DE8916169U1 - Varifocal lens for one camera - Google Patents

Description

G 89 16 169.6 61 770 p-f5

Asahi Kogaku Kogyo K.K. 05.08.1994

Vario lens for a camera

The invention relates to a zoom lens for a camera, preferably for a compact camera.

As is well known, a zoom lens for a compact camera can have lower requirements in terms of rear focal length than a zoom lens for a single-lens reflex camera.

The following four types of zoom lenses are commonly used in compact cameras:

(I) A two-group system of a telephoto type consisting of a first lens group having a positive focal length and having an aperture position and a second lens group having a negative focal length. Such lens systems are disclosed in JP-A-56-128911, (the term "JP-A" used herein means "unexamined Japanese patent application"); JP-A-57-201213, JP-A-62-90611 and JP-A-62-264019 ;

(II) A three-group system which is a modification of the two-group system (I) and which consists of a first lens group having a positive focal length and aperture position, a second lens group having a positive focal length and a third lens group having a negative focal length and is disclosed in JP-A-58-184916;

(III) A four-group system consisting of a first lens group with a positive focal length, a second lens group with a negative focal length, a third lens group with a positive focal length and a fourth lens group with a negative focal length as disclosed in JP-A-60-57814; and

(IV) A three-group system which is a modification of the four-group system according to (III) in which the second and third lens groups are integrated into a common lens group, as disclosed in JP-A-62-78522.

The conventional zoom lenses described above have the following difficulties

Numerous versions of the two-group system (I) have been proposed. Although the system is a very simple (optically) .lens composition

used, this type of zoom lens suffers from the disadvantage that the first and second lens groups, especially the second lens group, must be moved a long distance during the zooming process, which presents difficulties in designing an effective mechanism.

The three-group system (II) differs from the two-group system (I) only in that the first lens group is divided into two collecting units, so that the path of the required lens movement is in no way smaller than in the first type.

The four-group system (III) shows a smaller amount of lens movement than the first two types.

Due to the complex structure resulting from the use of four lens groups and the strong refractive power provided by the individual lens groups, particularly the second and third lens groups, poor workmanship during the manufacture of the lenses can have significant adverse effects on the system properties, so that the greatest care must be taken during the manufacture of the lenses.

The three-group system (IV) requires a similarly small amount of lens movement as the four-group system (III), but it suffers from a greater degree of disturbance of the properties of the individual lens groups than types (I) and (II) if poor workmanship occurs during lens manufacture.

These systems (III) and (IV) have a common problem in that the lenses of the first group have a larger diameter than systems (I) and (II).

The zoom lens according to the present invention uses the method of zooming operation used in the conventional two-group system (I). The applicant of the present invention has previously proposed several versions of the system (I) which have a

smaller lens length despite increased rear focal length and which also with regard to reducing the

compared to other zoom lenses, two-group type in which the refractive power of the individual lens groups is increased, in particular by increasing the dispersive power of the second lens group to reduce the amount of movement. An example of this type of system is described in JP-A-62-264019 (hereinafter referred to as "previous invention"). However, this previous invention is in

disadvantageous in terms of cost/ as it requires no less than eight lens elements, which is too many for the purpose of achieving a zoom ratio of approximately two,

The present invention is based on the object of creating a zoom lens, preferably for a compact camera, which has a simple and compact design, is inexpensive to manufacture and enables good compensation of imaging errors.

According to the invention, this object is achieved with the features of claim 1.

Further developments of the invention emerge from the subclaims.

A zoom lens according to the invention can comprise, starting on the object side: a first lens group with a positive focal length and a second lens group with a negative focal length, wherein the zooming process is carried out by adjusting the distance between the two zoom lens groups. The first lens group with a positive focal length is composed, starting on the object side, of a first lens unit with a small refractive power, which has a positive or negative focal length, and a second lens unit with a positive focal length. The first lens unit has a

Two-group, two-element structure, which, starting on the object side, consists of a first collecting meniscus lens element which has a convex surface with a strong curvature directed towards the object, and a second meniscus lens element of great thickness which has a concave surface with a strong curvature on the object side and a convex surface with a strong curvature on the image plane side. The

first lens group meets the following conditions:

(!) l ^f iG ^/f i _a l ^< °· ³⁵

(2) 0.1 < d ₃ /f _s < 0.35

(3) 0.8 < h _xl /h _x4 < 1.0 where

£ _{ΔΓ is} the focal length of the first lens group; f is the focal length of the first lens unit; d_ is the thickness of the second meniscus lens element

f_, the focal length of the entire system in

wide angle range;

h , the height at which axis-parallel light rays

intersect the lens surface (first surface) of the first lens unit that is closest to the object; and

h . the height at which axis-parallel light rays intersect the lens surface (fourth surface) of the first lens unit closest to the image.

