There is provided a lens system composed, in order from an enlargement side, of a first lens group with positive refractive power and a second lens group with positive refractive power, wherein when zooming from a telephoto end to a wide-angle end, a distance between the first lens group and the second lens group decreases and a distance between the second lens group and a conjugate plane on a reduction side increases. The second lens group includes, closest to an enlargement side thereof, a lens with a second end surface that is concave on the enlargement side, and the first lens group includes a lens with an effective diameter of a first end surface closest to the reduction side that is larger than a maximum diameter in the second lens group.

The objective lens has multiple focal lengths within a focal length interval and a relatively small focal-length ratio in a range from 1.05 to 2.75, and a travel-to-focal-length ratio in a range from 0.05 to 0.4. The objective lens has three main lens groups that define a negative-positive-positive optical system configuration. The first lens group has a rearward lens sub-group that is axially movable for focusing so that the lens length stays the same during focusing. The objective lenses use optical compensation rather than mechanical compensation to move between the design focal lengths each having an in-focus image. This simplifies operation while increasing reliability and reducing cost. A small set of one or more of the objective lenses can be used to replace a large set of prime lenses each having a single focal length, so that fewer lenses are needed to cover the same focal length span.

An endoscope includes a plurality of illuminating optical systems, an objective optical system, and an optical-path splitting member. The optical-path splitting member has an optical element which forms a first optical path and a second optical path, and an optical-path length of the first optical path differs from an optical-path length of the second optical path. Illumination light is irradiated to an object from the plurality of illuminating optical systems. The objective optical system has an object-side incidence surface which is located nearest to the object, and each of the plurality of illuminating optical systems has an object-side emergence surface which is located nearest to the object. Each of the object-side emergence surfaces is located on an image side of the object-side incidence surface, and following conditional expression (1) is satisfied:
2.0<Dmin/OPLdiff<50  (1).

A magnification-variable optical system having a small size, a wide angle of view, and high optical performance, an optical apparatus including the magnification-variable optical system, and a method for manufacturing the magnification-variable optical system are provided.

A magnification-variable optical system ZL used for an optical apparatus such as a camera 1 includes a first lens group G1 having a negative refractive power and including at least two lenses, and a rear group GR including at least one lens group disposed on an image side of the first lens group G1, and is configured so that a distance between lens groups adjacent to each other changes at magnification change and a condition expressed by predetermined condition expressions is satisfied.

A magnification-variable optical system having a small size, a wide angle of view, and high optical performance, an optical apparatus including the magnification-variable optical system, and a method for manufacturing the magnification-variable optical system are provided.

A magnification-variable optical system ZL used for an optical apparatus such as a camera 1 includes a first lens group G1 having a negative refractive power, and a rear group GR including at least one lens group disposed on an image side of the first lens group G1, and is configured so that a distance between lens groups adjacent to each other changes at magnification change and a condition expressed by predetermined condition expressions is satisfied.

An image capturing lens system includes three lens groups including five lens elements. The three lens groups are, in order from an object side to an image side: first, second and third lens groups. The five lens elements are, in order from the object side to the image side: first, second, third, fourth and fifth lens elements. The first lens element has an object-side surface being convex in a paraxial region thereof. The second lens element has negative refractive power. At least one lens element has an inflection point. A focal length of the image capturing lens system is varied by changing axial distances between the three lens groups in a zooming process. The image capturing lens system has a long-focal-length end and a short-focal-length end. The second lens group is moved relative to the first lens group along an optical axis in the zooming process.

Wide-angle optical imaging lenses designed to have a wide field of view, stability in optical properties over temperature excursions, and, low chromatic aberrations are described. The lenses are comprised of three lens groups. A first group (counting from the object side) having a negative refractive power comprises two negatively powered elements. The first element has a meniscus shape with a convex object surface. The second lens element has a concave image surface and in preferred embodiments is aspherical. The second group having a positive power comprising two elements. Both elements having positive power. The image surface of the first element in the 2.sup.nd group and the object surface of the 2.sup.nd element in the 2.sup.nd group are both convex. An aperture stop is located between the second and third lens groups. The third lens group has a positive power and includes a cemented doublet or triplet, and a singlet element. Selected lens elements are aspherical and selected lens elements are formed from an optical material having a negative do/dT coefficient.

An objective optical system includes, in order from an object: a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The second lens group includes an aperture stop and moves at a time of changing magnification.

A zoom lens system (10) for imaging, includes, in order from an object side (11); a first lens group (G1) with negative refractive power that moves at the time of zooming; a second lens group (G2) with a positive refractive power that moves at the time of zooming, the second lens group including an aperture stop (St); a third lens group (G3) with a positive refractive power, the position of which is fixed relative to the image plane. The second lens group includes: a first sub-lens group (S1) with a positive refractive power arranged on the object side and having the aperture stop; and a second sub-lens group (S2) with a negative refractive power arranged on the image plane side and configured to move independently of the first sub-lens group at the time of focusing.

Methods and systems are provided for an adaptive illumination system. In one example, an adaptive illumination system comprises an adaptive illuminator comprising at least three optical elements including a first optical element, a second optical element, and a third optical element, wherein a distance between the first optical element and the second optical element is adjustable.