Abstract: A focusing group G1 is disposed on an object side relative to a variator group G2. The focusing group G1 includes, in order from the object side, a first group G11 having a positive refractive power, a second group G12 having a positive refractive power, and a third group G13 having a positive refractive power. The first group G11 has, in order from the object side, at least one concave lens (L11) and at least one convex lens. When focusing from an infinitely distant object to a close object, the second group G12 and the third group G13 are moved so that with respect to a change in an object distance, an amount of movement of the second group G12 becomes large in a region near infinity, while an amount of movement of the third group G13 becomes large in a close range.

Abstract: A zoom lens comprises: a stationary group that is stationary at the time of variable power; and a variable power group, disposed on an image side of the stationary group, that makes a variable power operation by moving in an optical axis direction at the time of variable power, wherein the stationary group comprises: a first lens group including a negative meniscus lens and a positive lens and having a positive refractive power as a whole; and a second lens group, disposed on the image side of the first lens group, including: a negative lens group including a negative meniscus lens and a positive lens; and a positive lens group including at least one positive lens, in order from an object side, the second lens group having a positive refractive power as a whole.

Abstract: A focusing group G1 is disposed on an object side relative to a variator group G2. The focusing group G1 includes, in order from the object side, a first group G11 having a positive refractive power, a second group G12 having a positive refractive power, and a third group G13 having a positive refractive power. The first group G11 has, in order from the object side, at least one concave lens (L11) and at least one convex lens. When focusing from an infinitely distant object to a close object, the second group G12 and the third group G13 are moved so that with respect to a change in an object distance, an amount of movement of the second group G12 becomes large in a region near infinity, while an amount of movement of the third group G13 becomes large in a close range.

Abstract: An extender optical system, for insertion between a photographic main lens and a camera body for changing the focal length of the lens system as a whole to the long focus side, is formed of, in order from the object side, a first lens group having negative refractive power, a second lens group formed of a single negative lens, and a third lens group having positive refractive power. The negative lens that constitutes the second lens group is made to move in directions that are normal to the optical axis so as to correct for what would otherwise be blurred images due to vibrations. Various conditions are preferably satisfied so as to ensure high image quality over the entire field of view.

Abstract: A retrofocus wide-angle lens is formed of only three lens groups, in order from the object side, a first lens group of negative refractive power, a second lens group that includes a stop, and a third lens group of positive refractive power. The first lens group is at the object end of the retrofocus wide-angle lens and includes, in order from the object side, a plurality of negative lens components and a plurality of positive lens components. The first lens group includes three lens groups with particular lens features, the first of which, from the object side, also includes two lens groups with particular features. Various combinations of lens elements satisfy two conditions for ratios of absolute values of focal lengths for the various combinations of lens elements that assist in achieving excellent imaging.

Abstract: An extender optical system, for insertion between a photographic main lens and a camera body for changing the focal length of the lens system as a whole to the long focus side, is formed of, in order from the object side, a first lens group having negative refractive power, a second lens group formed of a single negative lens, and a third lens group having positive refractive power. The negative lens that constitutes the second lens group is made to move in directions that are normal to the optical axis so as to correct for what would otherwise be blurred images due to vibrations. Various conditions are preferably satisfied so as to ensure high image quality over the entire field of view.

Abstract: A retrofocus wide-angle lens is formed of only three lens groups, in order from the object side, a first lens group of negative refractive power, a second lens group that includes a stop, and a third lens group of positive refractive power. The first lens group is at the object end of the retrofocus wide-angle lens and includes, in order from the object side, a plurality of negative lens components and a plurality of positive lens components. The first lens group includes three lens groups with particular lens features, the first of which, from the object side, also includes two lens groups with particular features. Various combinations of lens elements satisfy two conditions for ratios of absolute values of focal lengths for the various combinations of lens elements that assist in achieving excellent imaging.

Abstract: An adaptor lens is provided for attachment between a lens of a camera and a camera body, in order to provide the camera with adaptor lens attached, a smaller effective screen size than the camera without the adaptor lens attached. The adaptor lens is formed of, in order from the object side, a front lens group and a rear lens group. The front lens group is formed of, in sequential order from the object side, a negative lens element and at least one meniscus lens element with its concave surface on the object side. The rear lens group is formed of, in sequential order from the object side, a positive lens element with a convex surface on the object side, and a negative lens element. Various conditions are, preferably, satisfied in order to maintain favorable correction of axial chromatic aberration and lateral color.

Abstract: A retro focus type wide-angle lens comprises a front group having a negative refracting power and a rear group having a positive refracting power. The front group comprises a first lens made of a negative meniscus lens, a second lens made of a biconvex lens, a third lens made of a negative meniscus lens, and a fourth lens made of a positive meniscus lens. The rear group comprises a cemented lens in which a fifth lens made of a negative lens and a sixth lens made of a positive lens are cemented together, and a seventh lens made of a positive lens. This wide-angle lens further satisfies predetermined conditional expressions.