In a preferred embodiment, the first collecting meniscus lens element in the first lens unit satisfies the following condition:

(4) 0 < f /f. < 0.5

where f is the focal length of the lens element.

In another preferred embodiment,

the first collecting meniscus lens element has an aspherical surface.

In a further preferred embodiment, the first collecting meniscus lens element is a plastic lens with an aspherical surface and satisfies the following condition:

(4') 0 < fg/fjL < 0.3.

In a further preferred embodiment, the second lens unit is a bonded collecting lens with a divergent surface with high refractive power, which is constructed from a biconvex collecting lens element and a diverging meniscus lens element, which has a concave surface with high curvature on the object side.

In a further preferred embodiment, the second lens group, starting on the object side, is made up of a collecting lens element with a convex surface with a strong curvature directed towards the image plane and two collecting meniscus lens elements which have a concave surface with a strong curvature directed towards the object.

The invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1, 3, 4, 7 and 9 simplified cross-sectional views

of the zoom lens ⁱⁿ * wide angle range, which are constructed according to Examples 1 to 5 of the present invention;

Fig. 2(a), 4(a), 6Ca),

8(a), 10(a) graphical representation of

Aberration curves that correspond to the

Vario lenses of examples 1 to 5 in the wide-angle setting ;

Fig. 2(b),.4(b),

8(b), 10(b) Diagrams of the

Aberr.ation curves that match the

zoom lenses of Examples 1 to 5 at a medium focal length ; and

Fig. 2(C), 4(c), 6(c),

8(c) and 10(c) Diagrams of the

Aberration curves that correspond to the

Vario lenses of examples 1 to 5 in the telephoto range (narrow angle) can be achieved.

A first embodiment of the invention is described below.

The zoom lens according to the invention comprises, starting on the object side, a first lens group with a positive focal length and a second lens group with a negative focal length, whereby the zooming process is achieved by adjusting the distance between the two lens groups. The first lens group with a positive focal length is, starting on the object side, composed of a lens unit la with a small refractive power, which has a positive or negative focal length, and a further lens unit Ib with a positive

Focal length. The lens unit la has a two-group, two-element structure and consists/starting on the object side, of a first collecting meniscus lens element with a convex surface of large curvature directed towards the object and a second meniscus lens element of large thickness which has a concave surface with large curvature on the object side and a convex surface with large curvature on the image plane side. The first lens group satisfies the following conditions:

al < °· ³⁵

(2) 0.1 < d ₃ /f _g < 0.35

(3) 0.8 < _hxl / _hx4 < 1.0

in it is

f _1G is the focal length of the first lens group;

f, the focal length of the first lens unit (subgroup)

d., the thickness of the second meniscus lens element;

f _o the focal length of the entire system in the wide-angle range;

h , the height at which paraaxial light rays intersect the lens surface (first surface) of the first lens unit closest to the object; and

i.e. the height at which paraxial light rays intersect the lens surface (fourth surface) of the first lens unit closest to the image.

In a preferred embodiment, the first collecting meniscus lens element in the first lens unit satisfies the following condition:

(4) 0 < fg/^ < 0.5

where f is the focal length of the lens element.

The various conditions that must be met by a zoom lens system according to the present invention will now be described in more detail below.

Condition (1) concerns the refractive power of the first subgroup bz lens unit la in the first lens group. The lens unit la preferably has a small refractive power in order to reduce its sensitivity to poor processing during lens production. If the upper limit of condition (1) is exceeded, the refractive power of the lens unit la is increased and it becomes sensitive to poor processing during lens production, so that the production rate is reduced due to the large differences in the quality of the lenses produced.

