Abstract: A three-group zoom lens is provided of negative, positive, and positive refractive power, respectively, in the order from the object side. The first lens group is formed of a negative lens element and a positive lens element, the second lens group includes a stop for controlling the brightness of an image, two positive lens elements, and a negative lens element, and each lens group includes at least one aspherical surface. When zooming from the wide-angle end to the telephoto end, the first lens group is moved nearer the second lens group, and said second and third lens groups are moved continuously toward the object side. When focusing from an object at infinity to an object nearby, the third lens group is moved toward the object side. Specified conditions are satisfied in order to ensure that the exit pupil is an appropriate distance from the image plane for efficient light detection, while providing a zoom lens having an FNO of approximately 2.8 or less and a zoom ratio of 2.

Abstract: A negative first lens group, a positive second lens group, and a positive third lens group are provided in sequence from an object side of a zoom lens. An aperture is provided in the second group of lenses. At the time of zooming operation, the three groups of lenses independently move over an optical axis X. The second group of lenses is constituted of, in sequence from the object side, a biconvex lens group 2A; a lens group 2B formed by cementing two or more lenses together; an aperture; a lens group 2C formed by cementing together two or more lenses; and a lens group 2D whose convex side is oriented toward the image surface side.

Abstract: A projection zoom lens includes a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power, which are arranged in that order from a screen side toward an image plane side along an optical axis. The first and the fourth lens group are kept stationary, and the second and the third lens group are moved along the optical axis to vary power from a limit wide angle power toward a limit telephoto power. The second lens group includes a 2nd-group 1st positive lens, a 2nd-group 1st compound lens formed by joining a 2nd-group 2nd positive lens having a convex surface on the image plane side and a 2nd-group 1st negative lens having a concave surface on the screen side, and a 2nd-group 3rd positive lens arranged in that order from the screen side toward the image plane side.

Abstract: The present invention provides a zoom lens suitable for an image pickup system using a solid-state image pickup element. In detail, the zoom lens disclosed in the present invention includes three lens units having negative, positive, and positive optical power in order from an object side to an image side, in which zooming is performed by moving each lens unit in the direction of an optical axis. The first lens unit has at least one positive lens and at least one negative lens. The second lens unit has at least one positive lens and at least one negative lens, in which a plastic lens of positive optical power is disposed on the side closest to the object.

Abstract: A zoom lens which suppresses variations of an exit pupil and is telecentric on the image side in the whole range of zooming is to be disclosed.

Abstract: The invention concerns a compact optical system that is made up of a reduced number of lens elements with a bendable optical path and so is compatible with miniature image pickup devices used with cellular phones, etc. The image pickup lens of the invention comprises, in order from its object side, a first lens element L101 having negative refracting power, a second lens element L102 having positive refracting power, a stop S1, a third lens element L103 having negative refracting power and a fourth lens element L104 having positive refracting power, and satisfies the following conditions (1) and (2).

Abstract: A zoom lens with a slim and compact design has arranged in sequence from the object side to the image plane side a first lens group having a negative refractivity, a second lens group having a positive refractivity, and a third lens group having a positive refractivity. The first lens group is formed from a first lens having a negative refractivity and a second lens having a positive refractivity. The second lens group is formed from a third lens having a positive refractivity and a fourth lens and a fifth lens. The fourth and fifth lens are joined together and have a negative refractivity. The third lens group is formed from a sixth lens having a positive refractivity. The zoom lens has a short length when retracted and extended, and a design that is compact and thin.

Abstract: The disclosed zoom lens includes a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power in order from an object side to an image side. The zoom lens has a shorter interval between the first lens unit and the second lens unit and a longer interval between the second lens unit and the third lens unit on a telephoto end than an interval between the first lens unit and the second lens unit and an interval between the second lens unit and the third lens unit on a wide angle end, respectively.

Abstract: A zoom lens system includes a negative first lens group, a positive second lens group, a negative third lens group, and a positive fourth lens group, and satisfies the following conditions:

Abstract: The present invention provides a zoom lens system suitable for an image gathering system using a solid-state imaging device, having a zoom ratio of about three, a small total lens length, and superb optical performance. According to one aspect, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. Zooming is carried out by varying distances between adjacent lens groups. The first lens group includes two negative lens elements and a positive lens element. The second lens group includes three lens elements consisting of a first positive lens element, a second positive lens element, and a negative lens element. The third lens group includes at least one positive lens element. Predetermined conditional expressions are satisfied.