Abstract: An adaptor lens is provided for attachment between a lens of a camera and a camera body, in order to provide the camera with adaptor lens attached, a smaller effective screen size than the camera without the adaptor lens attached. The adaptor lens is formed of, in order from the object side, a front lens group and a rear lens group. The front lens group is formed of, in sequential order from the object side, a negative lens element and at least one meniscus lens element with its concave surface on the object side. The rear lens group is formed of, in sequential order from the object side, a positive lens element with a convex surface on the object side, and a negative lens element. Various conditions are, preferably, satisfied in order to maintain favorable correction of axial chromatic aberration and lateral color.

Abstract: An attachment lens for attachment to the object side of a main camera lens in order to enable the taking of short distance shots is disclosed. The attachment lens consists of three lens elements of positive, negative, and positive refractive power, in order from the object side. The first lens element and the second lens element are coupled to form a single component. The first lens element has a convex surface on the object side. The second lens element can be of meniscus shape with its convex surface on the object side, plano-concave, or biconcave so long as its curvature matches the image side of the first lens element so that the first lens element and the second lens element may be coupled together to form a single component. Preferably, one or more specified conditions are satisfied in order maintain favorable correction of aberrations.

Abstract: A retro focus type wide-angle lens comprises a front group having a negative refracting power and a rear group having a positive refracting power. The front group comprises a first lens made of a negative meniscus lens, a second lens made of a biconvex lens, a third lens made of a negative meniscus lens, and a fourth lens made of a positive meniscus lens. The rear group comprises a cemented lens in which a fifth lens made of a negative lens and a sixth lens made of a positive lens are cemented together, and a seventh lens made of a positive lens. This wide-angle lens further satisfies predetermined conditional expressions.

Abstract: An attachment lens optical system for extending a focal length of a camera lens and balancing axial chromatic aberrations of the camera lens comprises, in order from the object side, a first lens group having a negative power single lens element, a second lens group including a cemented doublet of a biconcave lens element and a biconvex lens element, a positive power third lens group including three lens elements, and a negative power fourth lens group including a cemented doublet of two lens elements.

Abstract: A four-group zoom lens of positive, negative, positive or negative, and positive refractive power, respectively, is disclosed wherein the second lens group moves to vary the zoom ratio and the third lens group moves in order to keep the image surface at a fixed position during zooming, wherein the zoom lens has a high optical performance over the entire range of zoom and greatly mitigates ghost images by satisfying a first condition, and avoids unacceptable lateral chromatic aberrations by satisfying a second condition.

Abstract: An attachment lens optical system equipped with an oscillation isolating feature for extending a focal length of a camera lens comprises, in order from the object side, a negative power first lens group having three lens elements, a negative power second lens group having three lens elements, and a third lens group having two lens elements, at least one of the first to third lens groups being movable in a direction perpendicular to an axis of the attachment lens optical system so as to cancel an image oscillation caused due to a shake of the imaging device.

Abstract: In a master lens section having an imaging effect, a luminous divergent lens portion having a negative refracting power is disposed on the object side of an aperture stop, whereby Petzval sum is restrained from greatly becoming negative, thus keeping image quality in the periphery of the image surface from deteriorating. In a master lens group M, a concave lens L.sub.18 a having a negative refracting power is disposed on the object side of an aperture stop 2, thus decreasing the distance between a zoom lens second group Z2 and the concave lens L.sub.18 at the wide-angle end, so that the incident luminous flux moderately diverges at an early stage, thus restraining Petzval sum from becoming greatly negative.

Abstract: A zoom lens includes a front lens group, a zooming lens group and relay lens group arranged in this order from the object side. The zoom lens is focused by moving at least a part of the front lens group and a part of the relay lens group in the direction of the optical axis. The front lens group is moved so that the focusing movement of the front lens group for a given object point is smaller as compared with that by which the front lens group should be moved when the zoom lens is focused by moving solely the front lens group and the focusing error generated by such a movement of the front lens group is larger in the wide-side than the tele-side, and a part of the relay lens group is moved to correct the focusing error.

Abstract: A zoom lens system consists of a first lens group G1 which has a positive refracting power and is held stationary when zooming, second, third and fourth lens groups G2, G3 and G4 which are moved when zooming, a stop and a fifth lens group G5 for image-forming. The first to fourth lens groups G1 to G4, the stop and the fifth lens group G5 are arranged in this order from the object side. The second to fourth lens groups G2 to G4 are moved during zooming with the distance between the third and fourth lens groups G3 and G4 controlled so that the fluctuation in coma with change in the zooming position is well suppressed.

Abstract: Described herein is a retrofocus type wide angle lens system composed of a front group with a negative power and a rear group with a positive power, in which the front group is divided into a fixed group starting with a negative meniscus lens having a convex surface on the object side and terminating with a negative lens element having a concave surface on the image-forming side, and a corrective group starting with a positive lens element having a convex surface on the object side. The fixed group which is constituted by larger and heavier lens elements is held stationary relative to an image forming plane, while the corrective group of smaller and light-weight lens elements is movable in the direction of the optical axis concurrently with the rear group to vary the width of the air space between the respective groups at the time of focusing, thereby effectively correcting various aberrations which would otherwise occur in a conspicuous degree in infinite to near distance focusing.