Optical system for projecting patterns comprising a constant-magnification focusing servocontrol

An optical system for projecting patterns, said system enabling the image of an object having a non-uniform transparency to be reproduced on a photosensitive surface with a predetermined magnification, said system comprising along a same optical axis, a source providing a light beam onto said surface, a lens, a lens holder supporting said lens, a first carriage integral with said lens holder, an object inserted between said source and said lens, an object holder supporting said object, a second carriage integral with said object holder and a support having a photosensitive surface;

• the image of said object being projected onto said support by said lens;
• said system further comprising electromechanical transducer means for moving said lens holder in a direction parallel to said optical axis for the purposes of automatic focusing, first adjusting means for moving said lens holder in said direction enabling the operating range of said transducer means to be centered and second adjusting means for adjusting the distance between said first and second carriages;
• said transducer means and said first adjusting means causing displacements of said first and second carriages simultaneous and of equal amplitude, in order to keep constant said magnification.