Zoom lens assembly

Abstract: A zoom lens assembly which comprises, in the successive order from the object side a first fixed lens group of a positive refractive power including a negative lens, a positive lens and a positive meniscus lens; a second movable lens group of a negative refractive power including a negative meniscus lens, a positive lens and a positive lens for effecting a variation of image magnification by moving along an optical axis of the zoom lens assembly; a third fixed lens group of a positive refractive power having at least one aspherical face and including a positive lens and a negative lens; and a fourth movable lens group of a positive refractive power including a lens having at least one aspherical surface and also including negative and positive lenses cemented together.

Description: BACKGROUND OF THE INVENTION (Field of the Invention) The present invention relates to a high performance zoom lens assembly for use with, for example, a video camera. (Description of the Prior Art) In recent years, demands have been made to provide a video camera not only with an easy-to-operate feature and a quick-to-operate feature, but also with a capability of presenting high quality images and an availability of multi-functions. To satisfy those demands, a high-resolution compact imaging device of 1/3 inch in size has been widely employed, and a compact imaging device of 1/4 inch in size is currently developed. Along therewith, a high-performance compact and light-weight zoom lens having a large aperture ratio is strongly desired for. Yet, not only is a reduction in cost desired for, but a realization of a high-magnification zoom lens employing a reduced number of component parts without sacrificing the high performance is also desired for. However, when it comes to a high-magnification zoom lens, not only are an increased lens diameter and an increased lens length required, but an increased number of lens elements is also required for accomplishing a strict correction of aberrations, resulting in an increase in manufacturing cost and also in size and weight to such an extent that the resultant zoom lens is not suited for use in a video camera for home use. Accordingly, the compact and light-weight zoom lens assembly currently largely employed in video cameras for home use and of a type comprising about 10 lens elements and having an F-number of about 1.4 to 2.0 has a zooming ratio of 6 to 8. Hereinafter, the prior art zoom lens assembly of the type referred to above and such as disclosed in, for example, EP-A- 405,856 or United States Patent No. 5,100,223, issued March 31, 1992 (based on Japanese Patent Application No. 1-169295) will now be discussed with reference to Fig. 2. The preamble of Claim 1 corresponds to EP-A- 405,856. Fig. 2 illustrates an optical system of the prior art zoom lens assembly for use with a video camera. The prior art zoom lens assembly comprises, in the order from left as viewed therein, a first lens group 21 forming an image forming unit, a second lens group 22 forming a zooming unit, a third lens group 23 forming a light condensing unit, a fourth lens group forming a focusing unit and a glass plate 25 which is an equivalent to a quartz filter and the faceplate of the image device or the like. Reference numeral 26 represents an image forming plane. The prior art zoom lens assembly shown in Fig. 2 operates in the following manner. The first lens group 21 fixed relative to the image forming plane 26 plays an image forming role, while the second lens group 22 movable along the optical axis of the zoom lens assembly to vary a magnification thereby to vary the focal length of the zoom lens assembly as a whole. The third lens group 23, which is a fixed lens group, acts to collect rays of light dispersed by the second lens group 22, while the fourth lens group 24 movable along the optical axis plays a focusing role. A change in position of the image resulting from a movement of the second lens group 22 during a zooming operation is compensated for by a movement of the fourth lens group 24 to keep the image focused on the image plane 26 at all times. The prior art zoom lens assembly of the type referred to above, however, has a problem in that it is difficult to correct aberrations over a zooming region and over a range of photo-taking distance, particularly, chromatic aberrations, when the zooming ratio of 10 is chosen and is therefore difficult to accomplish a high quality image. SUMMARY OF THE INVENTION The present invention has been developed to substantially eliminate the above discussed problem and is intended to provide an improved high performance zoom lens assembly having a zooming ratio of about 10 for use in a video camera which is compact in structure and capable of satisfactorily correcting various aberrations including chromatic aberrations, and also to provide the video camera utilizing the improved zoom lens assembly. To this end, a zoom lens assembly according to the present invention is as defined in Claim 1. More preferably, the fourth lens group includes a negative lens having a concave