GB2301456A - Three group zoom lens - Google Patents

Description

1 2301456 ZOOM LEiS The present invention relates to a conpact zoom lens

system having a high zoom ratio.

Recently, so called "compact" cameras tend to have zoom features in addition to having automatic features and being compact. Historically, zoom lenses have been widely used for single lens reflex cameras, and various types of zoom lenses for such applications have been proposed. However, zoom lenses designed for single-lens reflex cameras are not suitable for compact camera applications because such zoom lenses have a long back focus distance and are not sufficiently compact.

For compact cameras, two types of zoom lenses have been proposed. The first type is composed of two lens groups and typically has an approximately 1.5 times zoom ratio. However, for a zoom ratio greater than 2.0, this first type can not practically be made compact.

The second type is composed of three lens groups and typically has an approximately 2.5 times zoom ratio. U. S. patents No. 4,978,204; 5,002, 373; and 5,033,832 have proposed the second type. However, the zoom ratio of this second type is limited to an approximately 2.6 times, and this zoom ratio is not sufficient for compact camera applications.

For example, U. S. patents No. 4,970,204 and 5,002,373 proposed zoom lenses of the second type having an approximately 1 1 4D 1 2.6 times zoom ratio and composed of eleven elements. U. S. patent 5,033, 832 proposed zoom lenses of the second type having an approximately 2.7 times zoom ratio and cc-,,,posed of twelve (12) elements. The zoom lenses proposed in the 1832 paten- widen the viewing angle at an wide angle position, but its 2.7 times zoom ratio is still insufficient. For compact cameras, the zoom ratio of at least 3.5 times is desired.

The present invention overcomes the problems and disadvantages of the prior art by providing a zoom lens system of three lens groups which is compact and has sufficiently high magnification, i.e., approximately 3.5 times zoom ratio, while delivering a good optical performance.

To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the zoom lens system of the present invention comprises a first lens group having a positive refractive power, a second lens group having a positive refractive power and spaced from the first lens group at a first distance, and a third lens group having a negative refractive power and spaced from the second lens group at a second distance, the first and second distances being variable during zooming, wherein 3.0 < fT/fwj and LT/fT < "C) where fT: focal length of the zoom lens system at a 2 telephoto position, : focal length of the zoom lens system at a wide angle position, : distance from the first surface of the toom lens f system to the image plane at a telephoto position.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objets and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and together with the description, serve to explain the principles of the invention.

Fig. 1 is a sectional view of a zoom lens at (a) wide angle, (b) middle and (c) telephoto positions according to a first preferred embodiment of the present invention.

Fig. 2 shows the extent of various aberrations associated with the zoom lens at (a) wide angle, (b) middle and (c) telephoto positions, according to the first preferred embodiment of the present invention.

Fig. 3 is a sectional view of a zoom lens at (a) wide angle, (b) middle and (c) telephoto positions according to a second preferred embodiment of the present invention.

2) Fig. 4 shows the extent of various aberrations associated with the zoom lens at (a) wide angle, (b) middle and (c) telephoto positions, according to the second preferred embodiment of the present invention.

Fig. 5 is a sectional view of a zoom lens at (a) wide angle, (b) middle and (c) telephoto positions according to a third preferred embodiment of the present invention.

Fig. 6 shows the extent.of various aberrations associated with the zoom lens at (a) wide angle, (b) middle and (c) telephoto positions, according to the third preferred embodiment of the present invention.

Reference will now be made in detail to first, second and third preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings in reference to Figs. 1, 3, and 5, respectively. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

To facilitate the understanding of the structure and operation of the zoom lens system of the present invention, as embodied herein, the description of the zoom lens system according to the above three embodiments of the present invention is first collectively made in reference to paragraphs I through IX.

I. Referring to Figs. 1, 3, and 5, the zoom lens system, as embodied herein, includes a first lens group I, a second lens 4 0 group II, and a third lens group III spaced from one another and arranged in sequence, in the respective order from, the object side. Second lens group II includes a first lens subgroup lIa and a second lens subgroup IIb spaced from one another at a given distance, and arranged in sequence in the respective order form the object side. First and second lens groups I and II, as embodied herein, preferably have a positive refractive power and third lens group III has a negative refractive power.