Abstract: A zoom lens system includes a positive first lens group, and a negative second lens. Zooming is performed by varying the distance between the first lens group and the second lens group. The first lens group includes a negative first sub lens group and a positive second sub lens group. The zoom lens system satisfies the following conditions: 5.0<ft/f1<7.0  (1) 0.9<|fw/f1a|<1.8  (2) wherein ft designates the focal length of the entire zoom lens system at the long focal length extremity; f1 designates the focal length of the first lens group; fw designates the focal length of the entire zoom lens system at the short focal length extremity; and f1a designates the focal length of the first sub lens group of the first lens group.

Abstract: A zoom lens is constructed with, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including a cemented lens of positive optical power as a whole disposed on the most image side of the second lens unit, and a lens having a concave surface facing the image side and adjoining a surface on the object side of the cemented lens, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.

Abstract: A zoom lens system includes a negative first lens group, a positive second lens group, and a negative third lens group. Zooming is performed by moving the first through third lens groups along the optical axis, and the zoom lens system satisfies: 0.03<(dW12−dT12)/fW<0.1   (1); −4<fT/f1G<−2   (2); wherein dW12 and dT12 designate the distance between the most image-side surface of the first lens group and the most object-side surface of the second lens group, at the short focal length extremity and long focal length extremity, respectively; fW and fT designate the focal length of the entire zoom lens system at the short focal length extremity and the long focal length extremity, respectively; and f1G designates the focal length of the negative first lens group.

Abstract: A taking lens device has a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units, and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. The zoom lens system includes, from the object side to the image side a first lens unit that has a negative optical power, that is composed solely of a single negative lens element having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming, and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, and that is moved along the optical axis during zooming. Moreover, the following conditional formulae are fulfilled: 0.3<t1/Y′<1.5 and 1.

Abstract: A zoom lens system having multiple lens units including, sequentially in a direction from an enlargement side thereof toward a reduction side thereof, a first lens unit having a negative optical power, a second lens unit having a positive optical power, a third lens unit having a positive optical power, a fourth lens unit having a negative optical power, and a fifth lens unit having positive optical power. Additionally, during a zoom operation from a longest focal length condition to a shortest focal length condition, the zoom lens system can function such that the first lens unit and the fifth lens unit can remain stationary, while the second, third and fourth lens units are able to move.

Abstract: A zoom lens includes a lens unit A of negative refractive power, and a lens unit B of positive refractive power disposed on an image side of the lens unit A. The lens unit B includes two cemented lens components and consists of not more than five lens elements. Then, the separation between the lens unit A and the lens unit B varies during zooming.

Abstract: The present invention provides a compact zoom lens system suitable for a video camera and a digital still camera using a solid-state imaging device, having a zoom ratio of 3.5 or more, an angle of view in a wide-angle end state of about 60°, and superb optical performance. According to one aspect, in order from an object side, a first lens group has negative refractive power, a second lens group has positive refractive power, and a third lens group has positive refractive power. The front principal point of the second lens group is located to the object side of the most object side surface of the second lens group. The distance between the first and second lens group is decreased and the distance between the second and third lens group is increased upon zooming from a wide-angle end state to a telephoto end state. Predetermined conditional expressions are satisfied.

Abstract: An optical system includes a diffractive optical element in which a phase given to incident light from an optical axis toward the peripheral part in the radial direction is not reversed in an effective area and an absolute value of optical power on the optical axis is made minimum. In the optical system, chromatic aberration of magnification of a high order is satisfactorily corrected and flare caused by additional diffraction light (unnecessary diffraction light) is suppressed to as minimum as possible while maintaining a high imaging performance up to peripheral part of a field angle.

