plurality of grooves comprising a first set of grooves and a second set of grooves with the width of each groove of the first set being greater than the width of each groove of the second set and the plurality of grooves being arranged in a repetitive pattern with each groove from the first set being interposed between adjacent grooves of the second set, and
• a light source transmitting light rays through said screen to record a screen pattern on the charged portion of said photoconductive member with the screen pattern and electrostatic latent image being in superimposed registration with one another.