Condition (2) concerns the thickness of the second meniscus lens element. If the upper limit of this condition is exceeded, the result is preferable in terms of effectively compensating aberrations, but on the other hand, the thickness of the lens element is increased to such an extent that its weight also increases noticeably, which is contrary to the important goal of reducing the lens weight. If the lower limit of condition (2) is not met, paraaxial light rays tend to pass through a lower portion of the fourth lens surface (this is related to condition (3) as described below) and the resulting decrease in the

·

I 5 * » 5 &Sgr; * *"* &diams;

Refractive power of the first lens unit la makes it difficult to reduce the overall length of the lens system.

Condition (3) also relates to the first lens unit la. As already stated in connection with condition (1), the lens unit la of the system according to the invention is characterized by a small refractive power. Despite this small refractive power, however, the lens unit la operates as if this unit were a wide-angle converter in a known afocal system. If the lower limit of condition (3) is not reached, the combined focal length of the first lens unit la and the second lens unit Ib is too small to achieve effective compensation of astigmatism at the maximum angle of view in the wide-angle setting. If the upper limit of condition (3) is exceeded, the lens unit la operates as a teleconverter instead of a wide-angle converter, thereby increasing not only the overall length of the lens system but also the amount of lens movement.

Condition (4) concerns the refractive power of the first converging meniscus lens element of the first lens unit la. As mentioned above, the lens unit la as a whole operates as a wide-angle converter with a small refractive power. If the upper limit of condition (4) is exceeded, the converging power of the first converging meniscus lens element becomes so large that the optical load on the divergent surface of the second meniscus lens system is increased to produce undesirable higher order aberrations. If the lower limit of condition (4) is not met, the first converging meniscus lens element is unable to have a positive focal length and the balance between the divergent surface of the second meniscus lens element is disturbed due to the difficulty in compensating for the field curvature.

t :

If the first converging meniscus lens element is provided with an aspherical surface, it is possible to achieve an even more effective compensation of astigmatism at the maximum angle of view in the wide-angle setting.

Condition (4*) determines the requirement that must be met in order to be able to manufacture the first converging meniscus lens element from a plastic material. This condition requires a smaller refractive power than condition (4). If the upper limit of this condition is exceeded, the focusing becomes highly sensitive to the temperature and humidity of the plastic material from which the first converging meniscus lens element is made. The resulting lens system is not suitable for use in a compact camera since it cannot be manually brought into a focused position, although it ensures good lens properties at normal temperatures. If the lower limit of condition (4 ¹ ) is not met, the same result is obtained as if the lower limit of condition (4) had not been met.

The lens construction of the system according to the invention is described in more detail below. One of the main features of this system is that the first lens unit la is composed of two meniscus lens elements. Despite the fact that the first lens group has a positive focal length, the first lens unit la can be equipped with the ability to work as a wide-angle converter by adopting a special construction of the geometry of the second meniscus lens element, whereas a conventional wide-angle converter has a diverging and a collecting lens element arranged starting on the object side.

The system according to the invention has no fundamental differences from the system of the previous invention with regard to the second lens unit Ib and the second lens group. In a preferred embodiment, however, the second lens unit Ib can be constructed as a cemented converging lens which has a divergent surface with a high refractive power and which is constructed from a biconvex converging lens element and a diverging meniscus lens element which has a concave surface with a large curvature on the

.*-»·.· object side. An advantage of this arrangement is that the collecting power of the first lens group is increased sufficiently to enable a reduction in the overall length of the lens system and that good properties can be ensured over the entire zoom range.

In another preferred embodiment, the second lens group can also be composed, starting on the object side, of a collecting lens element with a convex surface with a large curvature directed towards the image plane and two diverging meniscus lens elements with a convex surface with a large curvature directed towards the object.

..:||>·; directed concave surface of large curvature. This arrangement enables the refractive power of the second lens group to be increased by a substantial amount, thereby reducing the required amount of displacement of each lens group (particularly the second lens group) without affecting the lens properties.

Examples 1 to 5 of the present invention are described below with the aid of data sheets in which

F _N0 is the F-number,

f the focal length,

_w half the viewing angle,

B the rear focal length
r is the radius of curvature of each

lens surface,
d the lens thickness or the spatial distance

between the lens surfaces, N is the refractive index of a single lens at the

d-line, and

the Abbe number of a single lens

indicates.

The shape of an aspherical surface can be expressed by the following equation:

x = Cv ² A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸

_&Iacgr; 2 2

1-c y

This is

&khgr; the displacement of the vertex of a lens in the direction of the optical axis,

y is the displacement in a direction perpendicular to the optical axis;

C is a constant (the reciprocal of the radius

the curvature of the lens,at its vertex), and

A., A-, A ₀ asphericity coefficients.

