Abstract: An ocular optical system including a Fresnel lens having a plurality of Fresnel zones formed on a lens surface on an observation object side, the plurality of Fresnel zones being arranged concentrically side by side along an aspherical surface having a shape which is rotationally symmetric with respect to a central axis of the Fresnel lens, the ocular optical system satisfying the conditional expression 0<PAE1/PAC1?0.50, where PAE1 represents an average pitch in a radial direction of Fresnel zones formed in a portion having a radius of 15 mm or more from the central axis of the Fresnel lens, and PAC1 represents an average pitch in the radial direction of Fresnel zones formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens excluding a first Fresnel zone.

Abstract: An ocular optical system (EL) comprises a Fresnel lens (L1) including a plurality of Fresnel zones (FR) formed on a lens surface on an observation object side. The plurality of Fresnel zones (FR) are arranged concentrically side by side along an aspherical surface having a shape which is rotationally symmetric with respect to a central axis of the Fresnel lens (L1). The ocular optical system satisfies the following conditional expression. 0<PAE1/PAC1?0.50, where PAE1 represents an average pitch in a radial direction of Fresnel zones (FR) formed in a portion having a radius of 15 mm or more from the central axis of the Fresnel lens (L1), and PAC1 represents an average pitch in the radial direction of Fresnel zones (FR) formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens (L1) excluding a first Fresnel zone (FR)(1).

Abstract: An ocular optical system (EL) comprises, in order from an eye point (EP), a first lens group (G1) having a positive refractive power and a second lens group (G2) having a positive refractive power. The second lens group (G2) includes a cemented lens having two optical members cemented together. A cemented surface of the cemented lens is a diffraction optical surface configuring a diffraction grating. A lens surface on one side in a lens constituting the first lens group (G1) is a first Fresnel surface (FSa), and a lens surface on one side in the cemented lens of the second lens group (G2) is a second Fresnel surface (FSb).

Abstract: An imaging lens (PL) has an image surface (I) curved to have a concave surface facing an object and comprises, in order from the object along the optical axis (Ax): a first lens (L1) having positive refractive power; a second lens (L2) having negative refractive power; a third lens (L3) having positive refractive power; a fourth lens (L4) having positive or negative refractive power; and a fifth lens (L5) having at least one lens surface formed as an aspherical surface and having negative refractive power. The following conditional expression is satisfied: 0.005<f/|f4|<0.5 where, f denotes a focal length of the imaging lens (PL), and f4 denotes a focal length of the fourth lens (L4).

Abstract: An ocular optical system (EL) comprises, in order from an eye point (EP), a first lens group (G1) having a positive refractive power and a second lens group (G2) having a positive refractive power. The second lens group (G2) includes a cemented lens having two optical members cemented together. A cemented surface of the cemented lens is a diffraction optical surface configuring a diffraction grating. A lens surface on one side in a lens constituting the first lens group (G1) is a first Fresnel surface (FSa), and a lens surface on one side in the cemented lens of the second lens group (G2) is a second Fresnel surface (FSb).

Abstract: An objective lens (OL) according to the present invention comprises, in order from an object side, a first lens group (G1) having positive refractive power, and a second lens group (G2) having negative refractive power. The first lens group (G1) comprises a positive meniscus lens (L1) having a concave surface facing the object side, a positive lens (L2) dispose close to an image of the positive meniscus lens (L1), and a diffractive optical element (DOE) having a diffractive optical surface (D). The second lens group (G2) is composed of three cemented lenses (CL21 to CL23) which are configured with a positive lens and a negative lens cemented each other. When d00 denotes a distance from the object side to the positive meniscus lens (L1), and TL0 denotes a distance from the object side to the objective lens rear end surface, 0.11?d00/TL0?0.19 is satisfied.

Abstract: An imaging lens (PL) has an image surface (I) curved to have a concave surface facing an object and comprises, in order from the object along the optical axis (Ax): a first lens (L1) having positive refractive power; a second lens (L2) having negative refractive power; a third lens (L3) having positive refractive power; a fourth lens (L4) having positive or negative refractive power; and a fifth lens (L5) having at least one lens surface formed as an aspherical surface and having negative refractive power. The following conditional expression is satisfied: 0.005<f/|f4|<0.5 where, f denotes a focal length of the imaging lens (PL), and f4 denotes a focal length of the fourth lens (L4).