In the zoom lens system, as embodied herein, preferably the distance between first and second lens groups I and II, and the distance between second and third lens groups II and III are varied during zooming. To obtain th desired high zoom ratio, 1 the zoom lens system, as embodied herein, preferably satisfies a relation:

3-0 < fTlfW --------------- (1) where fT is the focal length of the zoon, lens system at a telephoto position and fw is the focal length of the zoom lens system at a wide angle position.

II. To obtain compactness, the zoom lens.system, as embodied herein, preferably satisfies relations:

LT/fT < 10 -------- (2) 3.5 < MIIIT < 5.5 ---------- (3) where LT is the distance from the first surface of the zoom lens system to the image plane at a telephoto position, and nIIIT is a lateral magnification ratio of third lens group III at a telephoto position. The first surface refers to the surface of 0.0 0 0 4 A 1 1 the zoom lens facing the object and the image plane refers to the camera film or the focusing side orposite the object.

III. The zoom lens system, as embodied herein, preferably satisfies following relations: 0-18 < f"IIT/fT < 0.28 ---- (4) -0.20 < fIII/fT < -010 --- (5) where f,'IIT is a combined focal length of first and second lens groups I and II at a telephoto position, and MI is the focal length of third lens group III of the zoom lens system.

IV. First lens group I of the zoom lens system, as embodied herein, preferably includes at least one element of negative lens and positive lens, and satisfies relations:

< vI - L)I ------------- (7) P 'J where fI. is the focal length of the negative lens of first lens group 1; vI, is an average of the ABBE number of the positive lens of first lens group I; and uI. is an average of the ABBE number of the negative lens of first lens group I. Hereinafter, the negative lens refers to a lens having a negative refractive power and positive lens a lens having a positive refractive power.

V. In second lens group II of the zoom lens system, as embodied herein, first lens subgroup IIa preferably includes at least one element of negative lens and positive lens. Second lens subgroup IIb preferably includes at least one element of negative lens and positive lens. Second lens group II preferably 6 satisfies relations:

< vIIbp - vIIbN - - - - - - - - - (8) where vIIbp is an average of the ABBE number of the positive lens of second subgroup Ilb and ulIb,, is an average of' the ABBE number of the negative lens of second subgroup IIb of second lens group II.

VI. Third lens group III of the zoom lens system, as embodied herein, preferably includes two elements of negative lens and one element of positive lens, and satisfies 0-15 < f1IIP/fT < 0.28 ----- (9) where fIIIp is the focal length of the positive lens of third lens group III.

VII. The zoom lens system, as embodied herein, preferably satisfies relations:

A D1,II/fT -A D11,111/fT ------- JA D /f < 0 10 ---------- (11) 1, 11 T Where DI'l, is the change in the distance between first and second lens groups I and II when the position of the zoom lens system changes from a, telephoto position to a wide angle position; and DI1,111 is the change in the distance between second and third lens groups II and III whdn the position of the zoom lens system changes from the telephbto position to the wide angle position.

VIII. The zoom lens system, as embodied herein, preferably satisfies relations:

fI/fT "" 0.55 ------------------- (12) 1 1 - - - - - - - (13) lfl"l"W/f"""TI > 'S; fl111T < 0 where fi: focal length of first lens group I we- c- o^ ek, 4A, v- Ck fu,iii.: combined focal length of f4:r-e and -s-e-e lens groups I and II at a wide angle posi:tion <,e- C.0 A Ck f11'111T: combined focal length of firs and GeaeR lens groups I IX. The surface of the present invention, as spherical.

The operation of the zoom lens system of the present invention, as embodied in the first, second and third embodiments, is described collectively in reference to paragraphs I through IX above.

Paragraph 1 set.s forth a basic condition for the construction of the zoom lens system and more particularly the disposition of the refractive power among the lens groups within the zoom lens system, to obtain one of the primary features of the present invention, i.e., a large zoom ratio.

Paragraph II relates to obtaining another feature of the present invention, i.e., compactness. The zoom lens system of the present invention, as embodied herein, includes three lens groups I, II, and III in which the total length of the zoom lens system is normally maximized,,; hen the system is at a telephoto position. However, to obtain a large zoom ratio while simultaneously being compact, the total length of the zoom lens system, as embodied herein, is preferably made smaller than the and II at a telephoto position each lens in the zoom lens system of embodied herein, is preferably 9 focal length of the zoom lens system at a telephoto position, by satisfying the condition set forth in relation (3).