4 &ogr;&ogr;

example 1

^FNO =

■γ = 30.6

Surface No.

3.6

5.1 23.4°-

7°

. r

21,482 28,350 -22,302 -32,334 37,359 -10,353 -17,940 -45,199 -17,234 -14,780 -49,158 -16,910 -54,155

Second surface: aspherical = 0.39440396X10" ⁴
= 0.87940830X10" ⁸

^f lG ^/f la ⁼ -

V ^f s

= 0.182

^{hxl /} hx4 = 0-948

1,879

2,100

6,552

3,695

4,178

1,300

11,550

3,010

2,203

1,350

2,289

1.400 f = 36.00 * f _B = 9.71 -

1.49186

(plastic

1.74000 1.58900

1.80518

6,471 - 3,467

1.80518 1.83400 1.83400

= -O.10963057xl0~ ⁶

50.00 23.45

. 57.4 lens )

28.3

48.6 25.4

25.4 37.2 37.2

68.00 41.13

V ^f l

= 0.218

Example 2

^F N0 =

3.6 ~ 5.1 * 6.9

= 30.6 ^σ ~ 23.4'- 17.

f = 36.00 ~ 50.00 " 68.00 f _B = 10.19 - 24.01 - 41.6

surfaces r 849 d N l/ No. 24. 005 1,678 1.58547 29.9 1 29. 443 1,952 (plastic lens ) 2 -23. 772 6,004 1.80518 25.4 3 -32. 310 4,094 4 38. 217 4,281 1.58875 51.2 5 -10. 178 1,581 1.80518 25.4 6 -17. 398 11,335 ' ' 6.659 - 3.46 7 -56. 807 3,034 1.80518 25.4 8th -17. 509 2,216 9 - -14. 942 1,350 1.83400 37.2 10 -70. 954 2,329 11 -17. 327 1,400 1.83400 37.2 12 -52. 13

Second surface: aspherical A. = 0.43505483X10" ⁴ A = -0.63119745XlO" ⁷

= 0.92651621xl0

~ ⁸

f /f,

= 0.167 = 0.939 = 0.140

Example 3

3.6

= 30.6°* 23.4

5.1 17.7°

Surface No.

1
2
3
4
5
6
7
8th
9

10
11
12
13

20,184 23,029 -21,745 -31,355 35,245 -10,236 -17,986 -41,660 -16,655 -14,658 -41,379 -16,246 -54,551

Second surface: aspherical

= 0.24426859x10

-4

= 0.58113040x10 ^f l _G / ^f la = -

-8th

= 0.174 = 0.954 = 0.203 1,760 2,291 6,246 3,565 4,192 1,535 11,690 3,055 2,059 1,350 2,253 1,400

f = 36.00 ~ 50.00 ~ 68.00 f _ß = 9.71 * 23.61 ~ 41.47

1.73101 1.76182

1.58900

1.80518

6,793 ~ 3,459

1.80518

1.83400 1.83400

^A 6 = -0.5974706IxIO" ⁷

s/

40.3 26.5

48.6 25.4

25.4 37.2 37.2

Example 4

= 1 : 3.6

5.1

6.9

f = 36.00 ~ 50.00 ~ 68.00

&iacgr;&Rgr; - 30.6~ ^f lG ^/f l 23.5 ^Y - 17 .8° 1. d _fB = 9.60 " 23.53 " Surface ^d 3/ ^f s 2. 996 No*. h _xl /h _x , 7. 343 V ^f l r 2. 600 N \S 1 18,226 4. 715 1.69350 53.2 2 24,406 1. 198 3 -19,917 11 318 1.83400 37.2 4 -30,583 3. .780 5 31,903 1. 469 1.58267 46.4 6 -9.876 1. 056 1.80518 25.4 7 -18,885 2. 350 " 6,839 ~ 3,476 8th -44,034 1. 596 1.80518 25.4 9 -14,871 400 10 -14,690 1.83400 37.2 11 -38,401 12 -14,293 1.83400 37.2 13 -56,299 _a = o.oii = 0.211 ₄ = 0.956 = 0.390

► «It

Example 5

^F N0 "

: 3.6

5.1

6.9

= 30.6° * 23.5 ^C " 17.8°

surfaces
No.

