Method of automatically focusing glass-mounted and glassless slides in slide projectors

Claim 1

A method of automatically focusing glass-mounted and glassless slides in slide projectors in which a mask aperture arranged sideways to the optical axis of a projection system is illuminated by an IR light source, imaged onto a glass-mounted or glassless slide via a first optical system and reflected from said glassless or glass-mounted slide so as to be projected in a considerably reduced size onto a receptor via a second optical system positioned on the other side of said optical axis, wherein a projected image provides a signal for controlling a focusing device for focusing said glassless or glass-mounted slide relative to said projection system, and in which multiple reflected aperture images are projected for a glass-mounted slide, the method comprising the steps of: i) focusing said multiple aperture images reflected from said glass-mounted slide onto a CDD line sensor; ii) detecting the number and spacing of said multiple images with respect to their sequence on said CDD line sensor via electronic means; iii) projecting the second of said multiple reflected aperture images onto a predetermined cell of said CDD line sensor by shifting an autofocusing device and projection lens carrier of said projection system via electromechanical adjusting means; and iv) simultaneously with iii) producing a signal corresponding to the spacing between the first and second of said reflected apertures causing said autofocusing device to adjust said projection lens carrier by said spacing.

Claim 2

A method of automatically focusing glass-mounted and glassless slides in slide projectors in which a mask aperture arranged sideways to the optical axis of a projection system is illuminated by an IR light source, imaged onto a glass-mounted or glassless slide via a first optical system and reflected from said glassless or glass-mounted slide so as to be projected in a considerably reduced size onto a receptor via a second optical system positioned on the other side of said optical axis, wherein a projected image provides a signal for controlling a focusing device for focusing said glassless or glass-mounted slide relative to said projection system, and in which multiple reflected aperture images are projected for a glass-mounted slide, the method comprising the steps of: i) focusing said multiple aperture images reflected from said glass-mounted slide onto a CDD line sensor; ii) detecting the number and spacing of said multiple images with respect to their sequence on said CDD line sensor via electronic means; iii) projecting the second of said multiple reflected aperture images onto a predetermined cell of said CDD line sensor by shifting an autofocusing device and projection lens carrier of said projection system via electromechanical adjusting means; and iv) simultaneously with iii) producing a signal corresponding to the spacing between the first and second of said reflected apertures causing said autofocusing device to adjust said projection lens carrier by said spacing.