It is well established that f = fjmjjmjjj Where f: the focal length of the zoom lens system fj: focal length of first lens group I of the zoom lens system mjj: lateral magnification ratio of second lens group II m,,,: lateral magnification ratio of third lens group III. Accordingly, to enlarge focal length f of the zoom lens system at a telephoto position, all or any of the above three elements fl, mjjj and mjjj should be enlarged.

However, the enlargement of f, is not desired because it decreases the refractive power of first lens group I, and makes it difficult to make the zoom lens system compact. Further, although the enlargement of mii helps make the zoom lens system compact, it makes it difficult to compensate for aberrations associated with third lens group III because first and second lens groups I and II have a strong positive refractive power.

Therefore, according to the embodiments of the present invention, to make the zoom lens system compact, focal length f of the zoom lens system is enlarged by setting mjjj, i.e., lateral magnification ratio of third lens group III, at a telephoto position to a value which falls within the range set forth in relation (3). If the value of in,,, falls below the lower limit of the range set forth in relation (3), a large zoom ratio cannot be obtained. On the other hand, if it exceeds the I 9 4 0 upper limit, the refractive power of third lens group III becomes excessive, thus making it difficult t,c ccrmpensa- te for aberrations and creating a problem during lens assembly because it excessively increases lens sensitivity.

Paragraph III relates to obtaining a large zoom ratio and compactness in greater details. Relation (4) represents a combined refractive power of first and second lens groups I and II of the zoom lens system at a telephoto position, and if the combined power falls below the lower limit of the range set forth in relation (4), the refractive power of first lens group I and second lens group II become excessive, thus making it difficult to compensate for aberrations the negative power of third lens group III. On the other hand, if it exceeds the upper limit, although it may help compensate for aberrations in third lens group III, it would make it difficult to make the system compact.

Relation (5) sets forth a range of refractive power of third lens group III. The distance between second and third lens groups II and III is determined by the condition set forth in relation (4) as well'as relation (5). In the condition set forth in relation (5), if the focal length of third lens group III falls below the lower limit of the range set forth therein, it increases the distance between second and third lens groups II and III, making it difficult to make the zoom lens system compact. If the focal length exceeds the upper limit, it degrades the performance because it increases aberrations.

Paragraph IV sets forth the condition for compensating for generic aberrations and chromatic aberrations for first lens group I of the zoom lens systen. More specifically, to minimize variations in chromatic aberrations in the zoom lens which occur during zooming and obtain high performance, chromatic aberrations associated with each lens group of the zoom lens sy'st-em are -eliminated by satisfying the above condition.

Although aberrations in first lens group I are compensated for by having at least one element of negative lens and positive lens in first lens group I, if the referenced value in relation (6) exceeds the upper limit or falls below the lower limit of the range set forth in relation (6), the compensation for spherical and COPIA aberrations become difficult. Relation (7) sets forth a condition necessary to eliminate chromatic aberrations associated with first lens group I. According to the embodiments of the present invention, to compensate for aberrations and eliminate chromatic aberrations, the refractive power of the positive and negative lens in first lens group is set to a small value, and a material having a large ABBE number is used in the positive lens of first lens group I, as set forth in relation (7).

Further, if first lens group I has at least one element of positive refractive lens using a material with an ABBE number of greater than seventy five (75), it is possible to use a material having a high refractive power in tII-e negative lens, yet satisfying relation (7) and compensating for chromatic and other aberrations with a small lens construction.

Par?graph V relates to the construction of the lens of 11 0 0 a 5 0 ' ' 0 second lens group II. As described above, second lens group II of the zoom lens systen, as embodied herein, includes first subgroup IIa having a negative refractive power and second subgroup IIb having a positive refractive power. Although each lens group eliminates chromatic aberrations and com'pensates for aberrations by having positive and negative lens therein, the elimination of chromatic aberrations is more prominently obtained by second subgroup IIb having a strong positive refractive power, satisfying the condition set forth in relation (8).

Further, in second lens group II, if at least one element of positive lens of second lens subgroup IIb uses a material with a ABBE member of greater than 75, it is possible to use a material having a high refractive power in the negative lens while satisfying relation (8), and yet compensate for chromatic and other aberrations with a small lens construction.