Abstract: A zoom optical system has, in order from an object: a first lens group G1 having positive refractive power; a second lens group G2 having negative refractive power; a third lens group G3 having positive refractive power; and a fourth lens group G4 having negative refractive power, wherein the mutual distance between the lens groups G1 to G4 change upon zooming, and one of the third lens group G3 and the fourth lens group G4 includes at least one diffractive optical element PF.

Abstract: Provided is a zoom optical system which includes, in order from an object, a first lens group having negative refractive power and other lens groups, and in which an interval between each lens group changes upon zooming, wherein the first lens group includes a first negative lens which is disposed closest to the object and has a diffractive optical element on an image side lens surface, and a positive lens disposed closer to the image than the first negative lens, and the glass material used for the positive lens satisfies the following conditions expressions: ?1p?35 and ?(?g, F)?0.

Abstract: An objective lens (OL) according to the present invention comprises, in order from an object side, a first lens group (G1) having positive refractive power, and a second lens group (G2) having negative refractive power. The first lens group (G1) comprises a positive meniscus lens (L1) having a concave surface facing the object side, a positive lens (L2) dispose close to an image of the positive meniscus lens (L1), and a diffractive optical element (DOE) having a diffractive optical surface (D). The second lens group (G2) is composed of three cemented lenses (CL21 to CL23) which are configured with a positive lens and a negative lens cemented each other. When d00 denotes a distance from the object side to the positive meniscus lens (L1), and TL0 denotes a distance from the object side to the objective lens rear end surface, 0.11?d00/TL0?0.19 is satisfied.

Abstract: A catadioptric imaging lens includes: a first reflecting mirror; a second reflecting mirror; and a lens group. A reflecting surface of the first reflecting mirror is a rotationally asymmetrical aspherical, with concavity on the object side within the reference and the first orthogonal plane. A reflecting surface of the second reflecting mirror is a rotationally asymmetrical aspherical, with convexity toward the first reflecting mirror within the reference and within the second orthogonal plane. A surface in the lens group closest to the second reflecting mirror is a rotationally asymmetrical aspherical, with concavity toward the second reflecting mirror within the reference plane and convexity toward the second reflecting mirror within the third orthogonal plane.

Abstract: A telescope optical system having an objective lens system and an eyepiece lens system; wherein: the objective lens system includes a multi-layer-type diffractive optical element (PFo), and cemented lenses (So1) provided with a lens having positive refractive power and a lens having negative refractive power; the eyepiece lens system includes a multi-layer-type diffractive optical element (PFe), and cemented lenses (Se1) provided with a lens having negative refractive power and a lens having positive refractive power; and the condition represented by: 2?|(Po/FNO)/{Pe/(?×m)}|?15 is satisfied, where Ko represents the power of the objective lens system, Kodoe represents the power of the diffractive optical element (PFo) of the objective lens system, and Po is defined as Po=Kodoe/Ko; Ke represents the power of the eyepiece lens system, Kedoe represents the power of the diffractive optical element (PFe) of the eyepiece lens system, and Pe is defined as Pe=Kedoe/Ke; and FNO represents the F-number of the objective

Abstract: Provided is a zoom optical system which includes, in order from an object, a first lens group having negative refractive power and other lens groups, and in which an interval between each lens group changes upon zooming, wherein the first lens group includes a first negative lens which is disposed closest to the object and has a diffractive optical element on an image side lens surface, and a positive lens disposed closer to the image than the first negative lens, and the glass material used for the positive lens satisfies the following conditions expressions: ?1p?35 and ?(?g, F)?0.

