JPH03127011A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To compose the compact zoom lens for a lens shutter camera of a small number of lens elements by composing the front group of a positive, a negative, and a positive lens which are independent of one another and the rear group of one negative lens, and satisfying specific conditions. CONSTITUTION:The front group consists of the positive lens, negative lens, and positive lens which are independent of one another in order from the object side and the rear group consists of one negative lens; and the conditions shown by inequalities I and II are satisfied. In the inequalities I and II, psiW is the refracting power of the whole system at the wide-angle end, psiT the refracting power of the whole system at the telephoto end, psi1 the refracting power of the front group, psi2 the refracting power of the rear group, and beta the zoom ratio. Here, beta = psiW/ psiT and psi2 < 0. Consequently, while high optical performance is maintained, the compact zoom lens can be composed of a small number of lens elements.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and more particularly to a zoom lens for a lens camera with a built-in zoom lens.

In order to make a lens shutter camera with a built-in direct zoom lens more compact and lower in cost, there is a need to make the photographic lens more compact and lower in cost. In order to make the lens system more compact, including the amount of movement for zooming, it is necessary to increase the refractive power of each group, but increasing the refractive power while maintaining performance requires increasing the number of lenses. It can be said that the direction is to On the other hand, in order to reduce costs, it is effective to reduce the number of lenses.

In this way, there are many conflicting elements involved in making a lens system more compact and reducing its cost.

For example, a 2tc zoom lens with three lenses in the front group and one lens in the rear group, as proposed in Japanese Patent Application Laid-Open No. 60-48009, has not been made compact.

In addition, conventional zoom lenses with 38 to 90 iem specifications,
Since it costs $IIli for 7 to 8 lenses, cost reduction has not been achieved.

2 In view of this situation, an object of the present invention is to construct a compact zoom lens for a lens-shutter camera with a small number of lenses. For example, it is possible to achieve a zoom lens with a zoom ratio exceeding 2 using a total of four lenses, three in the front group and one in the rear group.

In order to achieve the above-mentioned purpose of "doing the task", the present invention sequentially performs the following steps from the object side:
In a zoom lens in which the focal length of the entire system is changed by changing the distance between the front group and the rear group, the front group has a front group having a positive refractive power and a rear group having a negative refractive power. In order from the object side, the lens is composed of a mutually independent positive lens, a negative lens, and a positive lens, and the rear group is composed of one negative lens and has a configuration that satisfies the following conditional expression.

0,07< ” ”<0.40 −・
−・−・１・−・■β・ψ.

here, ψー ψi ? I: Refractive power of the entire system at wide-angle end Refractive power of the entire system at the telephoto end Refractive power of front group 9) 2: Refractive power of rear group β: Zoom ratio However, β=ψ, 1/ψi h<0 It is.

These are conditions for keeping the overall lens length (distance from the front vertex of the lens to the film surface at the wide-angle end), the amount of movement for zooming, the back focus, and the state of correction of various aberrations in a good balance.

If the lower limit of conditional expression (■) is exceeded, it becomes difficult to maintain the back focus at an appropriate value (15% or more of the focal length at the wide-angle end) at the wide-angle end, leading to an increase in the diameter of the rear group lens.
Moreover, if the upper limit is exceeded, the amount of movement of the front group and the rear group due to zooming becomes excessive, which is disadvantageous in terms of the lens barrel configuration.

When the lower limit of conditional formula (■) is exceeded, the Petzval sum will take a large negative value, the image plane will tend to tilt in the positive direction, and in addition, the distortion at the wide-angle end will take a large positive value. become. Furthermore, if the upper limit is exceeded, it will be necessary to increase the distance between the front and rear groups during zooming, and the distance between the front and rear groups will be large at the wide-angle end.
This results in an increase in the total length of the lens.

It is preferable that the front group has at least one aspherical surface that satisfies the following conditional expression (2).In the conditional expression (0), the maximum effective diameter of the aspherical surface is y. II, 0.7y□ or <y<1. □For any height y in the vertical direction of the optical axis ysaw, -0,03<(N'-N
)・4゜(x (y) x0(y) /<0 −・・・−・
−・−・■Here, Gai: Refractive power of the front group N: Refractive index of the aspherical object side medium N゛: Refractive index of the aspherical image side medium x (y): Surface shape of the aspherical surface x0 ( y): Reference spherical shape of aspherical surface However, x (y) = r/ ε (1-(1-ε--≦do-Z, l/l) + ΣAi7' Ia! X 0(y) = 7 Xl ( 1-4)””>r:
Standard radius of curvature of aspherical surface ε: Quadratic surface parameter ^i: Aspherical coefficient? : Paraxial radius of curvature of aspheric surface (earth = upper 1,280)? It is r.

