Automatic focus with variable magnification

A system for automatically focusing images having different magnifications onto a light sensitive medium comprising:

• first means for projecting a light image of a wavelength to which the light sensitive medium is responsive along a first optical path from a projection plane to said light sensitive medium, said first optical path including magnification control means for changing the magnification of said light image by changing the length of said first optical path,
• second means for automatically focusing said image on said light sensitive medium regardless of changes in the magnification of said light image, said second means including
• a. focusing means in addition to said magnification control means situated in said first optical path for changing the length of said first optical path to achieve focus,
• b. means for projecting a first light pattern of a wavelength to which said light sensitive medium is not responsive along a second optical path from a first light pattern producing means to approximately said projection plane and back to said first light pattern producing means,
• c. means for projecting a second light pattern of a wavelength to which said light sensitive medium is not responsive along a third optical path from a second light pattern producing means to approximately said projection plane and back to said second light pattern producing means,
• d. said second and third optical paths each including a substantial part of said first optical path including said magnification control means, and said first and second light pattern producing means each having light transmissive portions, and
• e. servo means coupled to said focusing means and oriented to receive any portions of said first and second light patterns which have followed said second and third optical paths, respectively, and have passed through the light transmissive portions of said first and second light producing means, respectively, for producing movement of said focusing means in a direction to bring said light image into focus on said light sensitive medium.