Abstract: A beam splitter (24) for splitting light in a wavelength range of about 500 nm to about 600 nm is arranged in a relay optical system of a taking lens (12). A green light beam reflected from the beam splitter (24) is directed through a relay lens (R3) to a focusing state determination imaging unit (26). The imaging unit (26) comprises three imaging elements (A, B, C) for capturing the directed green light beam to determine the focusing state. Thus, a device for determining the focusing state of the taking lens is provided, in which the green light beam is separated as an object light for determining the focusing state from the object light entering the taking lens (12), so that the focusing state can be determined with high accuracy on the basis of the high-frequency components of the image signal generated by capturing the green light beam by means of the imaging elements (A, B, C) having different optical path lengths.

Abstract: The auto focus system obtains focus information on a lens-interchangeable camera body of a TV camera and sends the focus information to a lens apparatus mounted on the camera body. The lens apparatus controls an auto focus based on the focus information. It is thereby possible to control the focus on adequate conditions according to optical specifications of the lens apparatus and so on.

Abstract: A focus detecting system for determining the focus state of an imaging lens, such as a camera lens, is disclosed. Object light not forming an image for image production is deflected along an optical axis through a relay lens to a focus state detection unit that includes image detecting elements with light receiving surfaces that are equidistant in front of and behind a position conjugate with a light receiving surface for image production. Either the relay lens or the focus state detection unit is moveable along the optical axis to vary how far the light receiving surfaces are out of focus. A diaphragm opening of the imaging lens determines if and by how much the relay lens and focus state detection unit are relatively moved. Evaluation values of the out of focus amount are compared in order to control focusing of the imaging lens.

Abstract: An autofocus system for an imaging device that includes an image detecting element for image production at a focused image plane of an adjustable focus imaging lens that also includes four image detecting elements for focus detection arranged in pairs that are equidistant in front of, and behind, planes that are conjugate with the focused image plane. One pair of image detecting elements for focus detection are farther than the other pair from the conjugate planes and may be used alone for focusing based on the stop value or focal length of the adjustable focus imaging lens. Alternatively, the other pair of image detecting elements may be used for more accurate focusing after the one pair of image detecting elements is used. The use of two pairs of image detecting elements at different distances from the focused image plane provides accurate focusing over a wide range of object distances.

Abstract: A focus detecting system for determining the focus state of an adjustable focus imaging lens includes a first beamsplitter for separating light for image production and light for detection of the focus state of the adjustable focus imaging lens in the ratio of 2:1. Only two focus state detecting elements are used, each of which receives from a second beamsplitter one-sixth of the amount of light that enters the adjustable focus imaging lens. Light receiving surfaces of the two focus state detecting elements are equidistant from image planes that are conjugate to an image plane for image production. The focus state detecting elements operate in the contrast mode using high frequency components of video signals to produce evaluation values that indicate an in-focus state of the imaging system by being equal. In one embodiment, the images that the focus state detecting elements detect are not reverted.

Abstract: An imaging optical system includes at least one ghost image prevention element. Ghost images are prevented even when the imaging optical system includes an optical element that has at least one planar surface that is generally orthogonal to an optical axis of the imaging optical system, and is located in a light flux area with at least a central portion of the light flux area being generally parallel to the optical axis. The ghost image prevention element is especially useful in video cameras and digital cameras that use an image sensor having a planar surface that exhibits a high coefficient of reflection. The ghost image prevention element includes one planar surface, that is “tightly bound” to the planar surface of the optical element, and another surface that is curved so as to satisfy a given condition. The curved surface diffuses light that would otherwise contribute to a ghost image.

Abstract: A zoom lens having both manual mode and auto focus mode of focus adjustment. The zoom lens includes, in order from the object side, a focus portion, a zoom portion, and a main portion. Zooming is accomplished by moving some or all of the lens elements in the zoom portion along the optical axis. What would otherwise be a fluctuation of the image surface with change of object distance is corrected in manual mode by manually moving some or all of the lens elements of the focus portion along the optical axis based on visual observation of the object through the zoom lens as the adjustment is made. In auto focus mode, what would otherwise be a fluctuation of the image surface with change of object distance is corrected by micro-vibrating some or all of the lens elements of a lens group in the light path following the focus portion.