surface oriented towards the image forming plane and a positive lens having a convex surface oriented towards the object side, said negative and positive lenses being cemented together. Preferably, the zoom lens assembly of the present invention is to satisfy the following conditions. (1) 3.0 < f1/fW < 8.0 (2) 0.5 < ¦f2¦/fW < 1.6 (3) 2.0 < f3/fW < 7.0 (4) 2.0 < f4/fW < 5.0 (5) 0.02 < d14/f4 <1.0 (6) 0.3 < r11/f3 < 1.5 (7) 0.2 < ¦r16¦/f4 < 1.5 wherein fW represents the focal length at a wide-angle end; fi (i = 1, 2, 3 and 4) represents the focal length of the i-th lens group; d14 represents an air space between the third and fourth lens groups; r11 represents the radius of curvature of an object side surface of the positive lens forming the third lens group; r16 represents the radius of curvature of the cemented surfaces of the lenses of the fourth lens group. More preferably, the Z value of the negative lens of the fourth lens group is chosen to satisfy the following condition. (9) Z = (1/r16 - 1/r15)·D/4 > 0.09 wherein r15 represents the radius of curvature of an object side surface of the negative lens forming the fourth lens group facing towards the object side; r16 represents the radius of curvature of the cemented surfaces of the cemented lenses of the fourth lens group; and D represents the diameter of the negative lens of the fourth lens group. Again preferably, the second negative lens of the second lens group counted from the object side is in the form of concave surfaces having its opposite surfaces of an equal radius of curvature. A video camera designed to accomplish the above described object of the present invention comprises at least the zoom lens assembly of the present invention, an imaging element, a signal processing circuit and a viewfinder. According to the present invention, the provision of the first lens group including a negative lens, a positive lens and a positive meniscus lens, the second lens group including a negative meniscus lens, a negative lens and a positive lens, the third lens group having at least one aspherical surface and including a positive lens and a negative lens, and the fourth lens group including a lens having at least one aspherical surface and also including a negative lens and a positive lens, makes it possible to provide a high magnification zoom lens assembly of simplified structure having a zooming ratio of about 10. If the conditions (1) to (7) are satisfied, the high performance zoom lens assembly of simplified structure effective to correct aberrations satisfactorily can be realized. If the condition (9) is additionally satisfied, any possible centering error which would occur when the negative lens of the fourth lens group is subjected to a centering process can advantageously be minimized to make it possible to eventually provide the high performance zoom lens assembly which has been highly precisely processed. The use of the zoom lens assembly according to the present invention makes it possible to realize the compact and light-weight, high magnification video camera capable of providing a high quality image. Thus, the present invention is effective to provide, for example, a high performance zoom lens assembly having a minimized number of, for example, 10, lens elements and also having an F-number of about 1.8, a zooming ratio of about 10 with chromatic aberrations corrected satisfactorily. In addition, if this zoom lens assembly of the present invention is utilized, the compact, light-weight high performance video camera can be realized. BRIEF DESCRIPTION OF THE DRAWINGS This and other objects and features of the present invention will become clear from the following description taken in conjunction with preferred embodiments thereof with reference to the accompanying drawings, in which like parts are designated by like reference numerals and in which: Fig. 1 is a schematic diagram showing an optical system of a zoom lens assembly according to a first embodiment of the present invention; Fig. 2 is a schematic diagram showing the optical system employed in the prior art zoom lens assembly; Figs. 3 to 5 are graphs showing various aberrations exhibited by the zoom lens assembly of Fig. 1 when the zoom lens assembly is set at a wide-angle end, a standard setting and a telephoto end, respectively; Figs. 6 to 8 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a second embodiment of the present invention; Figs. 9 to 11 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a third embodiment of the present invention; Figs. 12 to 14 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a fourth embodiment of the present invention; Figs. 15 to 17 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a fifth embodiment of the present invention; Figs. 18 to 20 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a sixth embodiment of the present invention; Figs. 21 to 23 are graphs similar to Figs. 3 to 5, respectively, exhibited by the zoom lens assembly according to a seventh embodiment of the present invention; and Fig. 24 is a schematic block diagram showing a video camera