Konishiroku Photo Industry Co., Ltd.

Shozo Ishiyama

Tadashi Kojima

Hisao Fujita

Makoto Banno

Norikazu Arai

When a zoom lens system is focused by moving a lens other than the foremost lens group, the advancing amount of the focusing lens varies according to the variation in the focal length even whyen focusing on an object at the same object distance. When a zoom lens system is zoomed to a certain focal length, the object distance and advancing amount of the focusing lens has a relationship expressed by a function resembling a logarithmic function. The present invention enables one to focus a zoom lens system using only one movement amount curve by arranging to move the focusing lens along the movement amount curve, utilizing different portions of the movement amount curve according to the amount of zooming.

Focusing means for a zoom lens group

The present invention relates to a zoom lens system having a new structure for use with still cameras, which is wide magnification-variable and compact whose zoom ratio is about three times. A positive third lens group of a conventional zoom lens comprising three lens group, i.e. positive, negative and positive is divided into two positive lens groups to thereby decrease the refractive power of each lens group and an airspace therebetween being increased and decreased, whereby enhancing the effect of magnification-variation or rendering it possible to be utilized for correction of aberration. Further, a positive lens group having a weak refractive power is arranged between image planes to effect correction of aberration. As a result, there is obtained a zoom lens system having a new arrangement of refractive power in order of positive, negative, positive, positive and positive.

Zoom lens

A zoom lens system composed of five lens groups having power of positive, negative, positive, negative and positive, among various types of the zoom lens system. The zoom lens system particularly of the type in which all of five lens groups are movable is advantageous in designing the zoom lens system. However, since these five lens groups are moved independently one another, it becomes complicated to design the barrel. In accordance with the present invention, a third positive lens group and one of the other positive lens groups may be moved integrally to effect zooming, such that the moving mechanism for the four moving groups may be used in designing the barrel, thus simplifying the construction of the barrel.

Compact, wide magnification-variable zoom lens system

A large-aperture single lens with aspherical surfaces to be used as a pickup lens for video disks, especially for tracking the video disk by directly moving the pickup lens. It is preferable that the single lens is made of plastic material in order to make it compact and light in weight. Both refractive surfaces of the single lens are arranged to have positive refractive powers in order to make the working distance of the lens long. Spherical aberration of the single lens is corrected to the degree that the diameter of the circle of confusion thereof is decided approximately by diffraction of light. Both refractive surfaces of the single lens are formed as aspherical surfaces and the shapes of the refractive surfaces are determined so as to correct aberrations including the sine condition to the required range, by taking the error to be caused at the time of manufacture into consideration.

Large-aperture single lens with aspherical surfaces

A wide magnification-variable range zoom lens system having a short total length and a small diameter permitting zooming from the wide angle to a long focal length comprises five lens groups having positive, negative, positive, negative and positive focal lengths respectively, a partial lens system consisting of said first and second lens group having a negative focal length over the entire zooming region, a partial lens system consisting of said third through fifth lens groups having a positive focal length, all of said lens groups moving along the optical axis to contribute to the variation of focal length of said zoom lens system, and said first lens group widely moving toward the object side when total focal length of the zoom lens system varies from the shortest to the longest.

Wide magnification-variable range zoom lens system

A compact zoom lens of mechanical compensation type is described which comprises first, second, third and fourth lens groups arranged so that variation of image position caused when the second lens group is moved along the optical axis for the purpose of varying the focal length is compensated by moving the third lens group so as to form a locus of points concave toward the object side. The zoom lens as a whole is made compact by compactly arranging the vari-focal lens groups, which comprise the first through third lens groups, by making the amounts of movements of the second and third lens groups small and by arranging the vari-focal lens group itself so that the focal length of the fourth lens group becomes short.

Growing community of inventors

Hino, Japan

Shozo Ishiyama