Abstract: The present invention provides a compact zoom lens system suitable for a video camera and a digital still camera using a solid-state imaging device, having a zoom ratio of 3.5 or more, an angle of view in a wide-angle end state of about 60°, and superb optical performance. According to one aspect, in order from an object side, a first lens group has negative refractive power, a second lens group has positive refractive power, and a third lens group has positive refractive power. The front principal point of the second lens group is located to the object side of the most object side surface of the second lens group. The distance between the first and second lens group is decreased and the distance between the second and third lens group is increased upon zooming from a wide-angle end state to a telephoto end state. Predetermined conditional expressions are satisfied.

Abstract: A zoom lens comprises five lens groups including second, third and fourth lens groups which are moved in a given relationship relative to one another and relative to first and fifth lens groups which are stationary during zooming to continuously change the focal length and compensate a shift of image plane of the zoom lens such that the second and third lens groups move closer to each other as the zoom lens changes the focal length to the telephoto end satisfies at least the following conditions: −1.7<F1/F<−0.3 0.7<F2/F<2.2 1.5≦F5/F<2.2 where F is the overall focal length of the zoom lens at a wide angle end; F1 is the focal length of the first lens group; F2 is the focal length of the second lens group; F5 is the focal length of the fifth lens group.

Abstract: A retro-focus-type camera lens is disclosed that is formed of, in order from the object side: a front lens group having negative refractive power, a diaphragm, and a rear lens group having positive refractive power. The front lens group is formed of, in order from the object side, a positive lens element and two negative lens elements, and the rear lens group is formed of, in order from the object side, a positive lens element, two sets of lens elements that are cemented together to form two joined lenses, and a positive lens element. Various conditions are preferably satisfied in order to provide a lens having an image angle of about 38°, an F number of about 1.4, and which suppresses the occurrence of color shading while providing a sufficient back focus to insert a color separation optical system between the retro-focus-type camera lens and the image plane.

Abstract: There are provided a zoom lens system comprising, in order from a more distant conjugate point, a first lens unit of a negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth and fifth lens units, and at least one diffraction optical element.

Abstract: The object of the present invention is to provide a zoom lens system being extremely reduced size such as a standard single focal length lens, having very few number of lens elements, being ultimately reduced cost, having a zoom ratio about 2.2, and also having high optical performance without using any aspherical surface. The zoom lens system has, in order from an object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, and performs zooming by changing an air space between the first lens group G1 and the second lens group G2. The first lens group comprises, in order from the object side, a negative lens group Ln consisting of one or two negative lens elements and a positive lens L12 having a convex surface facing to the object side. All surfaces consisting of the first lens group G1 are spherical or plane surfaces. Predetermined conditional expressions are satisfied.

Abstract: An optical device has zoom lens system comprised of plurality of lens units which achieves zooming by varying unit-to-unit distances and an image sensor that converts optical image formed by zoom lens system into an electrical signal. The zoom lens system is comprised of, from the object side, at least first lens unit having a negative optical power and second lens unit having a positive optical power. Following conditional formulae are fulfilled: 2<|f1/fw|<4, and 0.058<(tan &ohgr;w)2×fw/TLw<0.9, where f1 represents focal length of first lens unit, fw represents focal length of entire optical system at wide-angle end, tan &ohgr;w represents half view angle at wide-angle end, and TLw represents total length (the distance from first vertex to image plane) at wide-angle end.

Abstract: A variable-focus lens system includes a negative front lens group, and a positive rear lens group. The focal length of the variable-focus lens system is varied by changing the distance between the front and said rear lens groups.

Abstract: A projection lens has five optical groups, labeled OI to OV, having effective focal lengths fI to fV, respectively. The optical groups move on an optical axis to perform zooming and focussing functions. The projection lens has a total of at least thirteen lenses, which may be labeled L1 to L13, having focal lengths f1 to f13, respectively, Abbe numbers V1 to V13, respectively, and indices of refraction N1 to N13, respectively. Optical group OI has the first three lenses, L1 to L3. Optical group OII , has the next two lenses, L4 and L5. Optical group OIII has the next three lenses, L6 to L8. Optical group LIV has lens L9. Finally, optical group OV has the remaining lenses, L10 to L13, of which L10 to L12 combine to form a triplet. The lens groups satisfy the following conditions: −0.45<(f11/fV)<−0.25 V10+V12−2V11>44 2N11−N10−N12>0.5 0.5<(fN+fP)/(fP)<0.