Abstract: An achromatic lens system is provided with a cemented resin lens having positive refractive power constructed by a resin lens L11 having positive refractive power cemented with a resin lens L12 having negative refractive power, and a close-contact multi-layer type diffractive optical element L11E, the diffractive optical element L11E being disposed to an image side of the cemented resin lens, the diffractive optical element L11E being constructed by cementing two diffractive element members DE11, DE12 each made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface Gf on which grooves of a diffraction grating are formed, there by being lightweight and easily manufactured, capable of excellently correcting chromatic aberration and spherical aberration at the same time.

Abstract: A catadioptric imaging lens includes: a first reflecting mirror; a second reflecting mirror; and a lens group. A reflecting surface of the first reflecting mirror is a rotationally asymmetrical aspherical, with concavity on the object side within the reference and the first orthogonal plane. A reflecting surface of the second reflecting mirror is a rotationally asymmetrical aspherical, with convexity toward the first reflecting mirror within the reference and within the second orthogonal plane. A surface in the lens group closest to the second reflecting mirror is a rotationally asymmetrical aspherical, with concavity toward the second reflecting mirror within the reference plane and convexity toward the second reflecting mirror within the third orthogonal plane.

Abstract: A zoom optical system has, in order from an object: a first lens group G1 having positive refractive power; a second lens group G2 having negative refractive power; a third lens group G3 having positive refractive power; and a fourth lens group G4 having negative refractive power, wherein the mutual distance between the lens groups G1 to G4 change upon zooming, and one of the third lens group G3 and the fourth lens group G4 includes at least one diffractive optical element PF.

Abstract: A telescope optical system having an objective lens system and an eyepiece lens system; wherein: the objective lens system includes a multi-layer-type diffractive optical element (PFo), and cemented lenses (So1) provided with a lens having positive refractive power and a lens having negative refractive power; the eyepiece lens system includes a multi-layer-type diffractive optical element (PFe), and cemented lenses (Se1) provided with a lens having negative refractive power and a lens having positive refractive power; and the condition represented by: 2?|(Po/FNO)/{Pe/(?×m)}|?15 is satisfied, where Ko represents the power of the objective lens system, Kodoe represents the power of the diffractive optical element (PFo) of the objective lens system, and Po is defined as Po=Kodoe/Ko; Ke represents the power of the eyepiece lens system, Kedoe represents the power of the diffractive optical element (PFe) of the eyepiece lens system, and Pe is defined as Pe=Kedoe/Ke; and FNO represents the F-number of the objective

Abstract: An achromatic lens system is provided with a cemented resin lens having positive refractive power constructed by a resin lens L11 having positive refractive power cemented with a resin lens L12 having negative refractive power, and a close-contact multi-layer type diffractive optical element L11E, the diffractive optical element L11E being disposed to an image side of the cemented resin lens, the diffractive optical element L11E being constructed by cementing two diffractive element members DE11, DE12 each made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface Gf on which grooves of a diffraction grating are formed, there by being lightweight and easily manufactured, capable of excellently correcting chromatic aberration and spherical aberration at the same time.

Abstract: An achromatic lens system is provided with a cemented resin lens having positive refractive power constructed by a resin lens L11 having positive refractive power cemented with a resin lens L12 having negative refractive power, and a close-contact multi-layer type diffractive optical element L11E, the diffractive optical element L11E being disposed to an image side of the cemented resin lens, the diffractive optical element L11E being constructed by cementing two diffractive element members DE11, DE12 each made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface Gf on which grooves of a diffraction grating are formed, there by being lightweight and easily manufactured, capable of excellently correcting chromatic aberration and spherical aberration at the same time.

Abstract: An eyepiece system has a lens group S1 in which a lens L1 having a negative refractive index and refractive power and a lens L2 having a positive refractive index and refractive power are joined, so that the lens group S1 as a whole has a positive refractive index and refractive power; and a multi-layer (stacked) diffraction optical element PF. In an optical system positioned between an image surface I and an eye point EP, the position of a diffraction plane on the optical axis is between EF in FIG. 1. In FIG. 1, EF is the range in which the value ra of the ratio between a distance (DH2) between the diffraction plane (C) and a principal point (H2) near the diffraction plane and a distance (DH1H2) between principal points is 0.5 or less in both directions from the principal points H1, H2.