Self testing phototypesetter flash intensity control system

A system for establishing proper character illumination intensities in a phototypesetter for various character sizes comprising:

• a. a character projection optical system for imaging a character upon a photosensitive medium;
• b. a character image storage device;
• c. a light source for illuminating selected characters associated with said storage device to produce a character image at the input of said character projection optical system;
• d. a light intensity measuring means for measuring the intensity of light emerging from said character projection optical system;
• e. a reference signal generating means;
• f. a comparator for comparing the signal produced by said reference signal generating means and the signal produced by said light intensity measuring means and for producing an output signal when the signal produced by said light intensity measuring means assumes a given relationship with respect to the value of the signal produced by said reference signal generating means;
• g. a reference image generating means for projecting a reference image through said character projection optical system and at said light intensity measuring means;
• h. first light source intensity control means for causing said light source to sequentially illuminate said reference image generator at varying intensity levels until the signal produced by said light intensity measuring means in turn is in the neighborhood of the signal produced by said reference signal generating means, thereby to cause said comparator to generate said output signal;
• and
• i. a second control means coupled to said comparator, responsive to the generation of said output signal by said comparator for causing said first light source intensity control means to cease changing the intensity of light produced by said light source, thereby to establish the intensity of character images projected upon said photosensitive medium during typesetting of characters which are to have the same size.

A method for establishing proper character illumination intensities in a phototypesetter for various character size images projected through a variable magnification optical system therein comprising:

• a. projecting a first reference light image produced by a light illumination source at a light intensity measuring device through a variable magnification optical system;
• b. measuring the intensity of the light of said reference light image so projected and comparing the measured intensity thereof to a reference signal;
• c. projecting a second reference light image produced by said illumination source at said light intensity measuring means through said optical system having an intensity which differs from the intensity of the first reference image previously projected at said light intensity measuring means and again comparing the measured intensity of said reference image signal with said reference signal;
• d. repeating steps a, b, and c until the measured intensity of the reference image assumes a given relationship with respect to said reference signal and thereafter
• e. maintaining the intensity of light produced by said illumination source constant during further phototypesetting of characters of the same size projected through said optical system.