according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS Referring now to Fig. 1, a zoom lens assembly according to the present invention comprises, in the order from an object side where an object to be photographed or videoed is situated, a first lens group 1, a second lens group 2, a third lens group 3, a fourth lens group 4, a flat plate 5 which is an optical equivalent of a quartz filter and the faceplate of the image device or the like, and an image plane 6. The first lens group has a positive refractive power and also has an image forming function; a second lens group has a negative refractive power and movable along the optical axis of the zoom lens assembly for zooming, i.e., focal length adjustment; a third lens group has a positive refractive power and also has a light condensing function; and a fourth lens group has a positive refractive power and is movable along the optical axis of the zoom lens assembly for focus adjustment. In the successive order from the object side, the first lens group includes cemented lenses and a meniscus lens having a positive refractive power; the second lens group 2 includes a meniscus lens having a negative refractive power and cemented lenses; the third lens group has at least one aspherical surface and includes a positive lens and a negative lens; and the fourth lens group includes a lens having at least one aspherical surface and also including a negative lens and a positive lens which is cemented together with the negative lens. In order to make the zoom lens assembly compact, it is necessary to increase the refractive power of each of the lens groups. The conditions (1), (2), (3) and (4) discussed hereinbefore define the refractive power of each of the lens groups and stipulate respective ranges which give an increased refractive power required to realize the compactness and optimize the lens type of and the surface configuration of each lens group. The condition in which the third lens group has at least one aspherical surface and includes, in the order from the object side, a positive lens having a convex surface oriented towards the object side and a negative lens having a concave surface oriented towards the image forming plate 6 makes it essential to employ two lenses to form the third lens group 3 and also to compensate for various aberrations resulting from the large aperture of about 1.8 in F-number. In fact, the aspherical surface configuration of the third lens group is effective to correct a spherical aberration. The condition in which the fourth lens group 4 includes a negative lens having a concave surface oriented towards the image forming plane and a positive lens having a convex surface oriented towards the object side and cemented together with the negative lens and, yet, has at least one aspherical surface makes it essential to employ a minimized number of, for example, two, lenses to form the fourth lens group 4 and also to compensate for on-axis and off-axis chromatic aberrations and also for a monochromatic off-axis aberration and, particularly, coma. Each of the conditions (1) to (9) will now be discussed in detail. The condition (1) is associated with the refractive power of the first lens group 1. If the ratio f1/fW is smaller than the lower limit, the refractive power of the first lens group 1 will become to large to make it difficult to compensate for the spherical aberration at a setting of long focal length. On the other hand, the ratio f1/fW is greater than the upper limit, the zoom lens assembly as a whole will have an increased length and no compact zoom lens assembly can be realized. The condition (2) is associated with the refractive power of the second lens group 2. Although the zoom lens assembly as a whole can be made compact if the ratio ¦f2¦/fW is smaller than the lower limit, Petzval's sum of the zoom lens assembly as a whole will become large and negative to such an extent that selection of glass material will no longer bring about a correction of field curvature. On the other hand, if the ratio f2/fW is greater than the upper limit, an aberration can easily be corrected, but the zooming system tends to be lengthened making it impossible to provide the compact zoom lens assembly. The condition (3) is associated with the refractive power of the third lens group 3. If the ratio f3/fW is smaller than the lower limit, the refractive power of the third lens group 3 will become excessively large and not only can a back focal distance in which the quartz filter is inserted not be realized, but the correction of the spherical aberration become difficult to achieve. On the other hand, if this ratio is greater than the upper limit, a composite optical system including the first to third lens groups 1 to 3 will become a divergent optical system and, therefore, the lens diameter of the fourth lens group 4 cannot be reduced while Petzval's sum of the entire optical system cannot also be reduced. The condition (4) is associated with the refractive power of the fourth lens group 4. If the ratio f4/fW becomes smaller than the lower limit, the quantity of light at a corner of the