AUTOMATIC FOCUS ADJUSTING DEVICE

PURPOSE:To execute an automatic focus adjustment even in case of a lens system whose back-focal distance quantity is small by using a part of lenses for constituting a lens system, for a minute quantity variation of an optical path length, and moving it in the optical axis direction by a piezoelectric element. CONSTITUTION:A lens 16 for an optical path length minute variation, which is one piece of lenses for constituting a lens system 6 is incorporated in the lens system through a vibrating device 17 using a piezoelectric element so as to vibrate by a minute distance as shown by arrows (e), (f) in the optical axis direction of the lens system 6. This lens 16 for an optical path length minute variation is fixed to a lens holder 19 by a holding ring 18, the lens holder 19 is fixed by a screw, etc. through a ring 21 to the inside end of a ring plate-shaped piezoelectric element 20, and the outside end is fixed to a lens barrel 23 with a screw through a spacer 22. The lens 16 can be moved minutely in the directions as indicated with arrows (e), (f) by applying a voltage which is varied periodically, to the piezoelectric element 20 through a lead wire by an oscillator.