The above conditional expression (■) means that the positive refractive power becomes weaker (the negative refractive power becomes stronger) at the periphery of the aspherical surface in the front group,
This is a condition for correcting spherical aberration. When the upper limit is exceeded, spherical aberration tends to be undercorrected over the entire zoom range; when the lower limit is exceeded, the spherical aberration tends to be overcorrected over the entire zoom range.

In addition, the conditional expression (2) preferably includes at least one aspherical surface that satisfies the following conditional expression (2) in the rear group.
When ax, 0.8y□X<3'<1. For any optical axis vertical height y such as Oy*□, -0,10<9)・(N' −N)・,.

(x (y) −x0(y) )<o ・−・−・・
......■Here, 6: Refractive power of the rear group.

The above conditional expression (■) means that the negative refractive power of the aspherical surface in the rear group is weaker (the positive refractive power is stronger) at the periphery,
This is a condition for correcting distortion and field curvature in a well-balanced manner. When the upper limit is exceeded, the distortion aberration at the wide-angle end takes on a large positive value, and when the lower limit is exceeded, the image plane tends to be significantly curved in the negative direction over the entire zoom range.

It is desirable that all the aspheric surfaces in the front group satisfy the following conditional expression (2).

Conditional expression (■) is -0,02<6・(N' − N) ・ .

(x (y) −x0(y) )<o, ot
・−・−−・・−・・−■.

If the upper limit of conditional expression (2) is exceeded, the annular spherical aberration will have a large negative value, and a shift in the focus position due to aperture will become a problem. If the lower limit is exceeded, the effect of correcting the spherical aberration on the annular beam becomes excessive, making it difficult to correct various aberrations and spherical aberration in a well-balanced manner, and the spherical aberration tends to take on an undulating shape.

It is desirable that all the aspheric surfaces in the rear group satisfy the following conditional expression (2).

Conditional formula (2) is: -o, os<6・(N' − N) ・ .

(x (y) x0(y) )<0.02 ・
−・−・−・・■.

When the upper limit of conditional expression (2) is exceeded, the positive Oi shift tendency of positive distortion and field curvature increases in the intermediate field angle band from the wide-angle end to the intermediate focal length m region. Moreover, when the lower limit is exceeded, negative distortion becomes large from the intermediate focal length range to the telephoto end, and in addition, the negative shift tendency of the field curvature becomes significant in the entire zoom range.

Satisfying the following conditional expressions (1) and (2) is also effective for keeping the overall lens length, the amount of movement for zooming, the back focus, and the correction state of various aberrations in a good balance.

1.2<mu<2.4 −・−・−・−・−−−−−
−1・・・・−・−・■? W ψt 1.2 < 1-1 < 2.4 ・−・−・−・−・
■ψ− However, 9k<0.

Conditional expression (■) defines the ratio between the refractive power of the entire system and the refractive power of the front group at the wide-angle end.If the upper limit of conditional expression (■) is exceeded, the refractive power of the front group becomes excessive, and the refractive power of the front group increases. Even with an aspherical surface, it is difficult to correct various aberrations occurring in the front group, especially spherical aberration. Furthermore, when the lower limit is exceeded, there is a significant tendency for downward coma aberration to occur at the periphery of the screen.

Conditional expression (■) defines the ratio between the refractive power of the entire system and the refractive power of the rear group at the wide-angle end.If the upper limit of conditional expression (■) is exceeded, the rear group refractive power becomes excessive and the Even with an aspherical surface, it is difficult to correct various aberrations occurring in the rear group, especially field curvature and distortion. Furthermore, if the lower limit is exceeded, downward comatic aberration will occur significantly and it will be difficult to ensure sufficient back focus.

IL Team: Examples of compact zoom lenses according to the present invention will be shown below.

However, in each example, r and ~r represent the radius of curvature of the surface counted from the object side, d and ~d represent the distance between the axial surfaces counted from the object side, and N, ~N4+ Shi1 ~ Shi4 are It shows the refractive index and Atsube number of each lens for the d-line counted from the object side, and f is the focal length of the entire system, FM. indicates the open F number.

In addition, in the examples, a surface with a radius of curvature marked with * indicates that it is an aspherical surface, and the surface shape of the aspherical surface (
x (y) ).

