Abstract: A wide-angle imaging optical system obtains sufficient information in the image periphery, and achieves high-performance imaging across the entire field of view. The imaging optical system uses stereographic projection, and includes, in sequence from an object, a first lens with a negative refractive power having a convex surface facing the object, a second lens with a negative refractive power, a third lens with a negative refractive power, a fourth lens with a positive refractive power, an aperture stop, a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens with a positive refractive power.

Abstract: A wide-angle imaging optical system obtains sufficient information in the image periphery, and achieves high-performance imaging across the entire field of view. The imaging optical system uses stereographic projection, and includes, in sequence from an object, a first lens with a negative refractive power having a convex surface facing the object, a second lens with a negative refractive power, a third lens with a negative refractive power, a fourth lens with a positive refractive power, an aperture stop, a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens with a positive refractive power.

Abstract: A zoom lens includes in order from an object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, and at the time of zooming, the first lens group is fixed, the second lens group moves, the third lens group moves, and the fourth lens group is fixed. The first lens group includes in order from the object side, a negative lens, a reflecting optical element, and a positive lens. The second lens group includes in order from the object side, an aperture stop, a positive lens, a cemented lens having a negative refractive power, and a positive lens. The cemented lens includes a positive lens and a negative lens.

Abstract: An optical system includes, in order from the object side, an aperture, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power and having a meniscus shape with a convex surface facing the image side, and a fifth lens having a negative refractive power. The optical system satisfies a certain condition.

Abstract: An imaging optical system smaller than conventional systems yet with well-corrected aberrations, comprises five lenses L1-L5 having refractive powers, in order from the object side: positive, negative, positive, positive, and negative, with an aperture at an endmost object-side position. In one embodiment, L1 is biconvex, L2's object-side surface is convex, L5's object-side surface is convex, and 1.0?f3/f1?4.9, f1 and f3 being the focal lengths of L1 and L3, respectively. In a variant thereof, L2 is a meniscus lens and L5's object-side surface is concave. In another embodiment, L1 is glass, and ?4.0<(r6+r7)/(r6?r7)<?0.51, r6 and r7 being paraxial curvature radii of L3's object-and image-side surfaces, respectively. In another embodiment, L1 is glass, and ?1.5<f2 /f<?0.73, f2 being the focal length of L2 and f the focal length of the whole optical system. In yet another embodiment, L1 is glass, and ?11.2<r3/f1<?0.9, r3 being the paraxial curvature radius of L1's image-side surface.

Abstract: An optical system includes, in order from the object side, an aperture, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power and having a meniscus shape with a convex surface facing the image side, and a fifth lens having a negative refractive power. The optical system satisfies a certain condition.

Abstract: An optical system includes, in order from the object side, an aperture, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power and having a meniscus shape with a convex surface facing the image side, and a fifth lens having a negative refractive power. The optical system satisfies a certain condition.

Abstract: A zoom lens includes in order from an object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, and at the time of zooming, the first lens group is fixed, the second lens group moves, the third lens group moves, and the fourth lens group is fixed. The first lens group includes in order from the object side, a negative lens, a reflecting optical element, and a positive lens. The second lens group includes in order from the object side, an aperture stop, a positive lens, a cemented lens having a negative refractive power, and a positive lens. The cemented lens includes a positive lens and a negative lens.

Abstract: An imaging optical system smaller than conventional systems yet with well-corrected aberrations, comprises five lenses L1-L5 having refractive powers, in order from the object side: positive, negative, positive, positive, and, with an aperture at an endmost object-side position. In one embodiment, L1 is biconvex, L2's object-side surface is convex, L5's object-side surface is convex, and 1.0<f3/f1<4.9, f1 and f3 being the focal lengths of L1 and L3, respectively. In a variant thereof, L2 is a meniscus lens and L5's object-side surface is concave. In another embodiment, L1 is glass, and ?4.0<(r6+r7)/(r6?r7)<?0.51, r6 and r7 being paraxial curvature radii of L3's object- and image-side surfaces, respectively. In another embodiment, L1 is glass, and 1.5<f2/f<0.73, f2 being the focal length of L2 and f the focal length of the whole optical system. In yet another embodiment, L1 is glass, and 11.2<r3/f1<0.9, r3 being the paraxial curvature radius of L1's image-side surface.