Paragraph VI relates to the construction of the lens of third lens group III of the zoom lens system. Although third lens group III as a whole has a strong negative refractive power, the negative lens alone can not eliminate chromatic aberrations or compensates for Petzvalls sums of the image plane.

Accordingly, third lens group III includes an element of positive lens in addition to two elements of negative lens. Further, to eliminate chromatic aberrations and compensate for Petzval's sums of the refractive power of the positive lens of third lens group III -Js set to a value which falls within the range set forth in relation (9). If the referenced value in 120 & 0 relation (9) exceeds the upper limit or falls below the lower limit of the range set forth in relation (9), the refractive power of the negative lens becomes too large or too small, making it difficult to compensate for aberrations.

Paragraph VII relates to the movements of each lens group in the zoom lens system during zooming. In the zoom lens system, as embodied herein, although it is fundamental to move each of the first, second and third lens groups individually during zooming, even more compact and less expensive zoom lens systems are obtained by satisfying relations (10) and (11).

For example, relation.(10) relates to moving the first and third lens groups collectively during zooming, and this helps make the barrel construction of the lens simpler and less expensive. If relation (10) is not satisfied, the barrel construction or the zoom lens system has to be such that the first through third lens groups in the zoom lens system are moved individually, and this would cause the number of elements in the zoom lens system and the cost of assembly increase, thus increasing the cost of the system.

Relation (11) relates to making the system nore compact by restricting the extent of the change in the distance between the lens groups during zooming. When the zoom ratio is greater than three (3), although in general the extent of the change in the distance between the lens groups during zooming from a wide angle position to a telephoto position can easily amount to approximately 0.15, in accordance with the embodiment of the 11 present invention, the extent of the change is preferably restricted to the range set forth in relation (11) to obt-ai compactness in the zoom lens systems.

Referring to paragraph VIII, in the zoom lens sy.sten, as embodied herein, the focal-length of first lens group I of a positive refractive power is preferably restricted to a value which falls within the range set forth in relation (12), to make the system compact. Further, the combined focal length of second lens group II of a positive refractive power and third lens group III of a negative refractive power is preferably restricted to a value which falls within the range set forth in relation (13), to reduce the total length of the system at a telephoto position.

Relation (13) sets the combined refractive power of second and third groups II and III at a wide angle position to a small value. In other words, at a telephoto position, second and third lens groups II and III having a combined large negative power are disposed behind first lens group I having a strong positive power which satisfies relation (12), viewing from the object. Such disposition of the lens groups helps obtain compactness. In other words, if the referenced value falls Eorth in relations (12) and (13), it is outside the range set f difficult to obtain both compactness and a large zoom ratio simultaneously.

Paragraph IX relates to constructing the above described zoom lens having a high zoo,-,i ratio v-1.th a low cost spherical lens. Although a progress has been made in technique of making U aspheric surface lenses, such aspheric surface lenses are still too expensive. Therefore, for low cost systems, it is advantageous to use spherical lenses instead.

Employing the principles and concepts described above, with presentinvention, it is possible to obtain a compact zoom lens having a high zoom ratio and performance, but yet using low cost spherical lens.

More specifically, the zoom lens system in accordance with each of the first, second and third embodiments of the present invention is discussed individually below. Fig. 1 refers to the zoom lens system according to the first embodiment of the present invention, Fig. 2 shows the extent of various aberrations associated with the zoom lens system 'according to the first embodiment at various zoom lens system positions, and self explanatory. Referring to Fig. 1, the zoom lens embodied herein, preferably includes an aperture stop second and third lens groups II and III and adjacent subgroup IIb of second lens group II.