<Example 1> Fso-3,6-5.3-7.9 Σd -40,311-34.013-29.811 defined by the formula representing f-thickness 39.3-58.5-86.6 Nirayotyosato five losses r1: εden 0.20803 x 10An -0,
17237x 10-'A&-0.63541X10
-' As vote 0.47391X10-" Al@ -0,20451X10-"Al1 Maro-
0.60700 = 0.19752X10-”ε=-0
, 22090 A, = 0.71791
0.53636
, 31809xlO-"<Example2> f = 39.3 to 58.5 to 86.6 FNO = 3.
6-5.4-8.1 Emperor's life Masaaki Enkei Blood plate member Okin'emu Eheni 37.740 d, 1.80O 1 1,51680 64,20 Σd = 40.532-35.903- 32.969 弗I劃ム(玖rl: ε=0.97223 A4--0.83452 x 10-'Aa"-0,
47778X10-' ra: g =0.96863A, =0.31
118xlO-'A,=0.25972xlO-'r,: ε=0.64974 A4=0.23514X10-'A4''0.17102X10-'r,l
ε=0.11397X10A4=0.24642Xl
O-'AM--0,69500xlO-'r9:A,=-0,24988x10-'^,.=-0,22930X10-" Alt = 0.36189xlO-"ε-0,99
085 A,=0.19054X10"'Ai=Q,21879x10-' As =-0,70301X10-" A,.=0.14671 X 10- "^,!
=0.19487X10-th <Example 3> f =39.3~58.5~86.6 FNO=3.6~5.4~8.2 Σd -40,526~36.133~33.468 4 matches of consecutive 14 “1: ε之0 na−−0,88580xtO−′ ＾h −−0,21947X10−′ As==−0,21425X10−′ A1゜=0.81040×10−” At* −0, 11824xlO-”ra:
g = 0.10000xlOA, 0.12252x
10-' A-Tength 0.72190 X 10-'As ”'
0.21386 X 10-”A, a--0,
28989X 10-”Lx = 0.2643
7X10-13r6: g =0.68081
^4-0.33088X10-' AM-0, 16942xlO-'As"-0,17850xlO-" Age =0.22719X10-"Lx =0.
35169XlO-"rl: a-0,10019XlOA4
Mo0.29143xlO-'AM--0,70790xlO-'As"-0,33869XIO-'A1゜=-0,21763X10-"Act=0.77879X10-13r9:
ε-0,93078 Aa=0.40781X10-'A&-0,32352x10-'A*=-0,87018xlO-' ^+o =0.17369X10-"Act =0
．． 18480X10-14 FIGS. 1 to 3 show the countries of construction of the lenses corresponding to Examples 1 to 3, and (A) in the figures shows the aperture.

Note that in FIGS. 1 to 3, arrows schematically indicate movement of the front group and the rear group from the widest angle 13ai (S) to the stationary far end (L). Furthermore, FIGS. 2 and 3 also show the movement of the front group related to floating.

Embodiment 1 includes, in order from the object side, a first lens consisting of a positive meniscus lens convex to the object side, a second lens consisting of a negative meniscus lens concave to the object side, a third biconvex positive lens, and an aperture (A ) and a rear group consisting of a biconcave negative fourth lens. Note that the object-side surface of the positive first lens, the image-side surface of the negative second lens, the image-side surface of the positive third lens, and the object-side surface of the negative fourth lens are aspherical surfaces. .

Example 2 shows, in order from the object side, a first lens that is more powerful than a positive meniscus lens that is convex to the image side, a negative second lens that is biconcave, a third lens that is positive that is biconvex, and a front group that is more dominant from aperture 0). The fourth lens is located at the bottom of the lens and the rear group. The fourth lens is a negative meniscus lens concave on the object side. Note that the object side surface of the positive first lens, the image side surface of the negative second lens, the image side surface of the positive third lens, and the negative fourth lens
The object-side surface and image-side surface of the lens are aspherical.

Furthermore, the reason why the air gap (d4) in the front group changes by a minute amount is due to floating.

Embodiment 3 is a front group consisting of, in order from the object side, a first lens that is more powerful than a positive meniscus lens that is convex to the image side, a biconcave negative second lens, a biconvex positive third lens, and an aperture (A). and the fourth
The rear group and the rear group are separated from each other by the lens. The fourth lens is a negative meniscus lens concave on the object side. In addition, the object side surface of the positive first lens, the image side surface of the negative second lens, the image side surface of the positive third lens, and the object side surface and image side surface of the negative fourth lens. is an aspheric surface.

Furthermore, the reason why the air gap (d4) in the front group changes by a minute amount is due to floating.