Abstract: The focusing state determining adapter is detachably mounted between an interchangeable taking lens and a camera body in a camera system. The focusing state determining adapter includes a focus-imaging element and a beam splitter, which divides the subject light entering through the taking lens into light entering the focus-imaging element and light entering the camera body. The focusing state determining adapter determines the focusing state of the taking lens according to an image captured by the focus-imaging element.

Abstract: A zoom lens having both manual mode and auto focus mode of focus adjustment. The zoom lens includes, in order from the object side, a focus portion, a zoom portion, and a main portion. Zooming is accomplished by moving some or all of the lens elements in the zoom portion along the optical axis. What would otherwise be a fluctuation of the image surface with change of object distance is corrected in manual mode by manually moving some or all of the lens elements of the focus portion along the optical axis based on visual observation of the object through the zoom lens as the adjustment is made. In auto focus mode, what would otherwise be a fluctuation of the image surface with change of object distance is corrected by micro-vibrating some or all of the lens elements of a lens group in the light path following the focus portion.

Abstract: A zoom lens having only five lens groups of positive, negative, negative, positive and positive refractive power, respectively, in order from the object side. The focal distance is varied by shifting the second and third lens groups, in order from the object side, along the optical axis, and a middle sub-assembly in the first lens group is shifted along the optical axis in order to correct for what otherwise would be a shifting in the image plane as the distance to the object is varied. The first lens group is formed of three sub-assemblies, with the sub-assembly nearest the object side having negative refractive power and being fixed in position, the middle sub-assembly having positive refractive power and shifting as discussed above, and the sub-assembly nearest the image-side having positive refractive power and being fixed in position.

Abstract: A compact zoom lens having only four lens groups is provided which changes power by shifting a second lens group from the object side along the optical axis, and stabilizes the image plane position by shifting a fourth lens group from the object side along the optical axis. By satisfying three prescribed conditions, magnification of the image is prevented from decreasing for objects at very near distances, and aberrations are favorably corrected so as to provide for high quality imaging over the entire range of zoom for all object distances. At least one lens element has an aspherical surface.

Abstract: An inexpensive, high performance zoom lens includes, as measured from the object side, a negative first lens group and a positive second lens group. The overall length of the zoom lens is reduced by making one of the lens element surfaces of the first lens group G.sub.1 aspherical. A lens element in the second lens group is designed to be a biconvex lens with the same absolute value of radii of curvature, to thereby make the zoom lens inexpensive to produce and assemble.

Abstract: A second lens group is divided into a negative second A lens group and a positive second B lens group, and the distance between the second A and B lens groups is made variable so as to correct a fluctuation in aberration caused by a change in focal length, thereby reducing the size and weight of the whole lens system, while the fluctuation in performance is kept low in the whole zoom range and whole focus range. The second lens group is constituted by the second A lens group having a negative refracting power and the second B lens group having a positive refracting power. Upon a change in focal length, the distance between the second A and B lens groups is altered so as to suppress the fluctuation in aberration mainly in a middle range. Namely, in the second lens group having the highest refracting power, a surface spacing highly sensitive to the change in aberration is altered, whereby the aberration can be corrected with a favorable balance. Specifically, as indicated by the moving loci in FIG.

Abstract: A zoom lens comprising five lens groups is configured such that the total moving amount of the second lens group from the wide angle end to the telephotographic end is changed according to the object distance and that the fourth lens group is moved so as to correct zooming and focusing, whereby the imaging magnification is prevented from decreasing at the time of zooming even when the object distance changes. It comprises five lens groups respectively having positive, negative, negative, positive, and positive refractive powers. At the time of zooming, the first, third, and fifth lens groups (G1, G3, and G5) are fixed, while the second and fourth lens groups (G2 and G4) are made movable. The second lens group (G2) is moved in the optical axis direction so as to change the focal length of the whole system, while the fourth lens group (G4) is moved in the optical axis direction to correct fluctuation in the imaging position and to correct change in the imaging position caused by change in the object distance.