Abstract: An inner-focusing type super wide-angle zoom lens system consisting of two lens groups, a negative lens group and a positive lens group, with the maximum angle of view of more than 100° and the zoom ratio of 1.7 or more is provided. The zoom lens system includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power. Zooming operation is carried out by changing the interval between the first lens group G1 and the second lens group G2. The second lens group consists of, in order from the object side, a front second lens group G2a having a positive refractive power and a rear second lens group G2b having a positive refractive power. Focusing operation from infinity to near object is carried out by moving the front second lens group G2a to the image side. Predetermined conditional expressions are satisfied.

Abstract: A zoom lens system including a first through third lens groups. The combined power of the first and second lens groups is positive. Upon zooming from the short focal length extremity towards the long focal length extremity, all the three lens groups are moved from the image towards the object. The zoom lens system satisfies the following conditions: 0.01<(d12W−d12T)/fW<0.1  (1); 3.5<fT/f12W<6.0  (2); 4.0<fT/|f3G|<8.

Abstract: A high-resolution variable focus lens system that has an extra-long back focal length with a telecentric design. The lens system includes three groups of lenses between an object (screen) and an image (a liquid crystal panel). The first group of lenses, comprising three lenses and having a negative power, is used for focusing and zooming of the lens system. The second group of lenses, comprising two lenses and having also a negative power, is used for zooming of the lens system. The third group of lenses, comprising six lenses and having a positive power, is similarly used for zooming of the lens system.

Abstract: A wide-angle zoom lens is provided having only three lens groups of, in order from the object side, negative, positive, and positive refractive power, respectively. The fist lens group is formed of only two lens elements, each of negative refractive power. The wide-angle zoom lens is compact and achieves high optical performance over the entire range of zoom by satisfying predetermined conditions. When power is varied during zooming, the first lens group and the second lens group are moved along the optical axis, and the third lens group remains in a fixed position. During focusing, the first lens group is moved along the optical axis.

Abstract: A small-sized, large-aperture, wide-angle zoom lens, having three lens groups of negative, positive, and positive refractive power, respectively, in order from the object side, is disclosed. The FNO of the zoom lens remains constant during zooming. The second lens group includes, in order from the object side, a biconvex lens element, a negative lens element having a concave surface on the object side, a positive lens element having a convex surface on the image side, and a biconvex lens element. The first and second lens groups are moved along the optical axis during zooming, and the third lens group is fixed in position during zooming and includes a stop. Specified conditions are preferably satisfied in order to keep the focal length of the zoom lens short, to correct aberrations, and to keep manufacturing of the zoom lens practicable. Thus, bright, well-corrected images are obtained over the entire range of zoom.

Abstract: The invention relates to a zoom lens system of two-group construction, one lens for each group, which is less susceptible to aberration variations even upon zooming and can be much more increased in terms of lens aperture and zoom ratio. The zoom lens system of two-group construction comprises, in order from an object side thereof, a first lens group G1 having negative refracting power and a second lens group G2 having positive refracting power and in which a focal length thereof is varied by moving both the lenses while an optical axis separation therebetween is varied. The first lens group G1 consists of one concave lens having a strong concave surface directed toward an image plane side of the zoom lens system and formed of a homogeneous medium, and the second lens group G2 consists of one convex lens formed of a homogeneous medium. A stop S is located between the first lens group G1 and the second lens group G2.

Abstract: A zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object, and thereby zooming is performed by moving the first through third lens groups along the optical axis. The zoom lens system satisfies the following condition: 0.05<d12W/fW<0.35  (1) wherein d12W designates the distance between the first lens group and the second lens group at the short focal length extremity; and fW designates the focal length of the entire lens system at the short focal length extremity.

Abstract: A three-group zoom lens of negative, positive, and positive refractive power, in order from the object side. The first lens group is formed of two lens elements of negative and positive refractive power, respectively, the second lens group includes an aperture stop on its object side, and at least one surface in each of these lens groups is aspherical. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group decreases and both the second and the third lens groups move toward the object side. When changing the focus from an object at an infinite distance to a nearby object the position of the third lens group is shifted. When focused on an object at infinity, the distance between the second lens group and the third lens group is kept substantially constant when zooming from the wide-angle end to the telephoto end. The zoom lens has a zoom ratio of 2.

