Abstract: A projection system includes first and second lens groups respectively having negative and positive power sequentially arranged from the enlargement side toward the reduction side. The first lens group includes a first-a lens group having negative power, a first-b lens group located at the reduction side of the first-a lens group and having negative power, and a first-c lens group located at the reduction side of the first-b lens group and having positive power. The first-b lens group and the first-c lens group each move in the direction of the optical axis during focusing. The projection system satisfies 0.2<|F/F1b|<0.6 (1), 0.0<F/F1c<0.14 (2), BF/F>5.0 (3), where F, F1b, and F1c represent the respective focal lengths of the overall projection system, first-b lens group, and first-c lens group, and BF represents the back focal length in air.

Abstract: An imaging lens includes a first lens having negative refractive power; an aperture stop; a second lens; a third lens; a fourth lens; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side. The fifth lens is formed in a shape so that a surface thereof on the image plane side is concave at a paraxial region thereof. The fifth lens is formed in the shape so that the surface thereof on the image plane side has an aspheric shape having an inflection point. The first lens has a specific Abbe's number ?1. The first lens is disposed away from the second lens by a specific distance. The fifth lens is disposed away from the sixth lens by a specific distance.

Abstract: An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having negative refractive power; a fourth lens having positive refractive power; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens having negative refractive power. The lenses are arranged in this order from an object side to an image plane side. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape having an inflection point.

Abstract: An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens having negative refractive power, arranged in this order from an object side to an image plane side. The imaging lens has a total of nine lenses. The eighth lens has at least one aspheric surface. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The ninth lens is formed in the shape so that the surface thereof on the image plane side has a specific paraxial curvature radius.

Abstract: An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens having negative refractive power, arranged in this order from an object side to an image plane side. The imaging lens has a total of nine lenses. The first lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape.

Abstract: An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens, arranged in this order from an object side to an image plane side. The imaging lens has a total of nine lenses. The first lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape.

Abstract: An optical system includes a first lens having negative refractive power, a stop, a second lens having positive refractive power, an aperture stop, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power, with the lenses sequentially arranged from the magnifying side toward the demagnifying side. The third and fourth lenses are bonded into a doublet, which has negative refractive power. One of the fifth and sixth lenses is made of plastic and has aspherical surfaces on opposite sides, and the other is made of glass. The portion on the demagnifying side of the sixth lens is a telecentric portion. Conditional Expression (1) below is satisfied, SD12/SD2<0.9??(1) where SD12 represents the effective radius of the stop, and SD2 represents the effective radius of the second lens.

Abstract: An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; a fifth lens having positive refractive power; a sixth lens; a seventh lens; an eighth lens; and a ninth lens, arranged in this order from an object side to an image plane side. The imaging lens has a total of nine lenses. The first lens has at least one aspheric surface. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The ninth lens has a specific focal length.

Abstract: A projection system includes a first optical system and a second optical system disposed on an enlargement side of the first optical system. The first optical system includes a first lens group having positive power, a second lens group disposed on the enlargement side of the first lens group and having negative power, and an optical path deflector disposed between the first lens group and the second lens group. The second optical system includes a reflection member having a concave reflection surface. The second lens group includes three aspherical lenses. Conditional Expression (1) below is satisfied, 0.25<|F|×FNO/Ymax<0.5??(1) where F represents the focal length of the entirety of the projection system, FNO represents the F number of the projection system, and Ymax represents a maximum image height in a reduction-side conjugate plane.

Abstract: An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an eighth lens having positive refractive power; and a ninth lens, arranged in this order from an object side an image plane side. The imaging lens has a total of nine lenses. The first lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape.

Abstract: An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an eighth lens having positive refractive power; and a ninth lens, arranged in this order from an object side to an image plane side. The imaging lens has a total of nine lenses. The eighth lens has at least one aspheric surface. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape. The seventh lens has a specific thickness near an optical axis thereof. The eighth lens has a specific thickness near an optical axis thereof.

Abstract: An imaging lens includes a first lens; a second lens having positive refractive power; a third lens; a fourth lens; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side with spaces in between each of the lenses. The second lens is formed in a shape of a meniscus lens near an optical axis thereof. The third lens has at least one aspheric surface. The fourth lens has at least one aspheric surface. The fifth lens is formed in a shape so that a surface thereof on the object side is convex toward the object side near an optical axis thereof. The sixth lens has two aspheric surfaces and the surface on the image plane side is convex toward the image plane side near an optical axis thereof. The second lens has a specific Abbe's number.

Abstract: An imaging lens includes a first lens having positive refractive power; a second lens having positive refractive power; a third lens having negative refractive power; a fourth lens having positive refractive power; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens having negative refractive power, arranged in this order from an object side to an image plane side. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape having an inflection point.

Abstract: An imaging lens includes, in order from an object side to an image side, a first lens L1 having negative refractive power, a second lens L2 having positive refractive power, a third lens L3 having positive refractive power, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 having negative refractive power, wherein said eighth lens L8 has an aspheric image-side surface having at least one inflection point.

Abstract: There is provided a compact imaging lens configured to properly correct aberrations. The imaging lens includes, in order from an object side to an image side, a first lens L1 having negative refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 having negative refractive power. The eighth lens L8 has an aspheric image-side surface having at least one inflection point.

Abstract: An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens having negative refractive power; a fifth lens; a sixth lens; a seventh lens; an eighth lens; and a ninth lens having negative refractive power, arranged in this order from an object side to an image plane side. The ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape having an inflection point.

Abstract: An imaging lens includes a first lens having negative refractive power; a second lens; a third lens; a fourth lens; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side. The first lens is formed in a shape so that a surface thereof on the image side has an aspheric shape. The fourth lens is formed in a shape so that a surface thereof on the image plane side has an aspheric shape. The fifth lens is formed in a shape so that a surface thereof on the image plane side is concave at a paraxial region thereof, and has an aspheric shape having an inflection point. The sixth lens has a specific Abbe's number ?6. The first lens and the fifth lens are disposed away from the second lens and the sixth lens, respectively, by specific distances.

Abstract: There is provided a compact imaging lens configured to properly correct aberrations. The imaging lens includes, in order from an object side to an image side, a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive refractive power, a fourth lens L4 with positive refractive power, a fifth lens L5, a sixth lens L6, a seventh lens L7 with positive refractive power, and an eighth lens L8 with negative refractive power. The eighth lens L8 is formed in a shape of a meniscus lens in a paraxial region, and has an aspheric image-side surface having at least one inflection point. In addition, the following conditional expressions are satisfied: ?5.00<f2/f<?2.00 10.00<f4/f<25.00 where f: a focal length of the overall optical system of the imaging lens, f2: a focal length of the second lens, and f4: a focal length of the fourth lens.

Abstract: A projection optical device includes an incident side optical path on which image light is made incident from a image generation device, a bending member configured to bend the image light having passed through the incident side optical path, an emission side optical path on which the image light bent by the bending member is made incident, the emission side optical path being disposed side by side with the light source device, and a reflection element provided on the emission side optical path and configured to reflect the image light made incident thereon and project the image light to the outside of the exterior housing. The absolute value of f2/f1 satisfies the following expression when a focal length of the projection optical device is represented as f1 and a focal length of the reflection element is represented as f2.

Abstract: An imaging lens includes a first lens having negative refractive power; an aperture stop; a second lens; a third lens; a fourth lens having negative refractive power; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side. The fifth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof. The sixth lens is formed in a meniscus shape at a paraxial region thereof. The first lens and the sixth lens have specific Abbe's numbers.