Abstract: A lens unit includes: an imaging optical system; and a lens barrel holding the imaging optical system. The imaging optical system includes, in order from an object side: a first lens having a positive refractive power; a second lens including at least one surface having an aspherical shape; and a third lens having a negative refractive power, at least one surface having an aspherical shape, and an inflection point other than an intersection with an optical axis.

Abstract: An observation optical system of a real-image type includes, in order from the object side, an objective system, a reverse-erecting system that erects an inverted image formed by the objective system, and an eyepiece system that allows a pupil to observe an erect image formed by the reverse-erecting system. The objective system includes, in order from the object side, a first lens having a negative power and a second lens having a positive power. The eyepiece system includes, in the order from the object side, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, and a sixth lens having a positive power.

Abstract: A lens unit includes: an imaging optical system; and a lens barrel holding the imaging optical system. The imaging optical system includes, in order from an object side: a first lens having a positive refractive power; a second lens including at least one surface having an aspherical shape; and a third lens having a negative refractive power, at least one surface having an aspherical shape, and an inflection point other than an intersection with an optical axis.

Abstract: An observation optical system of a real-image type includes, in order from the object side, an objective system, a reverse-erecting system that s erects an inverted image formed by the objective system, and an eyepiece system that allows a pupil to observe an erect image formed by the reverse-erecting system. The objective system includes, in order from the object side, a first lens having a negative power and a second lens having a positive power. The eyepiece system includes, in the order from the object side, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, and a sixth lens having a positive power.

Abstract: A single-focal-length imaging lens system achieves focusing by, while keeping first and third lens groups stationary relative to the image plane, moving a second lens group along the optical axis. The second lens group includes a positive lens element. The third lens group includes an aspherically shaped lens element having an inflection point at a position other than the intersection with the optical axis. The first and second air lenses formed by the intervals between the first and second and between the second and third lens groups have negative and positive refractive powers respectively. The conditional formula 0?|Fi1/Fi2|?|Fm1/Fm2|?10 is fulfilled (Fi1 and Fi2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the infinite object distance; Fm1 and Fm2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the closest object distance).

Abstract: Provided is an imaging lens, and also provided are an image pickup apparatus and a portable terminal both equipped with the imaging lens. The imaging lens includes in order: a positive first lens having a convex object-side surface; a negative second lens having a concave image-side surface; a negative meniscus-shaped third lens having a convex object-side surface; a positive fourth lens having a convex image-side surface; and a negative fifth lens having a concave image-side surface. The image-side surface of the fifth lens is aspherical and has an inflection point at a position of the optical axis. The third and the fourth lenses are integrally moved to focus, and the following conditional relation is satisfied: 0.75<f34/f<1.30, where f34 is the combined focal length of the third lens and the fourth lens, and f is the focal length of the entire system of the imaging lens.

Abstract: The imaging optical system has a first positive lens element convex toward the object side, a second negative lens element concave toward the image side, a third lens element having both surfaces with a region, in which the lens section is located on the object side than the intersection with the optical axis, a fourth positive lens element convex toward the image side with at least one surface having an aspherical shape and inflection points, and a fifth negative lens element concave toward the image side. The optical system satisfies the expressions: 0.5<|f1/f|<0.67, 0.3<|f4/f|<0.63 The third lens element satisfies the expressions: ?0.4<f/R1—L3<0.2, ?0.6<f/R2—L3<0.05 where f, f1, f4 denote focal lengths of the entire system, the first lens element, and the fourth lens element, and R1_L3, R2_L3 denote paraxial diameters of the object-side surface and the image-side surface of the third lens element.

Abstract: A single-focal-length imaging lens system achieves focusing by, while keeping first and third lens groups stationary relative to the image plane, moving a second lens group along the optical axis. The second lens group includes a positive lens element. The third lens group includes an aspherically shaped lens element having an inflection point at a position other than the intersection with the optical axis. The first and second air lenses formed by the intervals between the first and second and between the second and third lens groups have negative and positive refractive powers respectively. The conditional formula 0?|Fi1/Fi2|?|Fm1/Fm2|?10 is fulfilled (Fi1 and Fi2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the infinite object distance; Fm1 and Fm2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the closest object distance).

Abstract: Provided is an imaging lens, and also provided are an image pickup apparatus and a portable terminal both equipped with the imaging lens. The imaging lens includes in order: a positive first lens having a convex object-side surface; a negative second lens having a concave image-side surface; a negative meniscus-shaped third lens having a convex object-side surface; a positive fourth lens having a convex image-side surface; and a negative fifth lens having a concave image-side surface. The image-side surface of the fifth lens is aspherical and has an inflection point at a position of the optical axis. The third and the fourth lenses are integrally moved to focus, and the following conditional relation is satisfied: 0.75<f34/f<1.30, where f34 is the combined focal length of the third lens and the fourth lens, and f is the focal length of the entire system of the imaging lens.