Abstract: In five constituent lens groups, the fourth lens group from the object side is made as a negative lens. This fourth lens group is moved in order to correct zooming and focusing, while predetermined conditional expressions are satisfied, thereby yielding a zoom lens which can attain a wide angle, a large zoom ratio, and favorable aberrations. This zoom lens has five groups respectively composed of positive, negative, positive, negative, and positive lens groups. At the time of zooming, the first, third, and fifth lens groups G1, G3, and G5 are fixed, while the second and fourth lens groups G2 and G4 are made movable. As the second lens group G2 is moved in the optical axis direction, the focal length of the whole system is changed. As the fourth lens group G4 is moved in the optical axis direction, fluctuation in imaging position is corrected while change in the imaging position due to change in object distance is corrected.

Abstract: A zoom lens system includes first to fifth lens groups arranged in this order from the object side. The first, third and fifth lens groups are fixed. The second lens group is moved in the direction of the optical axis of the zoom lens system when zooming the zoom lens system and the fourth lens group is moved in the direction of the optical axis to correct change in the image position due to the zooming and to correct change in the image position due to change in the object distance. The first lens group has a positive refracting power, the second lens group has a negative refracting power, the third lens group has a negative refracting power, the fourth lens group has a positive refracting power and the fifth lens group has a positive refracting power.

Abstract: In five-constituent lens groups, the fourth lens group from the object side is made as a positive lens. This fourth lens group is moved in order to correct zooming and focusing, while predetermined conditional expressions are satisfied, thereby realizing a zoom lens which can attain a wide angle and a high zoom ratio while favorably correcting various kinds of aberration. This zoom lens has five groups respectively composed of positive, negative, positive, positive, and positive lens groups. At the time of zooming, the first, third, and fifth lens groups G1, G3, and G5 are made stationary, while the second and fourth lens groups G2 and G4 are made movable. As the second lens group G2 is moved in the optical axis direction, the focal length of the whole system is changed. As the fourth lens group G4 is moved in the optical axis direction, the fluctuation in imaging position is corrected and the change in the imaging position due to change in object distance is corrected.

Abstract: A photographic lens apparatus secures a sufficiently large back focus while sufficiently distancing the exit pupil position from the image-forming surface. From the object side along an optical axis L, a stop, a first lens, a second lens, a third lens having a meniscus form, and a fourth lens group, in which a lens having a negative refractive power and a lens having a positive refractive power are cemented together to yield a positive refractive power, are successively disposed. Refractive index n.sub.1 and abbe number .nu..sub.1 of the first lens, abbe number .nu..sub.2 of the second lens, radius of curvature r.sub.7 of the surface facing the object and radius of curvature r.sub.8 of the surface facing the image in the third lens, abbe number .nu..sub.4 of the lens having the negative refractive power and abbe number .nu..sub.5 of the lens having the positive refractive power in the fourth lens group, focal length f.sub.

Abstract: A zoom lens system consists of a positive first lens group G1, a negative second lens group G2, a stop, a positive third lens group G3, a positive fourth lens group G4 and a positive fifth lens group G5 arranged in this order from the object side. The second and fourth lens groups G2 and G4 are moved with the other lens groups G1, G3 and G5 fixed when zooming. The focal length of the total lens system is changed by moving the second lens group G2 along the optical axis and the change in the image-forming position generated by the movement of the second lens group G2 is compensated for and the zoom lens system is focused by moving the fourth lens group G4 along the optical axis.The following formulae (1) and (2) are satisfied,1.1<f.sub.w(G4+G5) /(f.sub.w .multidot.f.sub.t).sup. 1/2 <1.3(1)1.2<f.sub.G3 /(f.sub.w .multidot.f.sub.t).sup. 1/2 <1.8 (2)wherein f.sub.w(G4+G5) represents the combined focal length of the fourth and fifth lens groups G4 and G5 at the wide-side end, f.sub.

Abstract: A miniature fixed-focal-length lens system includes a lens group which consists of a plurality of lenses and has a positive refracting power and a stop disposed on the object side of the lens group. The lens nearest to the object in the lens group is a meniscus lens which is concave to front and has a positive refracting power and the lens remotest from the object in the lens group is a lens which is convex to rear and has a positive refracting power.