Figures 4 to 6 are aberration diagrams corresponding to Examples 1 to 3, in which (S) is the focal length at the wide-angle end M, (M) is the intermediate focal length, and (L) is the focal length at the telephoto end. It shows aberration. Furthermore, the solid line (d) represents the aberration for the d-line, the dotted line (SC) represents the sine condition, and the dotted line (DM) and solid line (DS) represent astigmatism on the meridional plane and sagittal plane, respectively. .

Tables 1 to 3 correspond to Examples 1 to 3, respectively.
(N' -N) 4 'd, Xx(y) -X・(y) ), 6・(N''-N
)・earth(x(y)

In addition, Table 4 shows -9 in conditional expression (■) in Examples 1 to 3.
'W'? y 9 ILEX-β・ψ in conditional expression ■,
β・niヱL11 17 in conditional expression ■ and 9' plate in conditional expression ■ 9'z 1-! ! -L-1 values are shown respectively.

? Table 1 (Example 1) Table 2 (H142) Table C11M3) Table As mentioned above, Examples 1 to 3 have a focal length of about 38 to
The main specifications are 90a+m. As mentioned above, conventional zoom lenses with this specification are composed of about 7 to 8 lenses, but according to the present invention, the number of lenses can be reduced to 4.
It becomes possible to make it into sheets.

As explained above, according to the present invention, it is possible to realize a compact zoom lens with a small number of lenses while maintaining high optical performance.

For example, a zoom lens with a zoom ratio exceeding 2 can be realized with a total of four lenses, three in the front group and one in the rear group.

Moreover, if the zoom lens according to the present invention is applied to a lens shutter camera with a built-in zoom lens, the camera can be made more compact and cost-effective.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 show countries in which lenses are constructed corresponding to Examples 1 to 3 of the present invention, respectively. FIG. 4, FIG. 5, and FIG. 6 are aberration diagrams corresponding to Examples 1 to 3, respectively. Temple No. 2!7'I Spherical aberration sine condition Astigmatism distortion white % Spherical aberration sine condition Astigmatism distortion amount % Spherical aberration sine condition Spherical aberration sine condition F8.2 Spherical aberration sine condition Astigmatism Astigmatism Accommodation distortion% 2 Yorei

Claims (3)

[Claims] (1) A zoom system that consists of a front group with positive refractive power and a rear group with negative refractive power in order from the object side, and changes the focal length of the entire system by changing the distance between the front group and the rear group. In the lens, the front group consists of a mutually independent positive lens, a negative lens, and a positive lens in order from the object side, and the rear group consists of one negative lens and satisfies the following conditional expression. Zoom lens: 0.07<√(ψ_W・ψ_T)/β・ψ_1<0.4
00.07<|√(ψ_W・ψ_T)/β・ψ_2|<
0.50 where, ψ_W: refractive power of the entire system at the wide-angle end ψ_T: refractive power of the entire system at the telephoto end ψ_1: refractive power of the front group ψ_2: refractive power of the rear group β: zoom ratio, however, β=ψ_W/ ψ_T ψ_2<0. (2) The zoom lens according to claim 1, characterized in that the front group has at least one aspherical surface that satisfies the following conditional expression: The maximum effective diameter of the aspherical surface is y_m_a_x. When, 0.
7y_m_a_x<y<1.0y_m_a_x
)−x_0(y)}<0 where, ψ_1: Refractive power of the front group N: Refractive index of the aspherical object-side medium N': Refractive index of the aspherical image-side medium x(y): Refractive index of the aspherical surface Surface shape x_0(y): Reference spherical shape of aspheric surface However, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ r: Reference radius of curvature ε of aspheric surface: Quadratic surface parameter Ai : Aspheric coefficient ■: Paraxial radius of curvature of aspheric surface (1/■=1/r+2A_2). (3) The zoom lens according to claim 1, characterized in that the rear group has at least one aspherical surface that satisfies the following conditional expression: The maximum effective diameter of the aspherical surface is y_m_a_x. When, 0.
For any vertical height y of the optical axis such that 8y_m_a_x<y<1.0y_m_a_x, −0.10<ψ_2・(N′−N)・d/dy{x(y
)−x_0(y)}<0 where, ψ_2: Refractive power of the rear group N: Refractive index of the aspherical object-side medium N': Refractive index of the aspherical image-side medium x(y): Refractive index of the aspherical surface Surface shape x_0(y): Reference spherical shape of aspheric surface However, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ r: Reference radius of curvature ε of aspheric surface: Quadratic surface parameter Ai : Aspheric coefficient ■: Paraxial radius of curvature of aspheric surface (1/■=1/r+2A_2).