should be system, as "All between second lens In general, aperture stop A is preferably disposed in the iddl location of the zoom lens system, i.e., in the middle of AIL k_ second lens group II. However, such disposition of aperture stop A necessitates the split of second lens group II into two (2) parts, making the assembly more complicated and amenable to errors and thus making it difficult to obtain a high performance system. Therefore, to overcome these problems in functions and assembly, and to obtain a low cost system, the zoom lens system, as embodied herein, preferably includes aperture stop A between Is 1 0 second and third lens groups II and III, and avoids the splitting of second lens group II. A set of exemplary para-meter values for the zoom lens system of, embodied herein, is provided in reference to Table 'l.' TABLE 1 f wide anqle nedian analg telephoto anale f 39.5 80.0 136.9 Fno 1:3.8 1:6.7 1:10.5 CO 28.90 14.811 8.90 (W= half view angle) Curvature Thickness Refractive Dispersion radius or distance index coefficient rl -36.452 r2 -65.659 di 1.500 nl 1.84666 V1 23.83 r2 94.014 d2 0.150 r4 37078.444 d3 2.400 n2 1.49700 u2 81.61 r5 47.876 d4 0.150 r6 -51.426 d5 3.900 n3 1.49700 U3 81.61 r7 -25.378 d6 1 r8 15.454 d7 1.000 n 4 1.77250 4 49.62 r9 -61.544 d8 3.860 n5 1.72825 v5 28.32 r10 85.933 dg 7.890 ril -11.816 d10 4.250 n6 1. 118749 v 6 70.44 r12 -21.172 dil 1.200 n7 1.84666 v7 23.83 r13 74.806 d12 0.150 r14 -26.927 d13 2.650 nS 1.49700 us 81.61 r15 -174.349 d14 2 r16 -20.267 d15 3.290 ng 1.80518 U9 25.46 r17 -28.027 d16 0.150 ris 74.906 d17 1.200 n10 1.77250 V10 49. 62 rig -13.028 dia 4.310 r20 -84.078 dig 1.500 nil 1.77250 V11 49.62 d20 3 wide anqle median anale telenhoto anale 1 d6 3.020 10.069 13.470 2 d14 13.824 6.775 3.374 3 d20 8.492 32.25 64.928 d20 refers to back focus d-istance fb/ i.e., the distance between the iinage plane and the surface facing the image plane of thLrd lipns group III.

16 The values of the relations (1)-(13) are (1) fT/fW: 3.466 (2) LT/fT 0.886 (3) mIIIT 0.224 (4) fIII1T/fT: -0.139 (5) fIII/fT -0.724 (6) f,N/fT 57.78 (7) VIP - UIN: 4.474 (8) vIIbp - vIIbN: 52.2 (9) fIIIP/fT: 0.206 (10) A D1,1I/fT -A DII,111/fT (11) JA DI,1I/fTI: 0.076 (12) fl/fT 0.464 (13) 1f11'n'W/f11'111T1: 39.7 : 0. 07 6 1 0 conditions set forth in the above as follows:

f Fig. 3 refers to the zoom lens system according to the second embodiment of the present invention. Fig. 4 shows the extent of various aberrations associated with the zoom lens system according to the second embodiment at various zoom lens system positions, which figure should be self explanatory.

Referring to Fig. 3, the zoom lens system, as embodied herein, preferably includes aperture stop A between first and second lens subgroups IIa and IIb of second group 1I.

TABLE 2 wide anc[le median anale telephoto anqle f 39.5 80.0 130.0 Fno 1:3.9 1:6.7 1:10.0 W 28.20 14.60 9.211 Curvature Thickness Refractive Dispersion radius or distance index coefficient ri -45.472 r2 -105.785 dl 1.500 ni 1.84666 V1 23.83 r3 85.583 d2 0.150 r4 -133.005 d3 2.600 n2 1.49700 V2 81.61 r5 41.913 d4 0.150 r6 -64.302 dS 3.700 n3 1.49700 u3 81.61 1 -L- r7 -25.216 d6 1 rs 14.911 d7 1.000 n4 1.77250 1) n 49.62 rg -74.331 dB 3.000 nS 1.69895 us 30.05 r10 40.637 d9 9.710 rll -29.525 d10 2.650 n6 1.48749 v6 70.44 r12 83.270 dil 0.150 n7 1.48749 u7 70.44 r13 -11.927 d12 4.250 r14 -19.730 d13 1.200 ns 1.84666 us f23.83 r15 -47.721 d14 2 r16 -18.417 d15 3.110 ng 1.80518 U9 25.46 r17 -25.781 d16 0.150 r18 69.200 d17 1.200 n10 1.64000 U10 60.15 r19 -12.485 diS 4.950 r20 -71.822 d19 1.500 n11 1.77250 Ull 49.62 d20 3 wide anale median anale teleiDhoto anc[le 1 d6 3.067 9.090 11.836 2 d14 9.769 3.746 1.000 3 d20 8.5 30.54 56.995 The values of the conditions set forth in the above relations (1)-(13) are as follows:

(1) f f 3 291 (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) TI W LT/fT 0.852 TnI,IT 0.220 fIIIIT/fT: -0.128 fI1I/fT -0.733 f,N/fT 57.78 uIp - vIl: 4.550 uIIbp - vIIbN: 41.61 fIIIP/fT: 0.274 A DIpII/fT -A DI1,111/fT JA D, II/fT 1: 0. 0 6 7 fI/fT: 0.403 1 f rl.l"W / f 11.111T 1: 4 - 9 6 : 0. 067 Fig. 5 refers to'the zoom lens system according to the third embodiment of the present invention. Fig. 6 shows the extent of various aberrations associated with the zoom lens system according to the third embodiment at various zoom lens system positions, and should be self explanatory. The zoom lens system, as embodied herein, preferably includes aperture stop A between first and second lens subgroups IIa and Ilb of second group II.

19 1 TABLE 3 wide' ahale redian ancle telenhoto anale f 39.5 80.0 136.0 F 1:4.0 1:6.9 1:10.8 no 28.9 14.8 8.90 Curvature Thickness Refractive Dispersion rad i us or_distance index coefficient rl -25.509 r2 -49.004 di 1.500 nl 1.84666 V1 23.83 r3 -64.874 d2 0.150 r4 -24.980 d3 3.600 n2 1.49700 u2 81.61 r5 29.518 d4 0.150 r6 -116.064 d5 3.700 n3 1.49700 u3 81.61 r7 -29.790 d6 1 r8 12.022 d7 1.000 n4 1.77250 v4 49.62 r9 -176.144 dB 3.000 nS 1.74077 v 5 27.76 r10 47.826 d9 9.750 rll -80.926 dio 2.650 n6 1.49700 t) 6 81.61 r12 44.171 dii 0.150 n7 1.51728 u7 69.68 r13 -10.227 d12 4.250 r14 -16.557 d13 1.200 n8 1.84666 U8 23.83 riS -44.973 d14 2 r16 -16.780 d15 3.210 n9 1.B0518 U9 25.46 r17 23.230 d16 0.150 r18 93.346 d17 1.200 n10 1.77250 V10 49.62 rig -11.412 dia 4.900 r20 -43.980 dig 1.500 nil 1.77250 V11 49.62 d20 3 wide anale nedian angle telephoto an-.lle 1 d.6 3.808 9.423 12.203 2 d14 9.395 3.780 1.000 3 d20 8.502 30.074 59.006 T W LT/fT 0.840 MIIIT 0.201 fIIIIT/fT: -0.115 fIII/fT -0.476 fIN/fT 57.78 t)IP - VIN: 4.940 vIIbp - vIIbt;: 51.82 fIIIP/fT: 0.233 A DI II/fT -A D I1,1II/fT 0.062 JA D1 II/fTI: 0. 0 6 2 f,/f T': 0.350 The values of the conditions set forth in the above relations (1)(13) are as follows:

(1) f /f: 3. 4 3 3 (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 19 (13) ifti.iitw/fii.iit.,1: 3.3 With the present invention, a compact-- zoom lens system having a high magnification (f-,/fw) ratio of approximately 3.5 times and a telephoto ratio (LT/fT) of under 0.9 at a.telephoto position is obtained. Further, the zoom lens system of the present invention uses low cost spherical lenses, instead of more expensive aspheric surface lenses, without degrading the optical performance of the system.

Other embodiments of the inven'tion will be apparent to the skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specif-Lcation and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

2.o a 0 4k 0

Claims (1)

1 A zoom lens system, Comcrising:

first lens group. having a positive refractive power; second lens group having a positive refractive power and spaced from said first lens group at a first distance; and a tird lens group having a negative refractivepower and spaced from said second lens group at a second distance, said first and second distances being variable during zooming, wherein fl/fl < 0.55; f;F.M > 5, firmc- < C; and T 1 where ft: focal length cf said first lens group, f combined fccal length of said first and second lens groups at a wide angle position, and f II.InT: combined fcc-=! 1=n(th of said first and second lens grouns at a telephoto position.

The zoom lens syszem of claim 1, wherein 3A < LT/ fT where f T:

3.

f.r/fw; and < 1.0 focal length of the zoom lens system at a telephoto posit-icn, and fw: focal length of the zoom lens systen at a angle pos-Jt-icn.

The zoom lens cf claim 1, wherein said first and second and third lens cIroups include a spherical lens.

3-