image becomes small and the lens size of the first lens group 1 must be increased in order to compensate for the reduction in quantity of light at the corner of the image, making it impossible to realize compact and lightweight features in the zoom lens assembly. On the other hand, if this ratio exceeds beyond the upper limit, aberrations can easily be corrected, but the fourth lens group 4 requires an increased stroke for its movement when the zoom lens assembly is set at a close photo-taking range, not only making it impossible to realize a compact feature in the zoom lens assembly, but also making it difficult to compensate for an unbalance between an off-axis aberration exhibited when the zoom lens assembly is set at the close photo-taking range and when the same is set at a distant photo-taking range. The condition (5) is associated with the air space existing between the third lens group 3 and the fourth lens group 4. When the ratio d14/f4 is greater than the upper limit, the height of off-axis rays of light becomes small to such an extent that selection of a glass material will no longer bring about a correction of lateral chromatic aberration and, at the same time, the stroke of movement of the fourth lens group 4 at the time of photo-taking at a close range will be limited, resulting in the zoom lens assembly incapable of focusing an object at a closest possible distance away from the lens assembly. On the other hand, if this ratio become greater than the upper limit, the zoom lens assembly as a whole cannot be made compact. In addition, when a suitable quantity of light is desired to be ensured around the image plane, the lens size of the fourth lens group cannot be reduced. The condition (6) is associated with the radius of curvature of the object side surface of the positive lens forming a part of the third lens group 3. By introducing an aspherical surface on one or both of the side of the object to be photographed and the side of the image plane and then selecting the shape thereof optimally, various aberrations can satisfactorily be corrected. However, if the ratio r11/f3 is smaller than the lower limit, correction of the spherical aberration will become difficult to achieve, but if the ratio is greater than the upper limit, correction of the coma formed by the off-axis light ray travelling below the principal rays of light becomes difficult to achieve. The condition of Claim 1 is associated with the radius of curvature of the image side surface of the negative lens forming a part of the third lens group 3. By introducing an aspherical surface on one or both of the side of the object to be photographed and the side of the image plane and then selecting the shape thereof optimally, various aberrations can satisfactorily be corrected. However, if the ratio ¦r14¦/f4 is smaller than the lower limit, excessive correction of the spherical aberration may occur, but if this ratio is greater than the upper limit, insufficient correction of the coma formed by the off-axis light ray travelling below the principal rays of light becomes difficult to achieve and no optimization of the shape of the aspherical surface will bring about satisfactory aberration performance. The condition (7) is associated with the radius of curvature of the cemented surfaces of the lenses forming parts of the fourth lens group 4. By introducing an aspherical surface on at least one of the object side surface of a lens having a negative refractive power and forming a part of the fourth lens group 4, the cemented surface and the image side surface of a lens having a positive refractive power forming a part of the fourth lens group 4 and then selecting the shape thereof optimally, a monochromatic aberration can satisfactorily be corrected while on-axis and lateral chromatic aberration are at the same time corrected. However, if the ratio ¦r16¦/f4 is smaller than the lower limit, the angle of incidence of the light on these surfaces will become great making it difficult to correct the coma formed by the off-axis light ray travelling above the principal rays of light, and at the same time, a spherical aberration of F-line will take place excessively. On the other hand, if this ratio is greater than the upper limit, no practical selection of glass material will bring about the on-axis and lateral chromatic aberrations within an acceptable range. The condition (9) is associated with the Z-value of the negative lens forming a part of the fourth lens group 4. If this condition is satisfied, any possible centering error which would occur when the negative lens of the fourth lens group is subjected to a centering process can advantageously be minimized to make it possible to eventually provide the high performance zoom lens assembly which has been highly precisely processed. The condition in which the second negative lens of the lens group 2 counted from the object side has an absolute value of the same radius of curvature is advantageous in that the small size lens which is generally very difficult to differentiate the radius of curvature, such as the second negative