Zoom lens system, image projecting and image pick-up devices using the same

A zoom lens system comprising, in order from a more distant conjugate point for said zoom lens system, a first lens unit of negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth, and fifth lens units, wherein the nearest lens unit in said zoom lens system to more distant conjugate point is said first lens unit and separation between each lens unit varies during zooming, and said zoom lens system further comprises at least one diffraction optical element,

• wherein said diffraction optical element is formed by combining two diffraction gratings having the same grating thickness and facing each other so as to make a flat a surface of said diffraction optical element.

A zoom lens system comprising, in order from a more distant conjugate point for said zoom lens system, a first lens unit of negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth and fifth lens units, wherein the nearest lens unit in said zoom lens system to more distant conjugate point is said first lens unit and separation between each lens unit varies during zooming, and said zoom lens system further comprises at least one diffraction optical element,

• wherein said diffraction optical element is formed by combining a plurality of diffraction gratings with each other.

A zoom lens system comprising, in order from a more distant conjugate point for said zoom lens system, a first lens unit of negative refractive power, a second lens unit of refractive power which moves during zooming, third, fourth and fifth lens units, wherein the nearest lens unit in said zoom lens system to more distant conjugate point is said first lens unit and separation between each lens unit varies during zooming, and said zoom lens system further comprises at least one diffraction optical element,

• wherein said diffraction optical element is formed by combining a plurality of diffraction gratings facing each other via air.

An image-projecting device comprising a zoom lens system that comprises, in order from a more distant conjugate point, a first lens unit of negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth and fifth lens units, wherein the nearest lens unit in said zoom lens system to more distant conjugate point is said first lens unit, and separation between each lens unit varies during zooming, and said zoom lens system further comprises at least one diffraction optical element, wherein said image-projecting device projects an original image to a subject surface located at a less distant conjugate position for said zoom lens system,

• wherein said diffraction optical element is made of stacked layers of diffraction gratings.

An image pick-up device comprising a zoom lens system that comprises, in order from a more distant conjugate point, a first lens unit of a negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth and fifth lens units, wherein said zoom lens system further comprises at least one diffraction optical element, wherein said image pick-up device uses said zoom lens system to project an image of an object onto a photosensitive body located at a less distant conjugate position for said zoom lens system,

• wherein said diffraction optical element is made of stacked layers of diffraction gratings.