1
2
3

10
11
12
13

18,738

24,516

-19,778

-30,516

31,746

-9.865

-18,829

-39,803

-14.875

-14,417

-35,666

-14,576

-55,903

1,956 2,369 7,600 2,649 4,190 1,300 11,730 3,372 ,220 ,350 2,434 1,400

f = 36.00 ~ 50.00 ~ 68.00

f _B = 9.61 ~ 23.57 * 41.53

1.74950 1.80518

1.58267

1.80518

6,810 ~ 3,461

1.80518 1.83400 1.83400

35 .3 25 .4 46
25 .4
.4 25 .4 37 .2 37 .2

V ^f

= 0.012 = 0.211 = 0.958 = 0.389

As described above, the zoom lens according to the present invention is essentially the same as the system of the prior invention with respect to the second lens group, but is improved over the latter in terms of manufacturing cost by reducing the number of lens elements in the first group by one. Despite this reduction in the number of lens elements used, the zoom lens according to the present invention is as compact as the system of the prior invention and ensures comparable or better lens properties. In the zoom lens of the prior invention, the first lens group is composed of a first lens unit with a negative focal length, a second lens unit Ib with a positive focal length, and a converging lens element Im arranged between the lens units la and Ib. In contrast, the lens unit la in the system according to the present invention has a two-group, two-element structure which, starting on the object side, consists of a first converging meniscus lens element having a convex surface of high curvature directed towards the object and a second lens element of great thickness which has a concave surface of high curvature on the object side and a convex surface of high curvature on the image plane side and which is produced by integrating the crucial diverging lens element in the lens unit la and the converging lens element Im in the first lens group of the system of the prior invention into a continuous arrangement. In addition to the great simplicity of the structure of the lens unit la and its unique geometry, the lens group of the system according to the present invention is designed to satisfy the previously defined conditions (1) to (3) so that aberrations including spherical aberrations, spotting and astigmatism can be compensated in an effective manner.

Claims (8)

EXPECTATIONS 1. Vario lens for a camera, preferably for a compact camera, comprising, in the order seen from the object side, a positive first lens group and a negative second lens group, wherein the distance between the two lens groups is adjustable for focal length adjustment, (a) wherein the first lens group consists of the following subgroups: (al) a first subgroup of low refractive power with, in the order from the object side, - a positive first meniscus lens with a convex lens surface on the object side with strong curvature and a second meniscus lens of great thickness with a concave lens surface on the object side with strong curvature and a convex lens surface on the image side with strong curvature, and (a2) a positive second subgroup, and (b) wherein the first lens group satisfies the following conditions: (1) ^f l _G / ^f la| <°' ³⁵ ' (2) 0.1 < d_/f _e < 0.35 and (3) 0.8 < _hxl / _hx4 < 1.0, where: &iacgr;_&sfgr; Focal length of the zoom lens at Setting to shortest focal length,, F_ focal length of the first lens group, f- focal length of the first subgroup, xa d Thickness of the second meniscus lens, h ₁ penetration height of the paraxial light rays at the object-side lens surface of the first subgroup (penetration height at the first lens surface) and h . Penetration height of the paraxial light rays at the image-side lens surface of the first subgroup (penetration height at the fourth lens surface). 2. A zoom lens according to claim 1, wherein the first lens group satisfies the following further condition: (4) 0 < fjf. < 0.5, where f_ is the focal length of the first meniscus lens. 3. A zoom lens according to claim 2, wherein the first lens group satisfies the following condition: (4a) 0 < f _c /f _n < 0.4. - 22 - 4. A zoom lens according to claim 3, wherein the first lens group satisfies the following condition: (4b) 0 < fg/^ < 0.3. 5. A zoom lens according to any preceding claim, wherein the positive first meniscus lens of the first subgroup is aspherical. _^ 6. Vario lens according to one of the preceding claims, £·'■ wherein the positive first meniscus lens of the first Subgroup is made of plastic. 7. A zoom lens according to any preceding claim, wherein the second subgroup consists of a positive biconvex first lens and a negative lens cemented thereto, the concave cemented surface of the negative lens having a strong curvature. 8. A zoom lens according to any preceding claim, wherein the second lens group comprises, in order from the object side, a positive lens with a convex lens surface of strong curvature on the image side and two negative mensic lenses, each of which has a concave lens surface of strong curvature on the object side.