Abstract: A projection zoom lens system according to the present invention has a substantially telecentric incidence side and comprises a plurality of lens groups for behaving differently between a wide-angle end and a telephoto end, wherein at least one of two surfaces of a lens included in a first lens group located closest to a screen side has an aspheric surface. Since the lens closest to the screen has the largest diameter and the density of light rays becomes smallest among the lenses, it is possible to design the aspheric surface for correcting properly the light rays and reduce the correcting loads of the other lens groups constituting the projection zoom lens system so as to provide the compact and high performance zoom lens system.

Abstract: A wide-angle zoom lens system including a negative first lens group, a positive second lens group, a diaphragm, and a positive third lens group, in this order from the object; whereby upon zooming from the short focal length extremity towards the long focal length extremity, each lens group is arranged to move so that the space between the first and second lens groups and the space between the second and third lens groups are narrowed; and the diaphragm moves integrally with the third lens group. At least one negative lens element having a concave surface facing towards the image is provided in the first lens group, and the concave surface of the at least one negative lens element is an aspherical surface; and the wide-angle zoom lens system preferably satisfies the following condition; 0.8<X1/fS<2.

Abstract: A zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object, and thereby upon zooming, the three lens groups independently move along the optical axis. On the other hand, upon focusing, the first and second lens groups, which move independently upon zooming, move integrally along the optical axis.

Abstract: A zoom optical system provides a series of lens units designed to allow for zooming with minimal change in aberration resulting from the movement of the lens units. Each lens unit has a plurality of lens units. One embodiment has, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power wherein the second lens unit may have at least one gradient index lens element and the first lens unit is kept stationary during a change of magnification. Additional embodiments have more or fewer lens units and the refractive power of each lens unit is varied. In some embodiments, a lens unit other than the first lens unit is kept stationary.

Abstract: A zoom lens system according to the present invention includes a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from the object. The zoom lens system satisfies the following conditions: 4<fL/D1<6  (1) 1.0<|fL/f1|<1.3  (2) wherein fL designates the focal length of the entire zoom lens system at the long focal length extremity; D1 designates the distance, along the optical axis, from the most object-side to the most image-side lens surfaces of the first lens group; and f1 designates the focal length of the first lens group.

Abstract: A small-sized, large-aperture, wide-angle zoom lens, having three lens groups of negative, positive, and positive refractive power, respectively, in order from the object side, is disclosed. The FNO of the zoom lens remains constant during zooming. The second lens group includes, in order from the object side, a biconvex lens element, a negative lens element having a concave surface on the object side, a positive lens element having a convex surface on the image side, and a biconvex lens element. The first and second lens groups are moved along the optical axis during zooming, and the third lens group is fixed in position during zooming and includes a stop. Specified conditions are preferably satisfied in order to keep the focal length of the zoom lens short, to correct aberrations, and to keep manufacturing of the zoom lens practicable. Thus, bright, well-corrected images are obtained over the entire range of zoom.

Abstract: An inner-focusing type super wide-angle zoom lens system consisting of two lens groups, a negative lens group and a positive lens group, with the maximum angle of view of more than 100° and the zoom ratio of 1.7 or more is provided. The zoom lens system includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power. Zooming operation is carried out by changing the interval between the first lens group G1 and the second lens group G2. The second lens group consists of, in order from the object side, a front second lens group G2a having a positive refractive power and a rear second lens group G2b having a positive refractive power. Focusing operation from infinity to near object is carried out by moving the front second lens group G2a to the image side. Predetermined conditional expressions are satisfied.

Abstract: A three-group zoom lens is provided of negative, positive, and positive refractive power, respectively, in the order from the object side. The first lens group is formed of a negative lens element and a positive lens element, the second lens group includes a stop for controlling the brightness of an image, two positive lens elements, and a negative lens element, and each lens group includes at least one aspherical surface. When zooming from the wide-angle end to the telephoto end, the first lens group is moved nearer the second lens group, and said second and third lens groups are moved toward the object side. When focusing from an object at infinity to an object nearby, the third lens group is moved toward the object side. Specified conditions are satisfied in order to ensure that the exit pupil is an appropriate distance from the image plane for efficient light detection, while providing a zoom lens having an FNO of approximately 2.8 or less and a zoom ratio of 2.

