Abstract: The diffractive optical element includes two diffraction gratings made of different materials and being in contact with each other at their grating surfaces. The materials satisfy the following conditions, and the second material is obtained by mixing a resin material with a particulate material satisfying the following conditions: nd1?1.48, ?d1?40, (?1.665E?07×?d13+5.213E?05×?d12?5.656E×03×?d1+0.675)??g,F1?(?1.665E?07×?d13+5.213E?05×?d12?5.656E?03×?d1+0.825), (?1.687E?07×?d13+5.702E?05×?d12?6.603E?03×?d1+1.400)??g,d 1?(?1.687E?07×?d13+5.702E?05×?d12?6.603E?03×?d1+1.580), nd2?1.6, ?d2?30, ?g,F2?(?1.665E?07×?d23+5.213E?05×?d22?5.656E?03×?d2+0.675 ), ?g,d2?(?1.687E?07×?d23+5.702E?05×?d22?6.603E?03×?d2+1.400 ), nd1-nd2?0, ndb2?1.70, ?db2?20. The element achieves a high diffraction efficiency in a specific diffraction order over a wide wavelength range.

Abstract: An image-pickup optical system includes, from the object side to the image side, a first lens unit having positive optical power, an aperture stop, and a second lens unit. A diffractive optical element and a lens composed of extraordinary partial dispersion material are appropriately disposed in the optical system. The image-pickup optical system is capable of reducing the generation of flare and ghosts at the diffractive optical element and effectively correcting chromatic aberration.

Abstract: A zoom lens system includes a frontmost first lens unit having a negative optical power and a plurality of lens units on the rear side thereof. The first lens unit consists of a negative lens element. The zoom lens system includes five or less lens elements in total. The Abbe number of the negative lens element and the exit pupil distance of the zoom lens system at a wide-angle end are appropriately adjusted.

Abstract: An image-pickup optical system includes, from the object side to the image side, a first lens unit having positive optical power, an aperture stop, and a second lens unit. A diffractive optical element and a lens composed of extraordinary partial dispersion material are appropriately disposed in the optical system. The image-pickup optical system is capable of reducing the generation of flare and ghosts at the diffractive optical element and effectively correcting chromatic aberration.

Abstract: Among a plurality of lens units constituting an optical system, at least one of the plurality of lens units includes a refractive optical element made of a solid material that satisfies the following conditions: 3<?d<30 0.10<?gd<1.25 0.10<?gF<0.60 where ?d is an Abbe number of the solid material and ?gd and ?gF represent partial dispersion ratios of the solid material. The refractive optical element made of the solid material has refractive power with a sign opposite to a sign of refractive power of the lens unit including the refractive optical element.

Abstract: A zoom lens system includes a frontmost first lens unit having a negative optical power and a plurality of lens units on the rear side thereof. The first lens unit consists of a negative lens element. The zoom lens system includes five or less lens elements in total. The Abbe number of the negative lens element and the exit pupil distance of the zoom lens system at a wide-angle end are appropriately adjusted.

Abstract: Among a plurality of lens units constituting an optical system, at least one of the plurality of lens units includes a refractive optical element made of a solid material that satisfies the following conditions: 3<vd<30 0.10<?gd<1.25 0.10<?gF<0.60 where ?d is an Abbe number of the solid material and ?gd and ?gF represent partial dispersion ratios of the solid material. The refractive optical element made of the solid material has refractive power with a sign opposite to a sign of refractive power of the lens unit including the refractive optical element.

Abstract: There are provided a zoom lens system comprising, 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, and at least one diffraction optical element.

Abstract: A zoom lens system which allows a reduction in size. This zoom lens makes two points at different distances have an optically conjugate relationship, and sequentially includes, from a first conjugate point side at a longer distance to a second conjugate point side at a shorter distance, a first lens unit having a negative optical power, a second lens unit, a third lens unit, a fourth lens unit, a fifth lens unit, and a sixth lens unit. A plurality of lens units of the first to sixth lens units move for zooming, and at least one lens unit of the first to sixth lens units has a diffractive optical element.

Abstract: A zoom lens system which allows a reduction in size. This zoom lens makes two points at different distances have an optically conjugate relationship, and sequentially includes, from a first conjugate point side at a longer distance to a second conjugate point side at a shorter distance, a first lens unit having a negative optical power, a second lens unit, a third lens unit, a fourth lens unit, a fifth lens unit, and a sixth lens unit. A plurality of lens units of the first to sixth lens units move for zooming, and at least one lens unit of the first to sixth lens units has a diffractive optical element.

Abstract: There are provided a zoom lens system comprising, 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, and at least one diffraction optical element.