lens, will not be inadvertently inserted in the wrong orientation during an assemblage. It is to be noted that, in Fig. 1, the air space exists between the positive and negative meniscus lenses. Specific values of the various parameters of the zoom lens assembly according to the first embodiment of the present invention are tabulated in Table 1. Group Surface r d n ν 1 1 36.009 0.90 1.80518 25.4 2 16.984 4.90 1.58913 61.2 3 -66.650 0.15 4 14.233 2.70 5 41.145 Variable 2 6 44.785 0.60 1.77250 49.6 7 5.156 1.90 8 -6.139 0.60 1.67790 55.5 9 5.845 1.80 1.80518 25.4 10 147.190 Variable 3 11 7.283 2.80 1.60311 60.7 12 -20.099 0.82 13 36.025 0.70 1.80518 25.4 14 10.417 Variable 4 15 8.208 0.70 1.80518 25.4 16 5.690 3.00 1.51633 64.1 17 -15.764 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - wherein: r: Radium of curvature of the surface, d: Lens thickness or Air space between the lenses, n: Refractive index relative to the d-line of each lens, and ν: Abbe number relative to the d-line of each lens. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the first embodiment of the present invention are shown in Figs. 3(a) to 3(c) when the zoom lens assembly is set at the wide-angle end, Figs. 4(a) to 4(c) when the zoom lens assembly is set at the standard setting and Figs. 5(a) to 5(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 3(a), 4(a) and 5(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 3(b), 4(b) and 5(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. The aspherical shape is defined by the following equation. Z = CY 2 1 + 1 - (1 + K ) C 2 Y 2 + D · Y 4 + E · Y 6 + F · Y 8 + G · Y 10 wherein: Z: Distance from top of the aspherical surface at a point on the aspherical surface spaced a height Y from the optical axis, Y: Height from the optical axis, C: Curvature (1/r) of the top of the aspherical surface, K: Conical constant, and D, E, F, G: Coefficient of asphericity. The eleventh, fourteenth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 2. 11th Face 14th Face 17th Face K -5.97319E - 1 3.42145E - 1 -2.15688E + 1 D -1.81760E - 4 1.89782E - 4 -2.35784E - 1 E -7.53020E - 6 -1.01760E - 5 3.68488E - 5 F 2.56976E - 7 3.81949E - 7 -1.84785E - 6 G -6.52307E - 9 -2.26979E - 8 6.62663E - 8 Values of the air spaces which are variable with change in focal length consequent upon zooming are tabulated in Table 3 when the zoom lens assembly is focused at an object at infinity, in Table 4 when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly and in Table 5 when the zoom lens assembly is focused at an object spaced 1 meter away from the front of the zoom lens assembly, respectively. Object at infinity Wide-angle End Standard Set. Telephoto End f 4.344 21.491 42.886 F/NO 1.854 2.215 2.626 d5 0.800 9.418 12.161 d10 13.250 4.632 1.890 d14 4.792 1.162 4.792 d17 2.000 5.630 2.000 Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.343 22.818 42.224 F/NO 1.854 2.252 2.521 d5 0.800 9.654 12.161 d10 13.250 4.396 1.890 d14 4.782 0.921 3.882 d17 2.010 5.871 2.911 Object at 1 meter away Wide-angle End Standard Set. Telephoto End f 4.343 24.260 41.642 F/NO 1.855 2.294 2.523 d5 0.800 9.896 12.161 d10 13.250 4.154 1.890 d14 4.773 0.659 3.056 d17 2.020 6.133 3.736 wherein f and F/NO represent the focal length and the F-number, respectively. In Tables 3 to 5, at the standard setting of the zoom lens assembly, the fourth lens group 4 occupies the position closest to the third lens group 3 regardless of the lens-to-object distance. Specific values of the various parameters of the zoom lens assembly according to a second embodiment of the present invention are tabulated in Table 6. Group Surface r d n ν 1 1 33.906 0.90 1.80518 25.4 2 15.943 5.30 1.67790 55.5 3 -81.746 0.15 4 14.596 1.80 1.67790 55.5 5 21.105 Variable 2 6 33.780 0.60 1.67790 55.5 7 5.425 2.40 8 -7.180 0.60 1.74400 44.9 9 5.255 2.60 1.80518 25.4 10 -213.469 Variable 3 11 7.299 3.00 1.60311 60.7 12 -16.458 1.57 13 27.796 0.70 1.84666 23.9 14 8.032 Variable 4 15 6.950 0.70 1.84666 23.9 16 5.642 2.90 1.51633 64.1 17 -21.772 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 7. 11th Face 12th Face 17th Face K -3.78852E - 1 -2.00148E + 1 -4.32521E + 1 D -2.27610E - 4 -3.01348E - 4 6.52644E - 5 E -1.42803E - 5 3.07697E - 7 5.50900E - 5 F 8.08452E - 7 1.80844E - 7 -4.03897E - 6 G -4.19980E - 8 -2.80572E - 8 1.55222E - 7 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 8. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.343 22.818 42.224 F/NO 1.854 2.252 2.521 d5 0.800 9.654 12.161 d10 13.250 4.396 1.890 d14 4.782 0.921 3.882 d17 2.010 5.871 2.911 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the second embodiment of the present invention are shown in Figs. 6(a) to 6(c) when the zoom lens assembly is set at the wide-angle end, Figs. 7(a) to 7(c) when the zoom lens assembly is set at the standard setting and Figs. 8(a) to 8(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 6(a), 7(a) and 8(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 6(b), 7(b) and 8(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. Specific values of the various parameters of the zoom lens assembly according to a third embodiment of the present invention are tabulated in Table 9. Group Surface r d n ν 1 1 36.597 0.90 1.80518 25.4 2 16.852 4.90 1.58913 61.2 3 -65.769 0.12 4 14.110 2.70 1.60311 60.7 5 41.278 Variable 2 6 41.278 0.60 1.77250 49.6 7 5.056 1.91 8 -6.093 0.80 1.66547 55.2 9 6.093 1.79 1.79927 24.5 10 136.868 Variable 3 11 7.357 2.80 1.60602 57.4 12 -16.959 0.94 13 41.776 0.70 1.80518 25.4 14 9.653 Variable 4 15 7.803 1.00 1.79927 24.5 16 5.400 3.10 1.51450 63.1 17 -16.243 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 10. 