Abstract: A three-group zoom lens has, from an object side, a first group lens having a positive power, a second group lens having a negative power and a third group lens consisting of a positive lens. The second lens group includes an aperture stop. When a distance to be focused is infinity, only the first lens group and the second lens group move for zooming. At least one positive lens included in the zoom lens has an aspherical surface whose positive power is greater at a portion farther from an optical axis thereof.

Abstract: The invention relates to a high-performance, large-aperture yet wide-angle zoom lens system that can be used with an electronic image pickup device in particular, a method for focusing the same. In particular, the invention is concerned with a high-performance, large-aperture yet wide-angle zoom lens system which has a zoom ratio of the order of 3 at a diagonal field angle of 75° at its wide-angle end, so that it can be used with a single-lens reflex camera using an electronic image pickup device with the number of pixels being of the order of 6,000,000. The zoom lens system comprises a first lens group G1 having negative refracting power, a second lens group G2 having positive refracting power, a third lens group G3 having negative refracting power, a fourth lens group G4 having positive refracting power and a fifth lens group G5 having positive refracting power. Upon movement of an object point, focusing is carried out with the fifth lens group G5.

Abstract: A wide-angle zoom lens is provided having only three lens groups of, in order from the object side, negative, positive, and positive refractive power, respectively. The fist lens group is formed of only two lens elements, each of negative refractive power. The wide-angle zoom lens is compact and achieves high optical performance over the entire range of zoom by satisfying predetermined conditions. When power is varied during zooming, the first lens group and the second lens group are moved along the optical axis, and the third lens group remains in a fixed position. During focusing, the first lens group is moved along the optical axis.

Abstract: A wide-angle zoom lens system including a negative first lens group, a positive second lens group, a diaphragm, and a positive third lens group, in this order from the object; whereby upon zooming from the short focal length extremity towards the long focal length extremity, each lens group is arranged to move so that the space between the first and second lens groups and the space between the second and third lens groups are narrowed; and the wide-angle zoom lens system preferably satisfies the following condition: 0.36<(D2S−D2L)/(fL−fS)<0.

Abstract: A zoom lens of the negative lead type includes, in order from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power consisting of one negative lens, and a fourth lens unit of positive refractive power consisting of one positive lens, wherein, during zooming from the wide-angle end to the telephoto end, all the lens units move along an optical axis in such a manner that the separation between the first lens unit and the second lens unit decreases, the separation between the second lens unit and the third lens unit increases and the separation between the third lens unit and the fourth lens unit decreases.

Abstract: A zoom lens system has, from the object side, a first lens unit, a second lens unit and a third lens unit. The first lens unit has a negative optical power as a whole. The second and third lens units have a positive optical power as a whole. In the zoom lens system, zooming is achieved by varying the distance between the first and second lens units, and at least one of the lens elements is a plastic lens element.

Abstract: A zoom lens for primary use with a projection screen television system is disclosed having five lens groups, in sequential order from the enlarging side, of negative, positive, positive, negative, and positive refractive power. The first lens group and the fifth lens group are fixed, and the axial positions of the second lens group, the third lens group, and the fourth lens group vary when zooming so as to provide a change in magnification and to correct for shifting of the image surface which otherwise would occur with zooming. Specified conditions are satisfied in order to provide a zoom lens that is compact, is well-corrected for aberrations over the entire range of zoom, has a sufficient back focus on the reducing side for insertion of lens components needed for projecting color images, is nearly telecentric on its reducing side, and provides a sufficiently bright image with a wide-angle of view.

Abstract: A zoom optical system provides a series of lens units designed to allow for zooming with minimal change in aberration resulting from the movement of the lens units. Each lens unit has a plurality of lens units. One embodiment has, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power wherein the second lens unit has at least one gradient index lens element and the first lens unit is kept stationary during a change of magnification. Additional embodiments have more or fewer lens units and the refractive power of each lens unit is varied. In some embodiments, a lens unit other than the first lens unit is kept stationary.