11th Face 12th Face 17th Face K -5.32087E - 1 -2.25106E + 1 -1.51435E + 1 D -1.71823E - 4 -2.90632E - 4 3.10551E - 5 E -1.45803E - 5 2.49169E - 6 3.06352E - 5 F 8.86719E - 7 5.30822E - 7 -1.95928E - 6 G -3.13821E - 8 -2.95660E - 8 6.39734E - 8 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 11. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.343 22.929 42.375 F/NO 1.854 2.289 2.534 d5 0.800 9.655 12.167 d10 13.260 4.405 1.893 d14 4.826 0.911 3.940 d17 2.010 5.952 2.896 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the third embodiment of the present invention are shown in Figs. 9(a) to 9(c) when the zoom lens assembly is set at the wide-angle end, Figs. 10(a) to 10(c) when the zoom lens assembly is set at the standard setting and Figs. 11(a) to 11(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 9(a), 10(a) and 11(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 9(b), 10(b) and 11(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. Specific values of the various parameters of the zoom lens assembly according to a fourth embodiment of the present invention are tabulated in Table 12. Group Surface r d n ν 1 1 36.597 0.90 1.80518 25.4 2 16.852 4.90 1.58913 61.2 3 -65.769 0.12 4 14.110 2.70 1.60311 60.7 5 41.278 Variable 2 6 41.278 0.60 1.77250 49.6 7 5.056 1.91 8 -6.093 0.80 1.66547 55.2 9 6.093 1.79 1.79927 24.5 10 136.868 Variable 3 11 7.326 2.80 1.60602 57.4 12 -17.508 0.91 13 44.011 0.70 1.80518 25.5 14 10.288 Variable 4 15 9.401 0.80 1.84666 23.9 16 6.000 2.90 1.60602 57.4 17 -20.386 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 13. 11th Face 12th Face 17th Face K -5.31027E - 1 -9.56058 -4.14909 D -1.26176E - 4 1.13680E - 4 2.68819E - 4 E -5.03169E - 6 -6.44825E - 6 6.51502E - 6 F 2.87530E - 7 4.13744E - 7 -1.06380E - 7 G -9.16376E - 10 -1.72856E - 9 -4.69431E - 10 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 14. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.350 22.572 42.336 F/NO 1.856 2.233 2.529 d5 0.800 9.655 12.170 d10 13.260 4.405 1.890 d14 5.126 1.240 4.226 d17 2.010 5.895 2.910 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the fourth embodiment of the present invention are shown in Figs. 12(a) to 12(c) when the zoom lens assembly is set at the wide-angle end, Figs. 13(a) to 13(c) when the zoom lens assembly is set at the standard setting and Figs. 14(a) to 14(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 12(a), 13(a) and 14(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 12(b), 13(b) and 14(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. Specific values of the various parameters of the zoom lens assembly according to a fifth embodiment of the present invention are tabulated in Table 15. Group Surface r d n ν 1 1 36.597 0.90 1.80518 25.4 2 16.852 4.90 1.58913 61.2 3 -65.769 0.12 4 14.110 2.70 1.60311 60.7 5 41.278 Variable 2 6 41.278 0.60 1.77250 49.6 7 5.056 1.91 8 -6.093 0.80 1.66547 55.2 9 6.093 1.79 1.79927 24.5 10 136.868 Variable 3 11 7.474 2.90 1.60602 57.4 12 -16.980 1.07 13 46.609 0.7 1.80518 25.5 14 10.250 Variable 4 15 9.401 0.80 1.84666 23.9 16 6.120 2.90 1.60602 57.4 17 -21.214 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 16. 11th Face 12th Face 17th Face K -7.52155E - 1 -8.50418 -7.13905E - 1 D -7.05771E - 5 9.32650E - 5 3.15765E - 4 E -5.45719E - 6 -7.31403E - 6 4.23078E - 6 F 3.21874E - 7 4.53663E - 7 5.40588E - 8 G -2.07794E - 9 -5.47877E - 9 -5.12863E - 9 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 17. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.452 22.046 42.128 F/NO 1.853 2.069 2.324 d5 0.800 9.655 12.167 d10 13.260 4.405 1.893 d14 5.278 1.556 3.905 d17 2.010 5.261 2.912 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the fifth embodiment of the present invention are shown in Figs. 15(a) to 15(c) when the zoom lens assembly is set at the wide-angle end, Figs. 16(a) to 16(c) when the zoom lens assembly is set at the standard setting and Figs. 17(a) to 17(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 15(a), 16(a) and 17(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 15(b), 16(b) and 17(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. Specific values of the various parameters of the zoom lens assembly according to a sixth embodiment of the present invention are tabulated in Table 18. Group Surface r d n ν 1 1 41.099 0.90 1.80518 25.4 2 18.520 5.10 1.58913 61.2 3 -62.450 0.12 4 14.908 2.70 1.60311 60.7 5 38.640 Variable 2 6 38.640 0.60 1.77250 49.6 7 5.694 2.13 8 -6.668 0.80 1.66547 55.2 9 6.668 1.90 1.79927 24.5 10 82.608 Variable 3 11 7.437 3.20 1.60602 57.4 12 -16.418 1.29 13 34.280 0.6 1.80518 25.5 14 8.417 Variable 4 15 9.268 0.80 1.80518 25.5 16 6.116 2.90 1.60602 57.4 17 -26.443 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 19. 11th Face 12th Face 17th Face K -8.97657E - 1 -4.56501 8.31235 D -9.38070E - 5 1.07830E - 4 2.75578E - 4 E -1.90203E - 6 -5.38185E - 6 7.19498E - 6 F 1.40979E - 7 2.75671E - 7 -3.28682E - 7 G -3.98412E - 9 -7.14998E - 9 1.03774E - 8 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 20. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.766 25.545 46.756 F/NO 1.854 2.270 2.714 d5 0.800 10.613 13.356 d10 14.536 4.723 1.980 d14 5.708 1.229 4.613 d17 2.011 5.490 3.106 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the sixth embodiment of the present invention are shown in Figs. 18(a) to 18(c) when the zoom lens assembly is set at the wide-angle end, Figs. 19(a) to 19(c) when the zoom lens assembly is set at the standard setting and Figs. 20(a) to 20(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 18(a), 19(a) and 20(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 18(b), 19(b) and 20(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. Specific values of the various parameters of the zoom lens assembly according to a seventh embodiment of the present invention are tabulated in Table 21. Group Surface r d n ν 1 1 41.099 0.90 1.80518 25.4 2 18.520 5.10 1.58913 61.2 3 -62.450 0.12 4 14.908 2.70 1.60311 60.7 5 38.640 Variable 2 6 38.640 0.60 1.77250 49.6 7 5.694 2.13 8 -6.668 0.80 1.66547 55.2 9 6.668 1.90 1.79927 24.5 10 82.608 Variable 3 11 7.598 3.20 1.60602 57.4 12 -16.600 0.80 13 50.311 0.6 1.75520 27.5 14 9.535 Variable 4 15 9.955 0.80 1.80518 25.5 16 6.116 2.90 1.60602 57.4 17 -24.743 Variable 5 18 ∞ 4.00 1.51633 64.1 19 ∞ - The eleventh, twelfth and seventeenth surface are aspherical surfaces having respective coefficients of asphericity as tabulated in Table 22. 11th Face 12th Face 17th Face K -8.55168E - 1 -6.22739 9.19465 D -7.33785E - 5 8.97694E - 5 2.73081E - 4 E -2.53188E - 6 -4.46316E - 6 4.81603E - 6 F 1.86967E - 7 2.43688E - 7 -1.25534E - 7 G -2.84707E - 9 -3.90964E - 9 4.11777E - 9 Values of the air spaces which are variable with change in focal length consequent upon zooming and which are exhibited when the zoom lens assembly is focused at an object spaced 2 meters away from the front of the zoom lens assembly are tabulated in Table 23. Object at 2 meters away Wide-angle End Standard Set. Telephoto End f 4.766 25.168 46.671 F/NO 1.853 2.233 2.707 d5 0.800 9.655 12.167 d10 13.260 4.405 1.893 d14 6.208 1.798 5.102 d17 2.012 6.422 3.117 wherein f and F/NO represent the focal length and the F-number, respectively. Spherical aberration, astigmatism and field distortion all exhibited by the zoom lens assembly according to the seventh embodiment of the present invention are shown in Figs. 21(a) to 21(c) when the zoom lens assembly is set at the wide-angle end, Figs. 22(a) to 22(c) when the zoom lens assembly is set at the standard setting and Figs. 23(a) to 23(c) when the zoom lens assembly is set at the telephoto end, respectively. It is to be noted that, in each of Figs. 21(a), 22(a) and 23(a), solid lines, dotted lines and broken lines represent respective values relative to the d-line, the F-line and the C-line and that in each of Figs. 21(b), 22(b) and 23(b) solid lines and dotted lines represents aberrations at meridional and sagittal image planes, respectively. The diameter and the Z-value of the negative lens forming a part of the fourth lens group 4 employed in any one of the first to fourth embodiments of the present invention are tabulated in Table 24. This Table 24 makes it clear that the Z-value in any one of the fourth to seventh embodiments of the present invention is greater than 0.09 and, therefore, the possible centering error can be minimized during the centering process. Embodiment D Z-value 4 6.8 0.103 5 6.9 0.098 6 7.2 0.100 7 7.2 0.113 A video camera according to the present invention is schematically shown in Fig. 24. As shown therein, the video camera comprises at least the high magnification zoom lens assembly 11 of any one of the previously discussed embodiments, an imaging element 12, a signal processing circuit 13 and a viewfinder 14 and, with these component parts, a compact and lightweight, high performance video camera can be realized. Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. For example, although the positive lens forming a part of the third lens group 3 has been described as having an aspherical surface, the present invention can be equally applied to the use of a negative lens having an aspherical surface or the use of both lenses having an aspherical surface. Also, although of the cemented lenses forming parts of the fourth lens group 4 the positive lens has been described as having an aspherical surface, the present invention can be equally applied to the use of the negative lens having an aspherical surface or the use of aspherical lenses both having cemented aspherical surfaces. Accordingly, such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.

Claims: A zoom lens assembly (11) which comprises, in the successive order from the object side; a first lens group (1) having a positive refractive power and fixed relative to an image plane (6); a second lens group (2) having a negative refractive power for effecting a variation of image magnification by moving along an optical axis of the zoom lens assembly (11); a third lens group (3) having a positive refractive power, said third lens group (3) being fixed relative to the image plane (6); and a fourth lens group (4) having a positive refractive power and movable along the optical axis to focus and to adjust focus when a variation in image magnification is affected by a movement of said second group (2); wherein the first lens group (1) includes a negative lens, a positive lens and a positive meniscus lens in the successive order from the object side; wherein the second lens group (2) includes a negative meniscus lens, a negative lens and a positive lens in the successive order from the object side; wherein the third lens group (3) has at least one aspherical face and includes a positive lens having a convex surface oriented towards the object side; and wherein the fourth lens group (4) includes a lens having at least one aspherical surface and also including a negative lens and a positive lens in the successive order from the object side, said negative and positive lenses of said fourth lens group being (4) cemented together; characterized in that the third lens group (3) includes additionally to the positive lens, in the successive order from the object side, a negative lens having a concave surface oriented towards the image plane and that 0.3 < ¦r14¦/f4 < 2.0, wherein r14 represents the radius of curvature of the image side surface of the negative lens of the third lens group (3) and f4 represents the focal length of the 4th lens group. The zoom lens assembly (11) as claimed in Claim 1, wherein the fourth lens group (4) includes, in the successive order from the object side, a negative lens having a concave surface oriented towards the image plane (6) and a positive lens having a convex surface oriented towards the object side, said negative and positive lenses being cemented together and has at least one aspherical surface. The zoom lens assembly (11) as claimed in Claim 1, wherein the zoom lens assembly (11) satisfies the following conditions: (1) 3.0 < f1/fW < 8.0 (2) 0.5 < ¦f2¦/fW < 1.6 (3) 2.0 < f3/fW < 7.0 (4) 2.0 < f4/fW < 5.0 (5) 0.02 < d14/f4 <1.0 (6) 0.3 < r11/f3 < 1.5 (7) 0.2 < ¦r16¦/f4 < 1.5 wherein fW represents the focal length at a wide-angle end; fi (i = 1, 2, 3 and 4) represents the focal length of the i-th lens group (1, 2, 3, 4); d14 represents an air space between the third (3) and fourth lens groups (4); r11 represents the radius of curvature of an object side surface of the positive lens forming the third lens group (3); r16 represents the radius of curvature of the cemented surfaces of the lenses of the fourth lens group (4). The zoom lens assembly (11) as claimed in Claim 1, wherein the negative lens of the fourth lens group (4) has a Z-value chosen to satisfy the following condition. (9) Z = (1/r16- -1/r15)·D/4 > 0.09 wherein r15 represents the radius of curvature of an object side surface of the negative lens forming the fourth lens group (4); r16 represents the radius of curvature of the cemented surfaces of the cemented lenses of the fourth lens group (4); and D represents the diameter of the negative lens of the fourth lens group (4). The zoom lens assembly (11) as claimed in Claim 1, wherein the second negative lens of the second lens group (2) counted from the object side is in the form of concave surfaces having its opposite surfaces of an equal radius of curvature. A video camera which comprises at least the zoom lens assembly (11) as defined in Claim 1, an imaging element (12), a signal processing circuit (13) and a viewfinder (14).

Inventors: II HISAYUKI, NAKAJIMA YASUO, OKAYAMA HIROAKI, ONO SHUSUKE, II, HISAYUKI, NAKAJIMA, YASUO, OKAYAMA, HIROAKI, ONO, SHUSUKE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G02B15
IPC codes: G02B15